ORANGE BOOK Flashcards
‘Z’ is the number of protons in the nucleus
True: Z is the atomic number and indicates the number of protons in the nucleus.
‘A’ determines an element’s place in the periodic table.
False: A is the mass number. Z determines place in the periodic table.
A stable nucleus contains equal numbers of protons and neutrons.
False: Higher atomic number nuclei require more neutrons than protons for stability.
Binding energy is that required to excite an electron to a higher energy shell.
False: Binding energy is expended completely removing the electron from the atom.
Protons are loosely bound to neutrons in the nucleus.
False: They are tightly bound.
Electrons are arranged in shells around the nucleus at specific energy levels.
True
A proton has a mass approximately 1850 times that of an electron.
True
Characteristic radiation is produced from the valence shell.
False: Characteristic radiation is from inner shells.
The valence shell gives the chemical properties.
The binding energy is highest for a valence shell electron.
False: It is lowest for valence shell electrons and highest for the K shell.
K shell binding energy increases with increasing atomic number.
True
In a vacuum, velocity of radio waves is equal to that of infrared light.
D. True All electromagnetic radiation travels at the speed of light in a vacuum.
There can be up to 8 electrons orbiting the nucleus in the L shell.
True:There can be up to 2 electrons in the K shell, 8 in the L shell, 18 in the M shell and 32 in the N shell.
Nuclides have the same chemical properties between isotopes of a particular element.
True: Isotopes have the same number of protons and therefore when neutral the same number of electrons.
An electron is not a nucleon.
True: Neutrons and protons are nucleons.
Nuclides are isotopes if they have the same atomic mass but different atomic number.
False: Nuclides with the same number of protons but different number of neutrons are isotopes, therefore they have the same atomic number and different atomic mass.
Velocity of electromagnetic radiation increases as energy increases.
False: Frequency increases with energy, but velocity is constant.
Frequency and wavelength of electromagnetic radiation are directly proportional to each other
FALSE. They are inversely proportional.
Visible light has a shorter wavelength than ultraviolet light.
FALSE. UV light has a shorter wavelength than visible light and is part of the electromagnetic spectrum
EM radiation includes beta radiation
False: Beta particles are electrons emitted from the nucleus.
EM radiation travels in straight lines if unattenuated.
True
Ionising radiation:
Causes direct damage if it is absorbed in tissue
True
EM radiation has energy that is usually expressed in Joules in diagnostic radiography
False: Electron volts (eV), which give manageable numbers for calculations (1eV = 1.6 x 10-19Joules).
Ionising radiation:
Causes indirect damage through ionization of water and production of free radicals
True
Ionising radiation:
Always obeys the inverse square law.
False: Only applicable to types of electromagnetic radiation from a point source and without attenuation.
Ionising radiation: Is useful in medical imaging in all its forms.
False: Gamma and x-rays are useful, neutrons, alpha, and beta particles are not.
Ionising radiation: May require only to be shielded with Perspex.
True: Beta radiation may require only Perspex shielding, however optimal shielding is achieved with Perspex backed with lead.
Secondary electrons: They are recoil electrons produced during Compton scattering events.
True
Secondary electrons: range depends only upon the density of the material through which they are travelling.
True
Secondary electrons can interact with inner shell electrons of atoms they pass causing ionization.
False: They interact with outer shell electrons to cause ionization.
Secondary electrons are the reason that x-ray and gamma rays are indirectly ionizing.
True: Alpha and beta particles are directly ionizing as they are charged.
Secondary electrons cause heat
Energy from the x-ray beam is converted into increased molecular motion and therefore heat.
β minus decay reduces atomic number by 1
False. Neutron -> Proton increases Z / atomic number by 1
Alpha particles are helium nuclei.
True
Some radionuclides emit electrons and characteristic x-rays
True: During internal conversion a K shell electron is ejected, producing characteristic x-rays when the K shell vacancy is filled with an electron from the L shell.
Radioactive decay is the number of disintegrations per minute.
False: Disintegrations per second (Bequerels (Bq)).
Most nuclides left in a metastable state after beta decay, emit gamma rays to reach ground state.
True:This is isomeric transition.
Positron emission reduces the number of protons in an atom by 1.
True.
Decay rate can be increased by increasing temperature.
False: Decay rate is not affected by physical conditions.
If stored long enough, the radioactivity of a radionuclide will drop to zero.
False. Radioactivity never reaches zero because of exponential decay.
Gamma emitting radionuclides with shorter half life are safer to use and store than those with longer life
True: Shorter time to decay to negligible activity is safer.
Beta emission is at a continuous range of energies.
True: Beta emission is at a continuous range of energies up to a maximum (Emax) and with average energy approximately Emax / 3.
Radioactive decay constant is the probability of nuclear decay per unit time.
True: Decay constant is the fraction of nuclei decaying per unit time.This is the
probability of decay, as decay of individual atoms occurs at random and cannot be predicted.
Physical half-life (t1/2) is the time taken for the activity to decay to ½ the original value.
True
Gamma rays are emitted at a single photon energy.
False: More than 1 photon energy may be emitted.
In 10 half-lives the activity is reduced by a factor of approximately 1000.
True - factor of 1024
Only one type of radiation is emitted by a radionuclide.
False: Often there is beta and gamma, or alpha and gamma emission together.
Direct emission from radioactive decay includes:
A. Beta minus emission.
B. Characteristic x-rays.
C. Bremsstrahlung.
D. Alpha particles.
E. Positron emission.
A.True: Occurs in radionuclides with neutron excess.
B. True: Through internal conversion or K-shell capture.
C. False: This is due to interactions of electrons with the electric field around the nucleus and not of decay directly.
D. True.
E. True: Occurs in radionuclides with neutron deficit.
Beam intensity is the total energy per unit area per unit time.
True
The inverse square law applies to all x-ray beams
False: This only applies to x-rays from a point source.
X-rays have lower linear energy transfer than alpha particles.
True: Alpha particles are heavy and produce ionizing events closely spaced along a short path, causing maximum DNA damage.
All electromagnetic radiation can cause ionization
False: Only high-energy photons (x-rays/gamma rays) are ionizing.
At equivalent energy, an x-ray cannot be distinguished from a gamma ray.
True: How they are produced differs, but they are indistinguishable at equivalent energies.
X-rays
Produced when electrons are accelerated or decelerated, or when they rearrange within an atom. X-rays can be produced naturally or by machines.
Gamma rays
Produced when an excited nucleus of a radioactive element undergoes radioactive decay. Gamma rays can also be produced by particle annihilation.
Usually a voltage of 10V and a current of 10A pass through the filament.
True: This heats the filament to incandescence, so that electrons can be boiled off by thermionic emission in order to be accelerated across the tube.
The accelerating voltage of the tube is typically in the range 60-120kV.
The process of thermionic emission occurs on the surface of the anode.
False: It occurs at the surface of the cathode.
When an accelerating electron interacts closely with a target nucleus it is deflected and slowed, losing energy that is emitted as an x-ray photon.
True: This is Bremsstrahlung, or braking radiation, which results in the continuous spectrum of radiation.
The angle of the target ensures that all x-rays produced pass through the window in the tube to form a beam.
False: X-rays will be produced in many directions, but only those that pass through the window will contribute to the useful beam, the others will be absorbed by the tube housing.
X-ray production in a diagnostic x-ray tube:
Is more efficient with a rotating compared to a stationary anode.
True
X-ray production in a diagnostic x-ray tube:
Requires a cooling air current at all times within the tube.
False: The tube contains a vacuum.
Radiation output from an x-ray tube increases with:
A constant potential compared to a single phase waveform.
True
Heat is only removed to the tube envelope by conduction.
False: Heat is radiated through the vacuum to the envelope.
X-ray Rotor bearings are lubricated with oil.
False: Silver is used oil would evaporate in the vacuum.
The anode stem is a poor heat conductor.
True: Prevents damage to the rotor assembly.
The addition of rhenium to the tungsten target increases toughness and lifespan of the target.
True: This alloy reduces surface pitting and increases lifespan.
X-ray anode angle is generally 20-35°.
False: The angle is generally 7-20°.
X-ray tube the anode angle increases the tube rating if the angle is reduced.
True
An x-ray tube rating is the maximum amount of kilowatts (kW) that can be safely used in a 0.1 second period
Diagnostic x-ray tube the anode angle
determines the size of field covered by the x-ray beam at a given focus-film distance.
True
Spectrum of an x-ray beam is not affected by filtration.
False: Increasing mA merely increases the number of photons.
Their energy and therefore the shape of the spectrum remains the same if kV is unaltered.
Double check - does it not increase the area under the curve
x-ray beam spectrum MAX/PEAK (as in photon number) is 3/4 kVp
FALSE. 1/3-1/2 Max kVp
Tungsten is used as a filament because of its high atomic number.
False:This is the reason that it is chosen for the anode.
Tungsten used because of high melting point and high resistance.
x-ray tube filament should have a low vapour pressure
True: A good property for thermionic emission
Anode heel effect results in more attenuation on which side
Photons on the ANODE side of the beam have more target material to travel through, so are attenuated and the intensity reduced.
Anode-heel effect is not advantageous in radiography
False: Mammography
Anode-heel effect is greater if target angle is steeper
True: The steeper the target, the further through the target material the photons on the anode side of the beam have to travel and the more attenuated they are.
Steeper = SMALLER angle
Anode-heel effect more noticeable if the focus-film distance is increased
False: With increased distance the beam diverges further and the film only intercepts the central part of the beam.
22 Increasing tube kV (with all other factors constant) increases:
Patient entrance surface dose.
True
22 Increasing tube kV (with all other factors constant) increases:
Scattered compared to primary radiation at the film.
True: Higher kV x-rays are more penetrating so scattering events occur deeper in the patient nearer the film.Also, the scattered photons are more penetrating.
22 Increasing tube kV (with all other factors constant) increases:
Radiographic contrast.
False: Contrast decreases as kV increases.
22 Increasing tube kV (with all other factors constant) increases:
Film blackening.
True: Increased kV causes increased exposure and increased film density.
22 Increasing tube kV (with all other factors constant) increases:
Photoelectric interactions compared to Compton interactions.
False:At higher kVs Compton events predominate
Increased tube filtration increases the half value layer.
True: Through beam hardening. Average beam energy is higher
Total attenuation is the product of Compton, photoelectric, and elastic attenuation effects.
True: This is the total attenuation. Attenuation coefficient is the sum of each process.
Half value thickness is inversely proportional to the linear attenuation coefficient.
True: Half value layer is 0.69/µ (µ = linear attenuation coefficient = fraction of the primary beam that is removed per unit distance).
Attenuation is altered by atomic number
True: Attenuation is increased with increasing Z number and increasing density of the attenuating material, through increased Compton scatter and photoelectric absorption. (The probability of photoelectric absorption is proportional to X
Attenuation is related inverse square law
False: Attenuation is the reduction in intensity due to interactions in matter, whereas the inverse square law is the reduction in intensity due to beam divergence from a point source.
HVL is thickness of a material that will reduce the intensity of a narrow x-ray beam to 50%
True. Exponential as 50% for every HVL.
HVL is a measure of the penetrating power of an x-ray beam.
True
HVL is for lead is greater than for aluminium at a given energy of x-ray beam.
False. Lead has a higher Z, no HVL needed is smaller
HVL is reduced as the photon energy of the radiation decreases.
True
Mass attenuation coefficient: Is measured in cm2/g.
True
Mass attenuation coefficient: Linear attenuation coefficient / density
True
Mass attenuation coefficient is less for water than for ice
False: It is equal for water and ice, as it is independent of physical density.
Mass attenuation has many practical applications in diagnostic radiology.
False: The linear attenuation coefficient has more practical applications, as film density produced by a certain depth of tissue is more useful than that produced by a certain mass of tissue.
Mass attenuation coefficient is proportional to the linear attenuation coefficient.
True. Mass attenuation coefficient is the linear attenuation coefficient / density
Linear attenuation coefficient: fractional reduction in intensity per unit thickness.
True. fractional reduction in intensity per unit thickness.
Linear attenuation coefficient: can be used to calculate the half value thickness.
True: HVL = 0.693 / linear attenuation coefficient.
So HVL is INVERSELY PROPORTIONAL to LAC
Linear attenuation coefficient: increases as photon energy increases.
False: It decreases as photon energy increases.
Less fractional reduction in intensity per unit thickness due to higher energy and more penetrance
Linear attenuation coefficient: It is measured in mm.
False. Its PER mm or mm^-1
The greater the difference in linear attenuation coefficients between two tissues, the greater the contrast between them.
True: Contrast is proportional to the product of the difference between the 2 linear attenuation coefficients and the thickness of the tissues involved.
Regarding scattered radiation: More is measured on the tube side of the patient in diagnostic radiology.
True: Most interactions occur at the entrance surface of the patient and forward scattered photons are more attenuated than backscattered ones.
Regarding scattered radiation: A Compton scattered photon is deflected from its path with no loss of energy.
False: This is elastic scattering.
Regarding scattered radiation: There is no ionization with elastic scattering.
True
Regarding scattered radiation: During a Compton interaction a photoelectron is produced.
False: These are formed in photoelectric interactions.
Regarding scattered radiation: At higher kV more photons are deflected through large angles.
C. True.
In Compton scattering: There is an interaction with a free electron.
True: The incident photon interacts with an outer shell an electron.
In Compton scattering: The recoil electron can be scattered in any direction.
False: The scattered photon can be emitted in any direction, but the recoil electron can be projected only forwards or sideways.
In Compton scattering: The larger the angle of scatter, the greater the reduction in energy of the incident photon.
True
In Compton scattering: All the photon’s energy can be transferred to the electron.
FALSE. The photon is scattered and therefore still retains some energy.Total absorption occurs in photoelectric interactions.
In Compton scattering: The amount of scatter is proportional to electron density.
True: The greater the concentration of electrons, the greater the probability of an interaction.
Concerning the photoelectric effect: incident photon completely disappears
True. NO SCATTERED RADIATION
Compton Scatter predominates in bone above
50kV
Compton Scatter predominates in tissue above
30kV
Concerning the photoelectric effect: main attenuation process in bone at 80kV.
False: The photoelectric effect predominates over Compton scatter in bone BELOW 50kV
The probability of a photoelectric interaction increases as photon energy increases.
FALSE. The probability of photoelectric interaction is inversely proportional to photon energy cubed.
The photoelectric effect: Involves free electrons.
False: It involves inner shell electrons. And produces characteristic radiation. Not just K shells but L.
The photoelectric effect: Is most important at the lower end of the diagnostic range of energies.
True: As an electron is removed a net negative charge results.
The K-absorption edge is important when choosing an x-ray filter, a contrast medium or an imaging phosphor.
True
An x-ray filter does not transmit photons well if they are of an energy equivalent to its own K-absorption edge.
False: It will be relatively transparent to photons of the energy of its absorption edge.
Barium has such a high atomic number that its K-absorption edge does not play a role in diagnostic imaging when it is used as a contrast medium.
False: The atomic number of barium is 56 and the K-absorption edge is 37keV. Diagnostic x-ray beams contain a high proportion of photons around this energy, ensuring a high probability of photoelectric interactions.
Filtration of an x-ray beam: Reduces the maximum photon energy (kVp).
False:The kVp remains the same, but lower energy photons are filtered out and average kV increases.
Filtration of an x-ray beam: By the patient is known as inherent filtration.
False: Inherent filtration results from absorption of x-rays as they pass through the X-RAY TUBE.
Filtration of an x-ray beam: Improves the rating of the x-ray tube
True.
Filtration of an x-ray beam: Is more effective for filtering high energy x-rays using a copper rather than an aluminium filter.
True: Copper has a higher atomic number than aluminium, so is better at filtering higher energy x-rays.
Filtration of an x-ray beam: Results in an image with improved contrast.
False: Filtration hardens the beam by increasing the mean energy of the photons, therefore contrast in the image is decreased.
Inherent filtration of an x-ray tube: Absorbs high energy x-rays.
False:Absorbs low energy x-rays.
Inherent filtration of an x-ray tube: Causes beam hardening.
True: By removing low energy photons and increasing the average energy of the beam.
Inherent filtration of an x-ray tube: Is increased if beryllium instead of glass is used in the tube window.
False: Beryllium has a lower atomic number than glass, therefore filtration is less.
Inherent filtration of an x-ray tube: Is usually equivalent to 2.5mm aluminium.
False: Total filtration is approximately 2.5mm Al, inherent is 0.5 - 1mm.
Inherent filtration of an x-ray tube: Is mostly due to the oil.
False: Due to target, tube window, and the oil.
Added filtration: Does not affect patient entrance dose.
False: Absorbs low energy x-rays.
Added filtration: Alters the quality of the x-ray beam.
True. By removing low energy photons and increasing the average energy of the beam.
Added filtration: May consist of a compound filter.
True: Copper is used with a backing of aluminium on the patient side to absorb the 9kV characteristic radiation from the copper.
Added filtration: Is generally made of aluminium in diagnostic tubes.
True.
Added filtration: Does not affect the intensity of the beam.
False: Intensity or amount of radiation is decreased by the filter.
X-ray tube rating increases with: Rotating compared to stationary anodes.
True: There is more efficient heat loss from a rotating anode, so the rating is higher.
X-ray tube rating increases with: Larger focal spot size.
True: A larger focal spot causes less heating than if the beam were focused onto a smaller area.
X-ray tube rating increases with: Increasing the anode angle with fixed focal spot size.
False: A smaller anode angle has a higher heat rating.
X-ray tube rating increases with: Half wave compared to full wave rectification.
False: Rating is increased with full wave rectification.
X-ray tube rating increases with: Quicker production of heat.
E. False: This makes the tube rating lower.
Measurement of radiation dose: Can be read directly through an electronic read-out from photoconductive silicon diodes.
True: Useful for personal dosimeters and quality assurance
Measurement of radiation dose: Is useful for personal and patient dosimetry with the use of thermoluminescent dosimeters.
True
Measurement of radiation dose: With a dose area product meter provides a figure with the units cGy cm3.
False: It is the product of dose and area with units cGy cm2.
SQUARED NOT CUBED
Measurement of radiation dose: May be carried out using thimble ionization chambers within the field of interest.
True
Measurement of radiation dose: For staff may utilize the photographic effect of silver bromide in a film badge.
True
Film badges: Use double emulsion film.
True: If the fast emulsion is over-exposed by a high-dose exposure, the slow emulsion can be read.
The following are true of thermoluminescent dosimeters:
The phosphor used is commonly lithium chloride.
False: Lithium FLUORIDE.
Film badges: Use cadmium nuclei to detect neutron exposure.
True: The interaction of neutrons with the cadmium nuclei results in gamma ray emission that is detected by the film.
Film badges: Are calibrated with a caesium source.
True.
Film badges: Have an open window for the detection of beta particles.
True.
Film badges: Should be analysed once a year when monitoring staff.
False: They are subject to environmental effects, so should not be used for longer than a month.
The following are true of thermoluminescent dosimeters:
X-ray interactions involve outer shell electrons of the thermoluminescent phosphor.
True: Valence shell electrons are involved.
The following are true of thermoluminescent dosimeters:
When exposed to radiation, interactions excite electrons that become trapped in the forbidden energy band.
True: A valence shell electron is excited into the conduction band and then falls back into an electron trap in the forbidden energy band.
The following are true of thermoluminescent dosimeters:
The amount of light produced depends on the energy of the photons involved in the exposure.
True.
Regarding luminescence:
It is the process by which a material absorbs energy from an external source and re emits it as light.
True.
The following are true of thermoluminescent dosimeters:
Their response is linear with dose over a wide range.
True.
Regarding luminescence:
Fluorescence is the delayed emission of light following energy input.
False: Fluorescence is the instantaneous emission of light following energy input.
PHOSPHORESCENCE is the delayed emission of light.
Regarding luminescence:
For light to be emitted from a phosphor, electrons in the electron traps must fall to the conduction band.
FALSE.
False: The x-ray photons excite electrons from the valence band to the conduction band, where they then fall into electron traps.
They must fall BACK TO VALENCE BAND for light to be emitted.
Regarding luminescence:
After irradiation, a thermoluminescent phosphor must be stimulated with a laser for light to be emitted.
False: THERMOluminescence requires HEATING.
PHOTOstimulable luminescence requires light.
Regarding luminescence:
Intensity of light emitted from a phosphor is proportional to the intensity of the irradiating x-ray beam.
True.
Deterministic effects of ionizing radiation include:
A Cataract
B. Epilation
C. Leukaemia
D. Lung cancer
E. Erythema
The deterministic effects are: Cataract, Epilation, Erythema
Deterministic: Damage depends on absorbed dose, Threshold exists
Stochastic effects of radiation include:
A Infertility
B. Leukaemia
C. Cataract
D. Cancer
E. Hair loss
The Stochastic effects are: Leukaemia and cancer
Stochastic:
Severity is independent of absorbed dose
Threshold does not exist
Probability of occurrence depends on absorbed dose
Equivalent dose: Is derived from absorbed dose multiplied by a tissue weighting factor.
FALSE. Equivalent dose = Absorbed dose x radiation weighting factor
ED = AD x RWF
Equivalent dose: Is measured in Sieverts (Sv).
True
Equivalent dose:
Is averaged over all tissues of the body.
False. Equivalent dose = absorbed Dose multiplied the appropriate radiation weighting factor.
Equivalent dose is calculated for individual organs.
Equivalent dose is expressed in millisieverts (mSv) to an organ.
Effective dose is calculated for the whole body.
It is the addition of equivalent doses to all organs, each adjusted to account for the sensitivity of the organ to radiation.
Effective dose is expressed in millisieverts (mSv).
Equivalent dose: Is the same as absorbed dose for neutrons.
False. As the radiation weighting factor for neutrons range from 5 to 20.
Equivalent dose: Is the same as absorbed dose for neutrons.
False. Equivalent dose = absorbed Dose multiplied the appropriate radiation weighting factor.
Equivalent dose: Takes into account sensitivity of the tissues to radiation.
False. It is based on the absorbed dose to an organ, adjusted to account for the effectiveness of the type of radiation (radiation weighting factor).
The radiation weighting factors are needed because different types of radiation (like alpha, beta, gamma, and neutrons) can have different effects even if the absorbed dose is the same.
Absorbed dose:
Absorbed dose is the amount of energy deposited by radiation in a mass.
The mass can be anything: water, rock, air, people, etc.
Absorbed dose is expressed in milligrays (mGy).
Absorbed dose: Relative to an organ depends on its mass.
Depends on the radiation weighting factor.
Is the amount of energy deposited per unit mass to a medium.
False.
Absorbed dose is the amount of energy deposited by radiation in a mass.
Absorbed dose: Is measured in Joules/Kg.
True. The unit is Gray & 1 Gray= 1 Joule/Kg.
Absorbed dose: Is measured in Sieverts.
False. Equivalent and effective doses are measured in Sieverts (Svt)
Absorbed dose = Gy or Joules/Kg
Absorbed dose: depends on radiation weighting factor
False. Energy deposited per unit mass
Equivalent dose for radiation weighting factor.
DOSE EQUIVALENT FOR EACH TYPE OF RADIATION.
Absorbed dose: Is the amount of energy deposited per unit mass to a medium.
True.
Effective dose: Is derived from absorbed dose multiplied by a tissue weighting factor.
False. EQUIVALENT Dose x tissue weighting factor
Effective dose: Is measured in Gray.
False. Measured in Sv
Effective dose: Takes into consideration the different radiosensitivity of tissues.
True
Effective dose: Combines organ doses to give a whole body dose.
True
In a dental film is in the order of 0.004mSv.
True
Regarding ionizing radiation:
A Neutrons are low LET (linear energy transfer) radiation.
False. Neutrons are high-LET radiation.
The radiation weighting factor for alpha particles is 20.
True. The radiation weighting factor for alpha particles is 20.
X-rays and beta particles have the same radiation weighting factor.
TRUE. The radiation weighting factor for both is unity.
The radiation weighting factor for neutrons is unity.
False. Neutrons is is 5-20 depending on the radiation energy.
For x-rays absorbed dose is equal to the equivalent dose.
True. RF for XRs, Gamma and beta particles is 1.
The following tissues have a high carcinogenic risk from radiation (more than or equal to 0.12 tissue-specific weighting factor):
Colon
Skin
Breast
Bone marrow
Oesophagus
Colon T
Skin F
Breast T
Bone marrow T
Oesophagus F
Lung Breast Stomach 0.12
Colon 0.12
Red bone marrow 0.12
Gonads LOWERED from 0.2 to 0.08
The following tissues have a moderate carcinogenic risk from radiation (0.05 in tissue-specific weighting factor):
Skin
Gonads
Lung
Breast
Bone
Skin F
Gonads F
Lung F
Breast F
Bone F
BLOT
Bladder 0.05
Liver 0.05
Oesophagus 0.05
Thyroid 0.05
tissues with the LOWEST carcinogenic risk WT 0.1
Tissue weighting factor of 0.1:
Bone surface, skin,
brain, salivary glands
Unit for entrance surface dose is
Gy
Unit for equivalent dose
Sv
Dose area product (DAP) units
Dose area product (DAP)-Gy cm2
AREA = CENTREMETRES SQUARED
Absorbed dose units
Joules/kg or Gy
Effective dose units
Sv
Regarding deterministic effects:
Diarrhoea and vomiting are examples.
There is a threshold dose above which they do not occur.
Effects occur by chance.
The threshold dose is the same for different deterministic effects.
Severity increases with increasing dose.
Regarding deterministic effects:
True. Diarrhoea and vomiting are example
False. Threshold BELOW that deterministic effects do not occur.
False. Occur dose dependantly
False. Different thresholds
True. Severity increases with increasing dose.
Regarding stochastic effects:
The probability of a stochastic effect is independent of dose.
Occur immediately after exposure to ionising radiation.
Have a linear no threshold theory.
Sterility is an example.
Breast cancer is an example.
Regarding stochastic effects:
False. Probability increases with increasing dose.
False. They occur after a latent period which lasts for many years.
True. Have a linear no threshold theory. They occur by chance and are not dose dependent but the chance of developing stochastic effects increases with the dose.
Sterility is NOT example.
Breast cancer IS an example.
In the daily practice of diagnostic radiology stochastic effects are commoner than deterministic effects.
FALSE. Deterministic effects are more common (think therapeautics)
The chances of producing deterministic effects is the same for x-rays and gamma rays.
True. Both RF =1
No dose is considered safe for deterministic effects.
False. Thresholds exist for deterministic effects.
No dose safe for stochastic effects.
Deterministic effects may be non-additive.
True. Deterministic effects may be non-additive.
Beta particles travel through matter at high speeds.
True
Alpha particles travel through matter at low speeds.
Alpha particles have a large mass and double charge making them travel slowly through matter.
Alpha particles are similar to the nucleus of hydrogen.
False: They are similar to helium nucleus with 2 protons and 2 neutrons.
Beta particles are heavier than alpha particles.
False: Alpha particles are heavier.
Alpha particles have useful applications in diagnostic radiology.
False:They produce a large amount of ionization per unit length of the medium through which they travel making them unsafe for use in radiology.
Entrance surface dose are typical for PA chest film - 0.15 mGy.
True. Entrance surface dose are typical for PA chest film - 0.15mGy.
Entrance surface dose are typical for Lateral lumbar spine x-ray - 12 mGy.
True. Entrance surface dose are typical for Lateral lumbar spine x-ray - 12mGy.
Entrance surface dose are typical for AP skull x-ray - 2mGy.
True: DRL is 3mGy.
Entrance surface doses are typical for AP abdomen film - 8 mGy.
False: Entrance surface dose is usually 5mGy. The DRL for an abdominal film is 7 mGy.
Fluoroscopy ENTRANCE surface dose rate - 100 - 150 mGy/min.
False: The skin or entrance surface dose rate of fluoroscopy is 5-50 mGy/min.
Abdominal Imaging:
Approximate Effective Doses for
Intravenous Urography (IVU)
CT Colonoscopy
Computed Tomography (CT)–Abdomen and Pelvis
Computed Tomography (CT)–Colonography
Barium Enema (Lower GI X-ray)
Upper GI Study with Barium
Computed Tomography (CT)–Abdomen and Pelvis, repeated with and without contrast material
https://www.radiologyinfo.org/en/info/safety-xray
Intravenous Urography (IVU) 3mSV
CT Colonoscopy = 6mSV
All double = 8mSV
Dual Phase = 15mSV
Head imaging:
Approximate Effective Doses for
CT H&N
CT Brain repeated with and without contrast
CT Chest
CT CA
CT Spine
CT H&N 1.2 mSv
CT Brain 3.2 mSv
CT Chest 5
CT CA 9
CT Spine 9
The effective dose typical for a CT head - 2mSv
False
CT Head = 1.2
The effective dose typical for a CXR 0.15mSV
FALSE 0.1mSV
The effective dose typical for a CT Chest 4 mSV
FALSE. About 6mSV
Barium enema - 7mSv
True about 7 or 8 mSV
Lumbar spine x-rays - 0.8mSv
True Lumbar spine x-rays - 0.8mSv
RADIATION interactions: Biological damage to tissue occurs immediately on interaction with tissue.
False
Following exposure to ionizing radiation, chemical changes occur practically immediately (in seconds to minutes) and then molecular damage (in hours to decades).
Molecular damage to tissue occurs hours after ionising interaction with tissues.
True.
Following exposure to ionizing radiation, chemical changes occur practically immediately (in seconds to minutes) and then molecular damage (in hours to decades).
Chemical changes in tissue occurs hours after ionising interaction.
False.
Following exposure to ionizing radiation, chemical changes occur practically immediately (in seconds to minutes) and then molecular damage (in hours to decades).
The principal radiation sources for medical exposures is x-rays and gamma radiation.
True
Radiation interactions depends on the radiosensitivity of tissues.
Direct ionising radiation damage to tissue occurs by the production of free radicals.
False. INDIRECT.
Direct damage to tissue occurs by the rupture of covalent bonds and indirect damage by the production of free radicals.
Indirect ionising radiation damage to tissue occurs by the rupture of covalent bonds.
False. DIRECT.
Direct damage to tissue occurs by the rupture of covalent bonds and indirect damage by the production of free radicals.
Cell death occurs when there is insufficient time for tissues to recover between subsequent irradiation events.
True.
Free radicals produced secondary to ionization causes chemical changes in tissues.
True.
Biological effects of ionizing radiation is independent of the type of ionising radiation.
FALSE. Depending on LINEAR ENERGY TRANSFER.
Threshold for deterministic effects
Threshold for deterministic effects: Cataract 5 Gy
FALSE.
The most recent guidelines state that the threshold dose for radiation-induced cataracts is 500mSv (0.5Gy)
Threshold for deterministic effects: Temporary Hair Loss 3-4 Gy
True 3-4 Temporary Hair Loss Gy
Threshold for deterministic effects: Erythema 3 - 6 Gy
True. Erythema 3 - 6 Gy
Depression of blood cell production 0.5 Gy
True. Depression of blood cell production 0.5 Gy
Permanent sterility 3-6 Gy
True. Permanent sterility 3-6 Gy
- The potential risks to the foetus from radiation in utero include:
A. Development of cancer
B. Mental retardation
C. Decrease in IQ
D. Intrauterine growth retardation
E. Leukaemia
ALL TRUE.
Max potential for foetal abnormalities received during pregnancy weeks 3 - 8.
True: Weeks 3-8 is the period of organogenesis when the potential is highest.
Mental retardation if max radiation during pregnancy weeks 8 - 15
True: A decrease in IQ is, however, seen up to the 25th week of pregnancy.
Max potential for GROWTH RETARDATION if max radiation given during weeks 8 - 25.
TRUE. Growth retardation weeks 8-25
Max potential for foetal death if max radiation given during 1st Trimester.
FALSE. During pre-implantation phase
Max potential for childhood cancers if max radiation given during 3st Trimester.
FALSE.
The risk is almost nil up to 3 weeks following which the risk remains for the rest of the pregnancy but is maximum in the first trimester.
The risk of fatal cancer from a uniform whole body irradiation is 1 in 200,000 per mSv.
FALSE.
0.005% per millisievert mSv
OR
1 in 20,000 per mSv
The International Commission on Radiological Protection (ICRP) quantifies the radiation risk factor as 5% (5 in 100) per Sv, or 0.005% (1 in 20,000) per mSv.
The risk of developing fatal childhood cancer from irradiation in utero is 1 in 50,000 per mGy.
FALSE.
False: It is 3% per Gy or 1 in 33,000 per mGy. Check
The risk of developing childhood cancer from irradiation in utero is 1 in 10,000 per mSv.
TRUE
The cornea is more radiosensitive than the lens.
False
Radiation dose to the hands of staff arises from the use of radionuclides as well as from x-rays.
True.
Deterministic effects are hereditary.
False.
No, deterministic effects are not considered hereditary; they are tissue reactions that occur directly from a high radiation dose to an individual and do not pass on to their offspring, unlike stochastic effects which can be genetic and therefore heritable
Regarding the natural and artificial sources of radiation:
Sodium is the commonest contributor of radiation from internal sources.
FALSE.
Potassium-40, a radioactive isotope of potassium is the commonest contributor of radiation from internal sources.
The average dose of radiation to the UK population from natural sources is 1.7mSv per year.
FALSE.
Average dose is 2.7mSv per year.
https://www.ukhsa-protectionservices.org.uk/radiationandyou/
Average dose in Cornwall is 7mSv
So just over double the national average of 2.7mSv
True.
The decay of radon is primarily associated with the emission of …
Alpha Particles
The dose received from medical diagnostic procedures averaged over the whole population in the UK is 250µSv.
False: It is 370 µSv and accounts for 14% of the radiation from natural and artificial sources in the UK.
Dose area product (DAP): Decreases with the square of the distance from the x-ray focus.
DAP is absorbed dose x area =
Gy cm^2
INDEPENDANT OF DISTANCE
Dose area product (DAP): Is an appropriate quantity for dosimetry in fluoroscopy.
True
Dose area product (DAP): Is an appropriate quantity for dosimetry in CT.
FALSE.
The quantities used in CT dosimetry include the CT dose index (CTDI), weighted CT dose index (CTDIw), and dose length product (DLP). The effective dose is measured in millisieverts (mSv
Dose area product (DAP): May be used to set diagnostic reference levels.
True. DAP can used to set diagnostic reference levels.
Dose area product (DAP):
Can be measured with a thermoluminescent dosimeter (TLD).
FALSE. Using an ionising chamber!
Entrance surface dose (ESD):
Is measured in Gycm2
False. ESD measured in Gray
Entrance surface dose (ESD): Increases in proportion to x-ray field size.
True. As it includes Scatter.
https://radiopaedia.org/articles/entrance-skin-dose?lang=gb
Entrance surface dose (ESD):
Can be calculated from knowledge of exposure factors and x-ray output data.
TRUE.
Entrance surface dose (ESD):
Can be measured from DAP if the x-ray field size and back scatter are known.
TRUE.
Entrance surface dose (ESD):
Can be measured using a TLD.
TRUE. ESD can be measured using a TLD.
Regarding thermoluminescent dosimeters:
They are generally used in conjunction with filters.
True.
three filters against each disc
top: aluminium and copper
middle: perspex
lower: open
Regarding thermoluminescent dosimeters:
They contain a crystal of lithium iodide.
FALSE.
They contain a crystal of lithium FLUORIDE.
nickel-coated aluminium card with TLD discs
the discs are made of a thermoluminescent material, commonly calcium sulphate doped with dysprosium (CaSO4:Dy) or lithium fluoride (LiF)
Regarding thermoluminescent dosimeters:
They have a linear response over a wide dose range.
True. That’s why we use them/ TLDs!
Regarding thermoluminescent dosimeters:
They can differentiate between radiation types.
FALSE.
TLDs CANNOT differentiate between radiation types.
Regarding thermoluminescent dosimeters:
False. ENTRANCE SURFACE DOSE.
Advantages of thermoluminescent dosimeters: They can measure dose rates.
FALSE.
Advantages of thermoluminescent dosimeters: They can be reused.
TRUE.
Advantages of thermoluminescent dosimeters: The sensitivity is significantly better than film.
FALSE. TLD and Film sensitives are SIMILAR.
Advantages of thermoluminescent dosimeters: They can be used to measure both shallow and deep doses.
True. Hence the different filters?
Advantages of thermoluminescent dosimeters: They can be used to monitor eye doses.
True: TLDs can be made into various shapes, they can be used for the assessment of finger and eye doses.
Film badges: Are able to identify the type of exposure.
TRUE.
Film badges: Utilize a single sided film emulsion.
FALSE. Utilize a DOUBLE sided film emulsion.
Film badges: Are relatively resistant to environmental effects.
False:
FILM BADGES are subject to the environmental effects of HEAT, HUMIDITY, and CHEMICAL CHANGE
Film badges: Utilize a double sided film emulsion with screen.
FALSE. Thy use a double sided film emulsion BUT WITHOUT a screen.
Film badges:
TRUE. TLDs and Film badges HAVE SIMILAR SENISITIVIES.
But unlike TLDs - PERMANENT + NON-REUSABLE.
TLDs can provide a direct reading of dose.
FALSE. INDRECT as LUMINESCENCE
TLDs provide a permanent record of dose.
FALSE. TLDS are TEMPORARY and can be REUSED.
Film badges do not require calibration.
FALSE. FILM BADGES DO REQUIRE CALIBRATION.
Aluminium oxide is used in optical stimulated luminescent dosimeters.
True.
Optical stimulated luminescent dosimeters give readings down to 0.01mSv.
True.
TLDs: Are used for assessment of finger doses.
True.
TLDs: Are relatively cheaper than film badges.
False. TLDs are more expensive but reusable.
TLDs: Are used to detect radioactive contamination.
FALSE.
TLDs: The dose can be read only once.
D. True: They can only read a dose once but TLDs can be re-used and read many times.
TLDs: Are unaffected by environmental effects.
False: They are affected by environmental effects (especially heat).
TLDs: An immediate read out is possible.
FALSE.
TLDs: Sensitivity is relatively energy dependent.
False: TLDs are relative energy independent.
TLD crystal needs to be heated to about 300°C to be read.
True.
TLDs need to be annealed after read out.
True
TLD crystal can be calcium fluoride.
True
Film badges: Sensitivity is about 0.1-0.2mSv.
True.
Film badges: Can be used for assessment of finger dose.
False. TLDs used for finger and eye doses.
Film badges: Provide a permanent record of exposure.
True.
Film badges: Are usually replaced 3 monthly.
False.
Film badges are subject to the environmental effects of heat, humidity, and chemical change
UNSUITABLE OVER 1 MONTH.
Film badges: Measure the effective dose received.
FALSE.
Film badges measure the ABSORBED dose, which we presume represents the whole body dose.
TLDs have a precision better than 1%.
False: Only electronic dosimeters have a precision better than 1%.
TLDs can be used to measure dose to a patient.
TRUE.
Dosimeters: Dose to a patient can be measured with an ionization chamber.
True.
Geiger Muller counters require a quenching agent.
True.
How a Geiger Muller tube works:
When radiation enters the tube, it ionizes the gas inside, creating an avalanche of electrons towards the central anode.
Problem without quenching:
If left unchecked, this avalanche could continue indefinitely, causing a continuous discharge and preventing the detection of further radiation events.
Role of the quenching agent:
A small amount of a special “quench” gas like a halogen or organic vapor is added to the tube, which absorbs the energy released during the avalanche, preventing further ionization and allowing the tube to reset for the next detectio
The outer case of the Geiger Muller counter is the anode.
False: The outer case is the cathode.
Electronic personal dosimeters: Are more than 100 times sensitive than TLDs.
True. On Electronic personal dosimeters have a better than 1% accuracy.
Electronic personal dosimeters:
Measure both dose and dose rates.
True. Electronic personal dosimeters measure BOTH DOSE and DOSE RATES.
Electronic personal dosimeters:
Have sensitivity to the nearest 1µSv.
True.
Electronic personal dosimeters:
Do not provide a direct reading.
FALSE. Electronic personal dosimeters DO provide a direct reading.
Electronic personal dosimeters:
The silicone diode detector is a common type.
True.
TLD should not be used without a dosimeter holder.
True.
During interventional procedures the TLD must be worn above the protective lead apron.
FALSE. KEEP TLD UNDER APRON.
Electronic personal dosimeters are used to detect radioactive contamination.
True.
Electronic personal dosimeters are used to detect radioactive contamination.
The TLD holder helps to differentiate between skin doses and deeper doses.
True.
True: The holder has filters which are responsible for this function.
The precision of a TLD is approximately 15% for low doses.
True.
TLD = 15% for low doses
TLD = 3% for high doses
The precision of a TLD is approximately 3% for high doses.
True.
TLD = 15% for low doses
TLD = 3% for high doses
Geiger Muller tubes:
Have a dead time when no reading can be done.
TRUE.
Geiger Muller tubes:
Are used mainly for patient monitoring.
False: They are used mainly in nuclear medicine to detect contamination.
Geiger Muller tubes: Detect all types of radiation.
True.
Geiger Muller tubes: Can distinguish between all types of radiation.
FALSE.
Can detect ALL types of radiation but CANNOT DIFFERENTIATE between them
Geiger Muller tubes: Contain a central wire cathode.
FALSE.
OUTER HOUSING is the CATHODE
CENTRAL WIRE is the ANODE.
IRR 1999 (99) has been replaced with
Ionising Radiation Regulations 2017
https://www.legislation.gov.uk/uksi/2017/1075/contents
IRMER (2000) has been replaced with
IRMER (2017)
Regarding controlled areas:
Are required where a person working is likely to receive an effective dose more than 3 mSv per year.
FALSE.
IRR 2017:
Regarding controlled areas are required where a person working receives more than:
EFFECTIVE DOSE: 6mSv per year
EQUIVALENT DOSE: 15mSv to LENS
EQUIVALENT DOSE: 150mSv to SKIN or EXTREMETIES
RCA: 6/15/150
RSA: 1/5/50
Radiology controlled areas:
Required with equivalent dose of 15mSv to eye or
150mSv to skin or extremities.
True.
RCA: 6/15/150
RSA: 1/5/50
Radiology Supervised area:
If effective dose is greater than 1mSv per year
True
RCA: 6/15/150
RSA: 1/5/50
Radiology Supervised area:
If equivalent dose is 5mSv to lens or 50mSv to extremities.
True
RCA: 6/15/150
RSA: 1/5/50
Regarding controlled areas:
Dose rate exceeds 7.5 micro Sv per hour averaged over the day.
True.
Regarding controlled areas:
Are required where a person working is likely to receive a radiation dose greater than three-tenths of any dose limit.
True.
An employer is required to designate a person as being classified if that person is likely to receive an effective (whole body) dose in excess of 6mSv/y, or more than three-tenths of the dose limit to the extremities (150 mSv/y).
Regarding controlled areas:
Are required where the external dose rate could exceed 5 µSv per hour averaged over the working day.
FALSE.
Regarding controlled areas:
Dose rate exceeds 7.5 micro Sv per hour averaged over the day.
Regarding controlled areas:
An intervention suite is an example.
True.
Regarding controlled areas:
True.
IRR 2017:
All imaging AND INJECTING ROOMS will be controlled areas due to prevailing dose rates AND RISK OF CONTAMINATION.
Staff exposed to potential contamination should have appropriate PPE.
Ideally hot and cold waiting areas should be separate.
Controlled areas:
Are required where a person working is likely to receive an equivalent dose more than 6mSv per year:
FALSE.
EFFECTIVE dose >6 mSv / year
Controlled areas:
May be required where there is a risk of radioactive contamination.
TRUE.
Controlled areas:
Must be described in the local rules.
TRUE.
Ionising Radiations Regulations 2017 (IRR 2017), “controlled areas” must be - clearly described and outlined
- within the “local rules”
- that an employer is required to establish for radiation protection purposes
- must detail specific procedures and restrictions
Controlled areas:
D. Are permitted areas for pregnant staff.
True.
IRR 2017:
EMPLOYER must take steps to
- minimise radiation exposure,
- with the goal of keeping the equivalent dose to the fetus below 1 millisievert (mSv) for the remainder of the pregnancy
Controlled areas:
Are monitored by the Radiation Protection Advisor
FALSE.
Controlled area:
MONITORING: Radiation protection SUPERVISOR
ENFORCING: Health and Safety Executive (HSE) in most situations, or the Office for Nuclear Regulation (ONR) for nuclear sites
Supervised areas:
Are required only where a person working is likely to receive an effective dose more than 3mSv per year.
FALSE:
IRR 2017:
Are required only where a person working is likely to receive an effective dose more than 1 mSv per year.
The radiation worker dose limit in mSv/year in IRR 2017
The radiation worker dose limit of 20 mSv/year in IRR17
Supervised areas:
Are required only where a person working there is likely to receive a radiation dose greater than three-tenths of any dose limit.
FALSE.
3/10 x 20 = 6 mSv - this is the limit for a controlled area
RSA = 1 mSv per year or 1/20th
Supervised areas:
C. The waiting room for patients who have been injected with a radiopharmaceutical is an example.
True.
Supervised areas:
Must be clearly marked with warning signs.
True.
IRR 2017: RCA and RSA’s:
is adequately described in local rules; and
(b) has suitable and sufficient signs displayed in suitable positions warning that the area has
been so designated a
Supervised areas:
Can become a controlled area.
True: If the dose limits are exceeded and should be monitored regularly.
Regarding IRR 2017:
The employer must consult a Radiation Protection Supervisor prior to installing new equipment.
FALSE.
Radiation protection adviser must be consulted for new equipment.
Regarding IRR 2017:
The Healthcare Commission must be informed of the use of ionizing radiation by the employer.
False.
Ionising radiation use must inform health and safety executive (HSE)
IRR 2017:
Part 2 (General principles and procedures—Regulations 5–13)
Regulation 5 requires certain work with ionising radiation to be notified to the appropriate authority (either the Health and Safety Executive (“the Executive”) or,
where the work relates to
particular nuclear-related sites, the Office for Nuclear Regulation (“the ONR”)).
Regarding IRR 2017:
The Radiation Protection Supervisor (RPS) is invariably a medical physics expert.
FALSE.
Any suitably trained staff member, e.g. radiographer, can take up the role of RPS.
According to the Ionising Radiations Regulations (IRR) 2017, a “Radiation Protection Supervisor” (RPS) can be any individual appointed by an employer to oversee the implementation of local rules and ensure compliance with the IRR 2017 regarding radiation protection within their workplace; this could be a staff member directly involved in radiation work, a team leader, or another suitable person with the necessary training and authority to monitor radiation practices and enforce safety procedure
Regarding IRR 2017:
Critical examination of equipment is the responsibility of the employer.
FALSE. By Installer:
(2) Where a person erects or installs an article for use at work, being work with ionising
radiation, that person must—
(a) undertake a critical examination of the way in which the article was erected or installed
for the purpose of ensuring, in particular, that—
(i) any safety features and warning devices operate correctly; and
(ii) there is sufficient protection for persons from exposure to ionising radiation;
consult with the radiation protection adviser that they appointed, or that the employer
engaged in work with ionising radiation appointed, with regard to the nature and extent of
any critical examination and the results of that examination
Regarding IRR 2017:
The Radiation Protection Supervisor (RPS) must be an employee of the organization.
FALSE. They can be contracted out.
https://www.luciongroup.com/services/radiation-protection-supervisor-contractor-hire/
Regarding IRR 2017:
The regulations govern the safety of staff, patients, and public.
False: The regulations govern the safety of staff and public but not patients.
Regarding IRR 2017:
The Health and Safety Executive is the governing authority.
True.
And for radionculides:
Office for Nuclear Regulation
Regarding IRR 2017:
The local rules should include descriptions of all designated areas.
True.
Regarding IRR 2017:
The equivalent dose limits are concerned with stochastic effects.
FALSE.
EQUIVALENT dose limits are designed to ensure doses are kept below the threshold doses for DETERMINISTIC effects.
Regarding IRR 2017:
The effective dose limits are designed to prevent deterministic effects.
FALSE.
EFFECTIVE dose limits are designed to prevent STOCHASTIC effects (cancer / inheritable effects).
The following annual dose limits apply:
The effective dose to a member of public is 2mSv.
FALSE.
IRR 2017 Whole body EFFECTIVE dose:
Over 18: 20 mSv (same as lens)
Under 18 workers: 6mSv
Public: 1mSv
The following annual dose limits apply:
The equivalent dose to the lens of the eye of an employee is 500mSv.
FALSE.
IRR 2017:
Equivalent dose limits for LENS:
Over 18:
20mSv per year.
OR 100mSv over 5 years, with max 50mSv in any one year.
Under 18 or anyone else:
15 mSv per year
The following annual dose limits apply:
The equivalent dose to the skin of an employee is 500mSv.
TRUE.
IRR 2017:
EQUIVALENT dose to skin:
Over 18: 500 mSv
Under 18 workers: 150 mSv
Public: 50 mSv
The following annual dose limits apply:
The dose to the abdomen of a woman of reproductive age should not be more than 13mSv in any consecutive 3-month period.
FALSE.
IN IR 1999
https://www.legislation.gov.uk/uksi/1999/3232/schedule/4/part/I/made/data.xht?view=snippet&wrap=true
BUT NOT 2017
https://www.legislation.gov.uk/uksi/2017/1075/schedule/3
The following annual dose limits apply:
The equivalent dose to the extremities of an employee is 150mSv.
False. True for only under 18 year olds:
EQUIVALENT dose to skin or extremities:
Over 18: 500 mSv
Under 18 workers: 150 mSv
Public: 50 mSv
The following annual dose limits apply:
The equivalent dose to the skin of a member of the public is 50mSv.
TRUE.
EQUIVALENT dose to skin or extremities:
Over 18: 500 mSv
Under 18 workers: 150 mSv
Public: 50 mSv
The following annual dose limits apply:
The foetus of a pregnant employee should not receive more than 0.1mSv.
FALSE.
A dose constraint of 1mSv is applied as the foetus is regarded as a member of the public.
IRR 2017:
EMPLOYER must take steps to
- minimise radiation exposure,
- with the goal of keeping the equivalent dose to the fetus below 1 millisievert (mSv) for the remainder of the pregnancy
The following annual dose limits apply:
The equivalent dose to the lens of a member of the public is 15mSv.
FALSE.
Equivalent dose limits for LENS:
Over 18:
20mSv per year.
OR 100mSv over 5 years, with max 50mSv in any one year.
Under 18 or anyone else:
15 mSv per year
The following annual dose limits apply:
The equivalent dose to the extremities of a member of the public is 150mSv.
FALSE.
EQUIVALENT dose to skin or extremities:
Over 18: 500 mSv
Under 18 workers: 150 mSv
Public: 50 mSv
The following annual dose limits apply:
The effective dose to an employee is 10mSv.
FALSE.
IRR 2017 Whole body EFFECTIVE dose limit:
Over 18: 20 mSv (same as lens)
Under 18 workers: 6mSv
Public: 1mSv
IRR 17 states that the following people may enter controlled areas:
Classified employees.
True
IRR 17 states that the following people may enter controlled areas:
Radiographers
False.
IRR 17 states that the following people may enter controlled areas:
Non-classified employees entering under a written agreement.
True.
https://assets.publishing.service.gov.uk/media/5fdb807ed3bf7f3a334ed39d/JSP_392Chapter_05-WRITTEN_ARRANGEMENTS__Alt_Text.pdf
IRR 17 states that the following people may enter controlled areas:
Patients having radionuclide imaging.
False.
IRR 17 states that the following people may enter controlled areas:
Operators
False.
Non-classified workers are not permitted to enter controlled areas.
False: Local rules may allow non-classified workers to enter a controlled area.
Controlled areas: Require special working procedures to restrict exposure.
True.
Access of radiology staff to controlled areas must be restricted.
True.
Controlled areas:
Are needed for portable x-ray units.
True.
For mobile X-ray sets, the controlled radiation area extends in the direction of the Xray beam until the beam is sufficiently attenuated by distance (approximately 8 m) or
shielding (e.g. solid floor or wall) and out to 3 m in all other directions
https://assets.publishing.service.gov.uk/media/5fdcc23ee90e07452df92f09/JSP_392Chapter_26-MEDICAL_X-RAY__Alt_Text.pdf
Controlled areas:
Must be clearly marked with warning signs and indicate the nature of the source and risk
True.
The following events must be reported if a patient receives:
15 times the intended dose for a chest x-ray
https://www.cqc.org.uk/guidance-providers/ionising-radiation/ionising-radiation-medical-exposure-regulations-irmer/criteria-making-notification/notification
https://www.radiologyinfo.org/en/info/safety-xray
FALSE.
15 X 0.1 mSv = 1.5mSv
As per CQC:
Intended dose less than 0.3mSv
Criteria for notification:
3mSv or above (adult)
1mSv or above (child)
The following events must be reported if a patient receives:
8 times the intended dose for a mammogram.
https://www.cqc.org.uk/guidance-providers/ionising-radiation/ionising-radiation-medical-exposure-regulations-irmer/criteria-making-notification/notification
https://www.radiologyinfo.org/en/info/safety-xray
FALSE.
Normal mammogram = 0.21 mSv (double a CXR)
8 x 0.21 - 1.6 mSv
As per CQC:
Intended dose less than 0.3mSv
Criteria for notification:
3mSv or above (adult)
1mSv or above (child)
The following events must be reported if a patient receives:
10 times the intended dose for a lumbar spine x-ray.
https://www.cqc.org.uk/guidance-providers/ionising-radiation/ionising-radiation-medical-exposure-regulations-irmer/criteria-making-notification/notification
https://www.radiologyinfo.org/en/info/safety-xray
TRUE.
Lumbar Spine 1.4 mSv
10 x 1.4 m Sv = 14 mSv
Intended dose between 0.3 mSv and 2.5 mSv
so 10 or more = REPORTABLE.
The following events must be reported if a patient receives:
1.5 times the intended dose for a CT abdomen.
https://www.cqc.org.uk/guidance-providers/ionising-radiation/ionising-radiation-medical-exposure-regulations-irmer/criteria-making-notification/notification
https://www.radiologyinfo.org/en/info/safety-xray
FALSE.
Single Phase = 7.7 mSv
Dual Phase = 15.4 mSv
1.5 of single phase = 11.6 mSv
Intended dose between 2.5mSv and 10mSv
Reportable is over 25mSv
1.5 of dual phase = 23.1 mSv
Intended dose more than 10mSv
Reportable 2.5 x or more.
The following events must be reported if a patient receives:
Twice the intended dose for a barium enema.
FALSE.
Intended dose = 6 mSv
2 x 6 = 12mSv
Intended dose between 2.5mSv and 10mSv
Reportable over 25 mSv
The following events must be reported to the HSE:
https://www.cqc.org.uk/guidance-providers/ionising-radiation/ionising-radiation-medical-exposure-regulations-irmer/notify-us-about-exposure
False.
HSE needs to be informed of events secondary to equipment faults; those due to operator errors need to be reported to the Care Quality Commission, previously known as the Healthcare Commission.
When there is an accidental or unintended exposure to ionising radiation, and the IR(ME)R employer knows or thinks it is significant or clinically significant, they must investigate the incident and report it to the appropriate UK IR(ME)R enforcing authority (under Regulation 8(4)).
The following events must be reported to the HSE:
A patient receives 1.6 times the intended dose for an angiogram.
True.
The following events must be reported to the HSE:
Loss of radioactive material.
True
The following events must be reported to the HSE:
Spillage of any amount of radioactive material.
False.
The following events must be reported to the HSE:
A patient receives 1.3 times the intended dose during radionuclide therapy.
False. Reportable to CQC.
Delivered dose to the planned treatment volume or organs at risk is 1.1 or more times (whole course) or 1.2 or more times (any fraction) the intended dose.
According to IRR 2017:
The RPA is responsible for quality assurance.
FALSE.
According to the Ionising Radiations Regulations 2017 (IRR 2017), the employer is solely responsible for ensuring quality assurance when it comes to radiation protection practices in the workplace, including establishing procedures, protocols, and quality assurance programs to manage radiation exposure and comply with regulations; this responsibility encompasses ensuring all necessary equipment is properly tested and maintained.
According to IRR 2017:
The RPS is responsible for designation of radiation areas.
True.
The prime duty of the RPS is to ensure compliance with the IRR17 in respect of work carried out in the designated area – in
According to IRR 2017:
The RPA must be an employee of the organization.
False.
Can be an external consultant.
According to IRR 2017:
The RPA is responsible for supervising staff dose monitoring.
False.
The RPS is responsible for supervising staff dose monitoring.
According to IRR 2017:
The RPS must be consulted prior to the installation of new x-ray equipment.
False.
The RPA must be consulted prior to the installation of new x-ray equipment.
Regarding classified workers:
The annual effective dose limit is 6mSv.
FALSE.
Above 6mSv is what makes them classified.
Annual limit is 20 mSv.
https://www.legislation.gov.uk/uksi/2017/1075/part/5#:~:text=%E2%80%94(1)%20Subject%20to%20paragraph,skin%20or%20the%20extremities%20and
Regarding classified workers:
An employee above the age of 16 years can be classified.
FALSE.
They must be over 18.
https://www.legislation.gov.uk/uksi/2017/1075/part/5#:~:text=%E2%80%94(1)%20Subject%20to%20paragraph,skin%20or%20the%20extremities%20and
Regarding classified workers:
The records of classified workers must be kept for 25 years beyond the date that the individual stops working as a classified personnel.
FALSE.
[CHANGED FROM 50 YEARS!]
Classified worker records should be kept for 30 years since last entry or when they reach 75.
https://www.legislation.gov.uk/uksi/2017/1075/part/5#:~:text=%E2%80%94(1)%20Subject%20to%20paragraph,skin%20or%20the%20extremities%20and
Regarding classified workers:
They must undergo annual health checks.
True.
https://www.legislation.gov.uk/uksi/2017/1075/part/5#:~:text=%E2%80%94(1)%20Subject%20to%20paragraph,skin%20or%20the%20extremities%20and
Regarding classified workers:
Staff working in nuclear medicine are classified workers.
False.
Staff working in nuclear medicine are very rarely required to be classified.
Regarding standards for x-ray equipment:
For portable x-ray equipment the total filtration of the tube and its assembly should not be less than 1.5mm of aluminium.
FALSE.
For portable x-ray equipment the total filtration of the tube and its assembly should not be less than 2.5 mm of aluminium.
Regarding standards for x-ray equipment:
A Leakage radiation from the tube must be less than 1mGy/hr at 1 metre from the focus.
TRUE.
Leakage radiation is the term given to radiation escaping the X-ray tube housing other than
through the tube port. This must be limited to less than 1 mGy hr-1 averaged over an area of
1 m2 at a distance of 1 metre from the focal spot.
https://www-pub.iaea.org/MTCD/publications/PDF/Pub1578_web-57265295.pdf
https://www.bir.org.uk/media/414334/final_patient_shielding_guidance.pdf
https://www.radiologycafe.com/frcr-physics-notes/radiation-dosimetry-protection-and-legislation/radiation-protection/
Regarding standards for x-ray equipment:
Skin entrance dose rates for ftuoroscopy should not exceed 100mGy/min.
True.
Regarding standards for x-ray equipment:
For mobile x-ray equipment the position of the exposure switch should be designed such that the operator can stand at least 1m from the tube and x-ray beam.
False.
About 1.8 - 2m
The installer or RPA can complete the critical examination of new equipment.
True
Farr’s 3rd Ed:
Installer has a duty to check all the critical warning lights and safety features are operational which may be in conjunction with or supervised by the RPA
Tests on all equipment, annually at least, are mandatory.
FALSE.
Just all instruments used for RADIATION PROTECTION SERVICES.
Regulations 20(3) of the Ionising Radiations Regulations 2017 (IRR17) requires that all instruments used for radiation protection purposes for fulfilling the requirements of the Regulations shall be adequately tested and thoroughly examined at appropriate intervals by or under the supervision of a Qualified Person. The Approved Code of Practice (ACoP) recommends the interval to be at least once every year.
https://www.ukhsa-protectionservices.org.uk/radmet/services/legal
Quality assurance:
Requires the equipment used for testing to be calibrated.
True
Quality assurance:
Is not a requirement under IRMER 2017.
FALSE.
“Quality assurance IRMER 2017” refers to the quality assurance procedures required under the Ionising Radiation (Medical Exposure) Regulations 2017 (IR(ME)R), which mandate employers to establish comprehensive quality assurance programs for all aspects of medical radiation procedures, including written protocols, equipment functionality, and practitioner practices, to ensure patient safety and minimize unnecessary radiation exposure
Quality assurance:
Is a requirement under IRR 17
True.
The Ionising Radiations Regulations (IRR) 2017 (IRR17) establish quality assurance measures for radiation protection in the workplace. These measures include:
Regarding dose limits and dose constraint:
Dose limits do not apply to patients.
True.
Regarding dose limits and dose constraint:
The dose limits can be relaxed for comforters and carers.
True.. Depending on local policy.
IRMER 2017:
In the case of regulation 3(d), the employer’s procedures must provide that appropriate
guidance is established for the exposure of carers and comforters.
Regarding dose limits and dose constraint:
A dose constraint is a dose limit of radiation.
FALSE.
Dose constraints
– are not dose limits
– are selected at some fraction of the dose limit
– should be selected based on good practice and on what can
reasonably be achieved
https://www.icrp.org/docs/anne%20mcgarry%20dose%20constraints%20in%20occupational.pdf
Regarding dose limits and dose constraint:
The relaxation of dose limits can routinely be applied to employees.
E. False: They can be relaxed only in cases of emergencies.
According to IRR 2017:
A radiation dose of 30mSv in a single year may be acceptable to a classified worker.
https://www.legislation.gov.uk/uksi/2017/1075/schedule/3
True: As long as the dose received by the individual does not exceed 100mSv over 5 years.
For the purposes of regulation 12(2), the limit on effective dose for employees or trainees of 18 years or above is 100 mSv in any period of five consecutive calendar years subject to a maximum effective dose of 50 mSv in any single calendar year.
According to IRR 2017:
A classified worker is one whose radiation dose is likely to exceed one-tenths of any dose limit.
False.
A classified worker is one whose radiation fse is likely to exceed three-tenths of any dose limit. *
According to IRR 2017:
The RPA is responsible for the review of local rules.
False: This is the responsibility of the Radiation Protection Supervisor:
According to IRR 2017: The RPA can carry out critical examination of equipment.
False.
The RPA should supervise the critical examination performed by the installer.
According to IRR 2017:
An x-ray department can have more than one Radiation Protection Supervisor.
False.
Under IRR 2017:
The RPA may also be a medical physics expert.
True.
Under IRR 2017:
The annual equivalent dose limit to the lens of the eye of a trainee employee under the age of 18 years is 150mSv.
https://www.legislation.gov.uk/uksi/2017/1075/schedule/3
False.
IRR 2017:
Equivalent dose limits for LENS:
Over 18:
20mSv per year.
OR 100mSv over 5 years, with max 50mSv in any one year.
Under 18 or anyone else:
15 mSv per year
Under IRR 2017:
The annual effective dose limit for a trainee employee under the age of 18 years is 6mSv.
TRUE.
IRR 2017 Whole body EFFECTIVE dose limit:
Over 18: 20 mSv (same as lens)
Under 18 workers: 6mSv
Public: 1mSv
Under IRR 2017:
The RPS is responsible for ensuring monitoring equipment is calibrated.
False. The RPA ensures equipment is calibrated.
Under IRR 2017:
To work as a classified person the individual must be certified as being medically fit to work prior to employment.
True.
They must undergo a health check.
An effective dose of 6mSv:
Carries a risk of about 1 in 3000 of a fatal cancer.
True.
Risk of fatal cancer = 1 in 20,000 per mSv
6/20,000
= 3 / 10,000
= 1 / 3333
An effective dose of 6mSv:
Would be excessive for a barium enema examination.
False.
Approximate effective radiation dose for a barium enema is 6mSv anyway!
https://www.radiologyinfo.org/en/info/safety-xray
An effective dose of 6mSv:
Is the annual dose limit for a trainee classified worker.
False: The annual dose limit for trainees is 6mSv, but trainees cannot be classified.
An effective dose of 6mSv:
Is approximately 5 times the annual background radiation dose in the UK.
False. About twice background dose.
UK average annual radiation dose = 2.7 mSv
https://www.gov.uk/government/publications/ionising-radiation-dose-comparisons/ionising-radiation-dose-comparisons
An effective dose of 6mSv:
ls approximately 10 times the effective dose of an AP pelvis radiograph.
TRUE.
The radiation dose for an abdominal radiograph (0.6 mSv)
Under IRMER 2017:
It is binding on the employer to identify the referrer.
True.
Under IRMER 2017:
Only doctors and dentists may act as referrers.
False: Nurse practitioners and physiotherapists may act as referrers (but must be state registered).
Under IRMER 2017:
Radiographers can perform the role of practitioners.
True.
A radiographer can act as an IR(ME)R practitioner to justify the exposure and as an operator to perform the exposure
Under IRMER 2017:
The employer is responsible for ensuring patient doses are as low as reasonably practicable (ALARP).
True.
Meaning they must implement procedures and practices to minimize radiation exposure to patients while still achieving the necessary diagnostic information.
Under IRMER 2017:
A referrer is not liable for prosecution.
False. They must also have knowledge of IRMER.
Regarding Diagnostic Reference Levels (DRLs):
An investigation must be initiated if a patient DRL has been exceeded.
False.
DRLs are not dose limits but guidance for dose levels for typical examinations in standard-sized patients.
Regarding Diagnostic Reference Levels (DRLs):
Can be different for the same examination in different hospitals.
True.
Set locally with input from the medical physics expert.
Regarding Diagnostic Reference Levels (DRLs):
A DRL should be expressed as entrance surface dose.
False.
e:They can be expressed as DAP, kv, mAs, screening time, etc.
Regarding Diagnostic Reference Levels (DRLs):
Local DRLs cannot be higher than national levels.
False: They can be higher if justified on clinical grounds.
Regarding Diagnostic Reference Levels (DRLs):
The national DRL for a chest PA radiograph is 0.2mGy (ESD).
https://www.gov.uk/government/publications/diagnostic-radiology-national-diagnostic-reference-levels-ndrls/ndrl#national-drls-for-general-radiography-and-fluoroscopy
True - ish.
Chest PA 0.15 mGy
Chest AP 0.2 mGy
The following are true under IRMER 2017:
The operator is responsible for justification of an exposure.
False.
The practitioner justifies an exposure.
The following are true under IRMER 2017:
It does not apply to individuals participating voluntarily in a research programme.
False.
The following are true under IRMER 2017:
It does not apply to individuals for pre-employment occupational health assessment.
False.
Training is required for PRACTITIONERS (US) and operators (Radiographers).
The following are true under IRMER 2017:
Referrers need to be trained adequately for requesting radiological investigations.
https://www.gov.uk/government/publications/breast-screening-guidance-on-implementation-of-ionising-radiation-medical-exposure-regulations-2017/guidance-for-the-implementation-of-the-irmer-regulations-2017#training
False.
Under IRMER 2017 the practitioner and operator must be adequately trained.
The referrer must have access to local guidelines and understand requests within the scope of their practice.
The following are true under IRMER 2017:
Preparation of a radiopharmaceutical is the responsibility of the operator.
True.
A radiopharmacist operator, also known as a radiopharmaceutical scientist, prepares radioactive medicines for use in nuclear medicine studies
The following are true under IRMER 2017:
Only a practitioner can justify an exposure.
https://www.gov.uk/government/publications/breast-screening-guidance-on-implementation-of-ionising-radiation-medical-exposure-regulations-2017/guidance-for-the-implementation-of-the-irmer-regulations-2017#justifying-and-authorising-breast-screening-exposures
True.
Justification is the primary role of the IR(ME)R practitioner who must be a registered healthcare professional, such as a radiographer or radiologist. An assistant practitioner may not act as an IR(ME)R practitioner justifying exposures.
The following are true of IRR 2017:
It is mandatory to monitor doses of persons working with radiation.
False. Only classified workers or all other works in CONTROLLED areas.
The following are true of IRR 2017:
In conjunction with the employer the RPS investigates overexposures.
False: The RPA investigates overexposures.
The following are true of IRR 2017:
The employer is responsible for the training of employees.
True.
The following are true of IRR 2017:
Does not allow a trainee below the age of 18 years in supervised and controlled areas.
False.
Trainees are allowed but with lower dose limits.
According to the Ionising Radiations Regulations 2017 (IRR17), trainees working in a “controlled area” must receive specific training and be subject to strict access controls, meaning only authorized individuals with appropriate training can enter such areas, and their exposure to radiation must be carefully monitored and managed by the employer; this is particularly important for trainees under 18 years old due to lower dose limits applicable to them.
The following are true of IRR 2017:
The radiation dose records of classified workers need to be submitted to HSE certified dose record keeping authorities.
True.
Make sure your employees know their dose information is being kept by your ADS and that summaries are held in HSE’s Central Index of Dose Information (CIDI)
https://www.hse.gov.uk/radiation/ionising/doses/index.htm
https://www.ukhsa-protectionservices.org.uk/cms/assets/gfx/content/resource_5101cs48f7d3043b.pdf
Regarding radiation legislation:
MARS 1978 is responsible for the storage and disposal of radioactive substances.
False: MARS is concerned with the administration of radioactive substances.
Regarding radiation legislation:
he organization must hold an ARSAC (Administration of Radioactive Substances Advisory Committee) certificate to carry out nuclear medicine investigations.
True.
ARSAC advises the licensing authorities on applications from practitioners, employers and researchers who want to use radioactive substances on people.
https://www.gov.uk/government/organisations/administration-of-radioactive-substances-advisory-committee
Regarding radiation legislation:
An ARSAC certificate needs to be renewed every 3 years.
False:
An ARSAC licence is usually valid for 5 years and Research ARSAC licences for 2 years.
Regarding radiation legislation:
RSA 1993 is concerned with the protection of the population and environment.
True.
Radioactive Substances Act
1993https://www.legislation.gov.uk/ukpga/1993/12/contents
Regarding radiation legislation:
IRMER requires that the employee ensure that personal protective equipment is properly used.
False: IRMER applies to patients only.
This is a requirement of IRR 2017.
The principle of optimization is that the benefit from radiation exceeds the risks.
False: This is the principle of justification.
Also MPE helps with optimising protocols to achieve lowest possible dose for diagnostically useful imaging.
Following radionuclide imaging a lactating mother must interrupt breast feeding for 5 days.
False: The period of interruption depends on the radiopharmaceutical. Some do not require any interruption.
Side note:
in relation to an EMPLOYEE who is breastfeeding, that employee must not be engaged in any work involving a significant risk of intake of radionuclides or of bodily contamination.
A pregnant patient cannot have radionuclide imaging.
False.
They can as long as benefits outweigh risks.
Optimisation includes quality assurance programmes to ensure equipment performance.
True
E. The HSE must be notified if the wrong patient has undergone an investigation.
False.
CQC must be notified.
https://www.cqc.org.uk/guidance-providers/ionising-radiation/ionising-radiation-medical-exposure-regulations-irmer/notify-us-about-exposure
Females between the ages of 14 and 55 years being exposed to ionizing radiation must be asked about the possibility of pregnancy.
FALSE.
BETWEEN 12-55 years.
https://www.sor.org/getmedia/1d256f96-40cb-4eeb-b120-90fe27daf7e9/Inclusive-Pregnancy-Status-Guidelines-for-Ionising-Radiation_LLv2
Providing post procedure information to patients who have undergone a nuclear medicine investigation comes under the domain of optimization.
True
Radiation weighting factors are measured in Gray.
False. Weighting factors do not have units.
Lead aprons used in interventional radiology are generally 0.35mm lead equivalent.
False: 0.35mm lead equivalent aprons are used for general radiology and 0.5mm for interventional procedures.
12mm of barium will provide the same protection as 1mm of lead.
True.
A 2.5mm lead equivalent filter should be used for routine radiological procedures.
False:
2.5mm ALUMINIUM equivalent filter should be used.
Lead screen panels used in x-ray rooms to protect staff are usually 5mm thick.
False.
X-Ray room panels have 2mm of lead
In fluoroscopy, the scattered radiation to staff from an overcouch tube is less than an undercouch one.
False:
The radiation from an OVERCOUCH tube is MORE than for an undercouch one.
Thyroid collars used in radiology have 0.5mm lead equivalence.
True.
For chest radiography, the film to focus distance should not be less than 30cm.
FALSE.
It should not be less than, 60cm for fixed equipment. 30cm may be permissible for portable units.
A 0.25mm lead apron transmits less than 3% of the radiation.
False
Transmittance of lead equivalent aprons
0.25 mm = 5 %
0.35 mm = 3 %
0.5 mm = 1.5 %
A 0.25mm lead apron transmits 5 % of the radiation.
True.
Transmittance of lead equivalent aprons
0.25 mm = 5 %
0.35 mm = 3 %
0.5 mm = 1.5 %
A 0.35mm lead apron transmits 3% of the radiation.
True.
Transmittance of lead equivalent aprons
0.25 mm = 5 %
0.35 mm = 3 %
0.5 mm = 1.5 %
A 0.5 mm lead apron transmits 1.5 % of the radiation.
True.
Transmittance of lead equivalent aprons
0.25 mm = 5 %
0.35 mm = 3 %
0.5 mm = 1.5 %
The radiation dose rate from air travel is about 4µSv/hr.
True.
The average daily dose from natural background radiation is 6µSv.
True.
A radiologist wearing a lead apron is adequately protected from the primary radiation.
False.
Lead aprons provide protection only from scattered radiation.
The Environment Agency is the enforcing authority for the Radioactive Substances Act 1993.
True
Photons of energy of 40keV react with soft tissues of the body, predominantly by the Compton reaction
True.
At lower photon energies (<30 keV): Photoelectric absorption becomes more dominant.
Bone has a higher effective atomic number than soft tissue for a diagnostic energy range.
True: The approximate mean atomic number of bone is 13.8 and of soft tissue is 7.4.
For a given energy and medium in the diagnostic range the actual linear attenuation coefficient is always higher than the Compton linear attenuation coefficient.
True. LAC = Compton + Photoelectric
The units of the mass energy absorption coefficient are centimetres (squared)/kg.
False. cm2/g or m2 per Kg
The linear attenuation coefficient is the mass attenuation coefficient divided by the density.
False. MAC = LAC / density
Beam quality depends on kV and voltage waveform.
TRUE.
Beam intensity depends on the atomic number of the target, tube current, kV, and kV waveform.
True: Beam intensity is the energy fluence rate.
Total amount of energy per unit area passing through a cross section per unit time.
It depends on mA, Z, and is inversely proportional to the square of the distance from a point source.
Characteristic radiation constitutes a steadily increasing proportion of the total with
increasing kV.
False.
Increasing the kVp above the threshold does not significantly increase the proportion of characteristic radiation relative to bremsstrahlung, as most photons are still generated through bremsstrahlung.
No characteristic K shell radiation is produced from a Tungsten target at kVp 65.
True. Tungsten K edge is 69.5 KeV
After 2.5mm of aluminium filtration, the peak intensity of an x-ray beam occurs about 1/3 of the maximum kVp.
True. 1/3 to 1/2 of maximum kVp
For a monochromatic xray beam attenuation is exponential.
True: Assuming the x-ray beam is traversing a homogenous medium.
The amount of x-ray attenuation increases as electron density increases.
True: As electron density increases, more photons are attenuated.
Throughout the range of 20-100keV a greater proportion of interactions are photoelectric for soft tissue as compared to bone.
False. MORE FOR BONE.
The unit of mass attenuation coefficient (MAC) is grams per cm squared.
FALSE cm2/g or m2/Kg
The half value thickness is the thickness of a substance that will reduce the intensity of a beam by 50%.
True.
The mass attenuation coefficient: A Is defined as the linear attenuation coefficient (LAC) divided by the density.
True: MAC= LAC/density.
The mass attenuation coefficient: Is affected by the atomic number.
False.
The mass attenuation coefficient is considered to be largely independent of atomic number,
as it is normalized by the density of the material, meaning it represents the attenuation per unit mass rather than per unit volume, which is where the atomic number dependence primarily lies;
this is particularly true for Compton scattering, the dominant interaction mechanism at higher photon energies, where the electron density (electrons per gram) is nearly constant across most elements, excluding hydrogen.
The mass attenuation coefficient: Is directly proportional to the half value layer (HVL).
False:
HVL = 0.69/LAC
MAC = LAC / density
LAC is proportional to MAC then
MAC is INVERSELY proportional to HVL.
The mass attenuation coefficient: Is inversely proportional to the radiation energy.
False: This is only the case for elastic scattering (all energies) and Compton interactions involving photons >100keV.
The mass attenuation coefficient: Depends on the type of radiation interaction.
True
Concerning the Compton effect: There is interaction between a free electron and a photon
True.
Concerning the Compton effect: For incident photons of equal energy, more energy is lost from the photon as the scatter angle increases.
True.
Concerning the Compton effect: High energy radiation undergoes more scattering events than lower energy radiation.
True.
Concerning the Compton effect: The amount of scattering that occurs depends on the electron density of the scattering material.
True.
Electron Density: This is the number of electrons per unit mass or volume of the material.
The photon interacts with individual electrons, not with the entire atom or nucleus.
The atomic number (Z) and atomic structure have minimal influence, as Compton scattering involves electrons that are effectively free or loosely bound.
Concerning the Compton effect: The larger the angle through which the photon is scattered, the more energy it loses.
True: As the angle of scatter of a photon increases, more energy is lost from the photon.
Compton interactions tend to reduce the contrast in the image because: The mean photon energy is reduced.
False. The recoil electron does not leave the object being imaged and does not directly affect the detector.
Compton interactions tend to reduce the contrast in the image because: The photon undergoes a change in direction.
True.
Compton interactions tend to reduce the contrast in the image because: Attenuation of the beam is increased.
False. Compton scattering contributes to attenuation, but it does not necessarily reduce image contrast in this context.
Compton interactions in the screen reduce contrast.
False
Scattered radiation reaching the film would be expected to be reduced by:
A A high tube kV.
B. A moving grid.
C. Coning.
D. Using tubes with higher heat rating.
E. Placing a thin sheet of zinc on the film cassette.
Scattered radiation reaching the film would be expected to be reduced by:
A A high tube kV - FALSE
B. A moving grid- FALSE
C. Coning - Collimation reduces scatter
D. Using tubes with higher heat rating. False Irrelevant
E. False. Not effective. Zinc does not effectively absorb scattered radiation. Scattered radiation is primarily addressed by grids or beam collimation (coning), not by placing materials like zinc directly on the film.
With a parallel grid, cut-off limits the maximum field size.
True. Grid cut-off can indirectly affect the maximum field size in a radiographic image, as it causes a loss of signal at the periphery of the image due to the grid absorbing primary radiation at the edges, effectively limiting the usable field size you can capture without significant image quality degradation; therefore, to avoid cut-off, you might need to slightly reduce the field size to stay within the grid’s effective area.
With a focused grid, cut-off limits the range of focus to film distance.
True.
In a focused grid, the lead strips are angled to match the divergence of the X-ray beam. Cut-off refers to the phenomenon where X-rays that are outside the optimal range of angles (too far from the focal distance) are absorbed by the grid. This results in reduced exposure to the film in areas outside the focused distance, effectively limiting the range of focus to film distance.
A linear grid reduces contrast in the direction perpendicular to the lead strips.
False.
A linear grid has lead strips aligned in one direction (usually horizontally or vertically). It does not inherently reduce contrast in the perpendicular direction. What a grid does is primarily reduce scattered radiation and improve image contrast by absorbing scattered photons, which generally improves contrast in all directions rather than reducing it in a specific direction.
Use of a grid may increase patient dose by a factor of 4.
False.
A grid absorbs a portion of the X-ray beam, which can lead to a need for higher exposure to maintain image quality, but the increase in dose is usually in the range of 1.5 to 2 times the dose without a grid, depending on the type of grid and the technique used.
Grid lines in an image occur only if a stationary grid is used.
False.
Grid lines can occur with both stationary and moving grids. A stationary grid will have visible lines on the image because it doesn’t move, while a moving grid (such as a Bucky grid) moves during exposure to blur the grid lines. However, if the grid movement is not sufficient or if the exposure time is too short, grid lines can still appear.
In the use of grids:
The interspaces may be filled with aluminium.
True: Usual interspace materials are plastic, carbon fibre, or aluminium.
In the use of grids: The grid ratio is defined as the ratio between the height of the lead strips and the distance between them.
The grid ratio is the ratio between the height of the lead strips and the distance between the lead strips.
In the use of grids: The interspaces are usually much thicker than the lead strips.
True.
In the use of grids: In the linear grid it may be possible for the x-ray tube to be angled without the effect of ‘grid cut-off’.
True. The X-ray tube can be angled along the length of the grid lines without causing “grid cut-off” because the lead strips are parallel to the direction of the potential angle, allowing the primary beam to pass through without being blocked by the grid strip
In the use of grids: A crossed grid is made of two superimposed linear grids having different focusing distances.
False:
A crossed grid is two stationary grids superimposed with their grid lines at right angles to each other.The radiation must pass though a tunnel rather than just a channel. Crossed grids require higher exposure and careful centring. If the grids are not at right angles an artefact called Moire fringes may be visualized on the film.
Use of a grid normally leads to:
A Reduced scatter dose to the patient.
False. The patient gets the same or more scatter due to the higher dose needed when using a grid.
Use of a grid normally leads to:
An increase in the exposure latitude of the film screen combination.
False. Exposure latitude refers to the range of exposures that produce acceptable image quality, and grids generally narrow the acceptable exposure range because they absorb some of the primary beam, requiring a higher dose to achieve the desired image quality.
Use of a grid normally leads to: An increase in the exposure to the patient.
True: More x-rays are needed to obtain the same film density when a grid sits between the film and the patient.
Use of a grid normally leads to: A higher mean energy of the beam reaching the film.
True:The beam becomes more penetrating as lower energy scattered radiation cannot reach the film.
Use of a grid normally leads to: A reduction of scatter radiation reaching the film.
True
A focused grid: May cause radiation cut-off at large field sizes.
False.
A focused grid: Should be used within a defined range of focus to film distance.
True. A focused grid is designed to work optimally within a specific range of focus-to-film distances. Outside this range, the X-ray beam may not match the angle of the lead strips, leading to inefficiency and potential cut-off.
A focused grid: Requires an increase in patient dose to achieve the same film density as an exposure without a grid.
True. The use of a grid reduces the amount of X-rays reaching the film (due to the absorption of scattered radiation), so to achieve the same film density or image quality, the exposure must be increased, resulting in a higher patient dose.
A focused grid: Reduces geometric distortion of the image.
False. A focused grid does not affect geometric distortion. Geometric distortion is mainly influenced by the positioning of the X-ray tube, the object being imaged, and the alignment of the film or detector. Grids are used to reduce scattered radiation and improve image contrast, but they don’t reduce geometric distortion.
A focused grid: Improves contrast by reducing the amount of scattered radiation reaching the film.
TRUE.
X-ray exposure to the patient may be reduced by:
Adding a 2mm aluminium filter to the beam.
TRUE.
Adding a 2mm aluminium filter to the beam.
True. Adding an aluminium filter to the X-ray beam helps reduce the exposure to the patient by filtering out low-energy photons that contribute to patient dose but don’t contribute much to the image quality. These low-energy photons are more likely to be absorbed by the patient’s tissues rather than reaching the film or detector. By filtering them out, the beam becomes “harder” (higher average energy), which reduces patient exposure.
X-ray exposure to the patient may be reduced by:
Using a higher kVp.
FALSE. Higher kVp also increases the amount of scattered radiation.
X-ray exposure to the patient may be reduced by:
Reducing the x-ray target-object distance.
False. Reducing the target-object distance (or the distance between the X-ray tube and the patient) increases the patient dose. This is because the intensity of the X-ray beam is inversely proportional to the square of the distance (Inverse Square Law).
X-ray exposure to the patient may be reduced by:
Using rare earth screens.
True. Rare earth screens such as gadolinium oxysulphide are more efficient that calcium tungstate, therefore less x-rays are needed for the same image.
The downside of this is that noise is increased as fewer photons contribute to the image.
X-ray exposure to the patient may be reduced by:
Using a Potter-Bucky grid.
False: A Potter-Bucky grid is the term used to describe the moving grid assembly.
Secondary radiation grids: Usual grid ratio is 4:1-16:1.
A.
B.
C.
D.
E.
True.
Secondary radiation grids: As grid height increases, resolution of the image improves.
True: As grid height increases, more scattered radiation is stopped and resolution improves. However, primary radiation is also stopped and so a higher dose is incurred.
Secondary radiation grids: Grid factor is the ratio of incident radiation to transmitted radiation.
True. The grid factor refers to the ratio of the radiation that passes through the grid (transmitted radiation) to the incident radiation (radiation that hits the grid).
Secondary radiation grids: They absorb both primary and secondary radiation.
FALSE.
Grids are specifically designed to absorb secondary radiation (scattered radiation) while allowing primary radiation (the useful X-ray beam) to pass through.
Secondary radiation grids: Grid ratio is the ability of the grid to stop primary radiation.
False. The grid ratio refers to the height of the lead strips relative to the distance between them
Grid factor is the ratio of incident radiation to transmitted radiation.
The focal spot of the x-ray tube:
Is the cause of the penumbra on the image.
True. The focal spot is indeed the cause of the penumbra (the blurred edges) on an image. The penumbra is created because the X-rays emitted from different parts of the focal spot strike the object and detector at different angles, leading to a blurred boundary. A smaller focal spot size helps reduce the penumbra, improving image sharpness.
The focal spot of the x-ray tube:
Focal spot motion causes motion unsharpness.
True: Any motion of the x-ray tube components or patient contributes to motion unsharpness.
The focal spot of the x-ray tube:
Causes absorption unsharpness.
False. Absorption unsharpness occurs when parts of the X-ray beam are absorbed by tissues or the image receptor unevenly, not as a result of the focal spot. The focal spot is related to geometric unsharpness (such as penumbra), not absorption unsharpness.
The focal spot of the x-ray tube:
Emits radiation of uniform intensity across its face.
False. Hence Anode Heel Effect.
The focal spot of the x-ray tube:
Significantly influences the degree of magnification of objects about the size of the focal spot.
False. The focal spot size does not significantly influence the degree of magnification. Magnification in radiology is more influenced by the distance between the object and the image receptor and the target-object distance, rather than the focal spot size. A larger focal spot may slightly increase geometric unsharpness but doesn’t cause significant magnification changes.
Regarding the focal spot:
Its size increases with an increase in the tube current.
False.
Regarding the focal spot:
Its resolving capacity can be measured by pinhole imaging.
False: Resolution is measured with a star test pattern. Focal spot size is measured with pinhole imaging.
Regarding the focal spot: Its size increases with increased kVp.
False. No impact.
Regarding the focal spot: The focal spot is shorter when measured at the cathode end than at the anode end.
False.
Regarding the focal spot:
A focal spot has improved resolving power if it has a centrally peaked radiation intensity distribution.
True.
A focal spot with a centrally peaked radiation intensity distribution typically has improved resolving power. This means that most of the radiation is emitted from the center of the focal spot, where the intensity is highest, resulting in sharper images and improved resolution. A uniform or central peak distribution reduces geometric unsharpness and enhances image quality.
The effective focal spot is governed by:
The target angle.
The target size.
The line focus principle.
The filament size.
The applied kV.
The effective focal spot is governed by:
The target angle. T
The target size. F
The line focus principle. T
The filament size. T
The applied kV. F
Concerning the ‘air-gap’ technique:
False: Scatter is not removed.The scatter that misses the film does not contribute to the image but scatter which does not lie obliquely contributes to the image.
Concerning the ‘air-gap’ technique:
An air gap of more than 30cm is needed.
True: With a gap of less than 30cm, too much scatter reaches the film to be a valued technique.
Typically, an air gap of around 30-40 cm (12-16 inches) is used in the air-gap technique to effectively reduce scatter radiation.
Concerning the ‘air-gap’ technique:
This technique is equivalent to using a grid, but a higher patient dose is needed.
False. The air-gap technique can reduce scatter radiation similar to how a grid works, but it does not necessarily require a higher patient dose compared to using a grid. In fact, the air-gap technique can often result in a lower patient dose because it avoids the additional dose increase typically required when using a grid to compensate for the loss of primary radiation.
Concerning the ‘air-gap’ technique:
Grids are used in preference to an air-gap technique when imaging paediatric patients.
False: Grids are not used on paediatric patients due to the need for a higher exposure.
Concerning the ‘air-gap’ technique:
An air gap requires increased patient dose.
True.
Higher mA or kVp is needed to maintain photon flux.
Regarding tomography:
The x-ray tube and cassette move in opposite directions.
True.
Regarding tomography:
A large swing angle gives a thicker slice.
FALSE.
Slice thickness inversely proportional to the tomographic angle.
A larger swing angle means the x-ray tube moves over a greater arc, and this results in a more focused and narrower area being captured in the plane of interest. This makes the slice thinner and more precise, with less blurring of surrounding structures.
Regarding tomography:
Blurring is used as an advantage.
C. True: Peripherally, tissues are blurred with the object of interest in focus. However this reduces contrast.
Regarding tomography:
This technique is often used in intravenous urography.
False. Tomography is generally not used in intravenous urography (IVU). IVU typically uses conventional radiography or CT scans for visualizing the urinary system.
Regarding tomography:
Increasing focus-film distance increases slice thickness.
True.
Increasing focus-film distance increases slice thickness = leads to more magnification.
Regarding tomography:
The contrast is dependent on the slice thickness.
True. Thinner slices = less scatter
Regarding tomography:
Only structures at right angles to the film appear sharp.
False: Structures at right angles appear more blurred than those parallel to the film.
Regarding tomography:
Tomography is most useful when imaging structures with low inherent contrast.
True.
It can differentiate between tissues with subtle density differences by taking multiple X-ray projections from different angles, allowing for better visualization of soft tissues that might be difficult to see on a standard X-ray
Regarding tomography:
Image unsharpness is unaffected by the use of tomography.
False.
Image unsharpness is affected by the use of tomography, especially outside the focal plane. The whole point of tomography is to intentionally blur the unimportant structures outside the focal plane, but this creates unsharpness for those areas. The unsharpness is an inherent feature of tomography and is used to enhance the sharpness of the focal plane.
Regarding tomography: Patient dose is higher than in conventional radiography.
True.
Patient dose is typically higher in tomography compared to conventional radiography because the technique requires multiple exposures to create a slice, and the radiation is often spread over a larger area to cover the entire focal plane. This results in a higher overall dose compared to a single exposure in conventional radiography.
When using a narrow angle in tomography:
The section thickness increases.
True. A narrow angle results in a thicker section (slice). This is because a smaller swing angle means that the x-ray tube moves over a smaller arc, which leads to a larger portion of tissue being included in the focal plane. As a result, the slice thickness increases.
When using a narrow angle in tomography:
Tissue contrast is reduced.
True. With a narrow angle, there is less precise separation of the region of interest from surrounding structures. The blurring of structures outside the focal plane is less pronounced, meaning that more tissue is included in the slice, and the resulting image has reduced contrast because the tissues of interest are mixed with surrounding structures.
When using a narrow angle in tomography:
The blurring of structures outside the focal plane is increased.
False. A narrow angle leads to less blurring of structures outside the focal plane.
In contrast, a wider angle produces greater blurring, making the surrounding structures more indistinct. The blurring of structures outside the focal plane is reduced when using a narrow angle.
When using a narrow angle in tomography:
The unsharpness within the focal plane is increased.
False: Decreased.
When using a narrow angle in tomography:
The tendency for phantom image formation increases.
True. This can be compensated for by using multidirectional tomography.
In an x-ray tube, a rotating anode:
Results in a larger focal spot.
Increases the maximum tube rating.
Allows larger exposures to be made when compared with a stationary anode.
Results in a larger focal spot. False
Increases the maximum tube rating. True
Allows larger exposures to be made when compared with a stationary anode. True
A stationary anode allows only slow heat removal by conduction, restricting the maximum exposures that can be made. Stationary anode tubes are only used now for intra-oral dental sets and some mobile units.
In an x-ray tube, a rotating anode:
Reduces heat input to the x-ray tube.
False. The rotating anode does not reduce heat input; it increases heat input compared to a stationary anode. However, it improves heat dissipation by spreading the heat over a larger surface area.
In an x-ray tube, a rotating anode:
Is constructed from molybdenum with a tungsten target.
E. False:The anode can be made from rhodium and the target from both molybedenum or rhodium in mammography.
In x-ray tubes, the anode typically uses tungsten as the target material due to its high atomic number (Z = 74), which makes it very efficient for x-ray production. Tungsten also has a high melting point, which helps with heat dissipation during the rapid energy release in x-ray production.
However, rhodium (Z = 45) is sometimes used in specific medical imaging contexts, especially in mammography. For mammography, the anode material may be rhodium or molybdenum instead of tungsten.
In a rotating anode x-ray tube:
The anode stem is made of tungsten.
The effective focal spot size depends on the anode angle.
Heat is removed from the anode mainly by thermal conduction.
Heat is removed more efficiently when a low current is used.
The anode heel effect occurs in a direction parallel to the anode-cathode axis.
The anode stem is made of tungsten. False
False: It is made of molybdenum which is a poor thermal conductor.
The effective focal spot size depends on the anode angle. True.
Heat is removed from the anode mainly by thermal conduction. False: Heat is lost mainly by radiation. It cannot be removed by convection as the rotating anode lies within a vacuum.
Heat is removed more efficiently when a low current is used. True: A lower current generates less heat at the anode, allowing for better heat dissipation and preventing excessive buildup on the anode surface.
The anode heel effect occurs in a direction parallel to the anode-cathode axis. True
Filtration of the x-ray beam:
In the patient is known as inherent filtration.
Tends to increase tissue contrast.
Would be expected to decrease the maximum photon energy.
Filtration of the x-ray beam:
In the patient is known as inherent filtration. False. Filtration by XR tube
Tends to increase tissue contrast. False. Beam hardening reduces contrast.
Would be expected to decrease the maximum photon energy. False: Maximum photon energy stays the same - filtration preferentially filters lower energy photons that results in a higher mean energy.
Helps to decrease the amount of loading on the x-ray tube.
Filtration of the x-ray beam:
Aluminium is more efficient than copper for filtering off higher energy radiation.
False: Aluminium atomic no is 13 and copper is 29 so copper attenuates x-rays more by photoelectric effect.
Think flimsy Al foil Vs big copper pipe!
Filtration of the x-ray beam:
Helps to decrease the amount of loading on the x-ray tube.
True. By removing these ineffective x-rays, the beam becomes “harder”, meaning it has higher energy and better penetration, which improves image quality.
“X-ray tube loading” refers to the amount of heat generated within an X-ray tube during operation
Inherent filtration:
The glass envelope is responsible for most of it.
True: Inherent filtration is the combined filtration of the window of the tube housing, the insulating oil, the glass insert and the target material itself.
Inherent filtration:
It varies approximately between 0.5 and 1mm of aluminium equivalent.
True. Inherent filtration typically provides 0.5 to 1.0 mm of aluminum equivalent. This range represents the total amount of filtration (including the glass envelope, oil, and other internal components) that filters out lower-energy x-rays from the beam.
Inherent filtration:
Decreases tissue contrast.
True. Beam hardening reduces contrast.
Inherent filtration:
Beryllium has an atomic number of less than 10.
True: Beryllium has an atomic number of 4 and is used where inherent filtration must be minimized, e.g. in mammography.
Inherent filtration:
It includes the oil surrounding the tube.
True. The total amount of filtration (including the glass envelope, oil, and other internal components) that filters out lower-energy x-rays from the beam.
The effective focal spot used in fluoroscopy is usually less than 1mm.
True.
The effective focal spot used in fluoroscopy is usually 0.5 - 1mm.
The intensity of the x-ray beam is greatest when perpendicular to the incident electron beam.
True - No Anode angle!
A tungsten-rhenium alloy does not roughen with use as much as a pure tungsten anode.
True: Rhenium is added to prevent cracking of the TUNGSTEN anode.
The thermal rating of the tube increases as the kV is increased.
False. Decreases.
The maximum photon energy in the spectrum of x-rays from an x-ray set is influenced by:
The peak tube potential (kV).
Filtration.
Tube current (mA).
Target material.
The tube potential waveform.
The peak tube potential (kV) only!!
NOT:
Filtration.
Tube current (mA).
Target material.
The tube potential waveform.
X-ray film density refers to
the degree of blackening or darkness of the developed radiographic film. It is a measure of how much light is transmitted through the film after exposure and development. The greater the film density, the darker the film appears.
If on taking an x-ray, the exposure (mAs) is set to keep the film density constant, then:
An increase in tube potential (kV) will reduce the effective dose to the patient.
True: As mAs decreases.
If on taking an x-ray, the exposure (mAs) is set to keep the film density constant, then:
Using a faster film screen combination will reduce the effective dose to the patient.
True. A faster film-screen combination has greater sensitivity to radiation, meaning it requires less exposure (lower mAs) to achieve the same film density. As a result, less radiation is required, reducing the effective dose to the patient.
If on taking an x-ray, the exposure (mAs) is set to keep the film density constant, then:
Selecting a smaller focal spot will not affect the patient dose.
True. The size of the focal spot mainly affects image sharpness and resolution, not the patient dose. A smaller focal spot provides better resolution, but it does not increase the dose. The dose is more directly influenced by factors like mAs, kV, and filtration
If on taking an x-ray, the exposure (mAs) is set to keep the film density constant, then:
Increasing the x-ray field size will increase effective dose to the patient.
True!
If on taking an x-ray, the exposure (mAs) is set to keep the film density constant, then:
Increasing the exposure time might result in increased patient dose.
True!
The thermal rating of an x-ray tube used in diagnostic radiology:
Is limited by the maximum allowable filament current at high kV.
FALSE. TUBE Current is limited not Filament current.
XRay Tube rating
Tube ratings are the defined input parameters (kVp, mA, exposure) that can be safely used during its operation without causing damage to the x-ray tube itself and unique to each individual x-ray tube model. An x-ray tube rating is the maximum allowable kilowatts (kW) in 0.1 second 2.
The thermal rating of an x-ray tube used in diagnostic radiology:
Is greater when operated at full-wave rectification compared to half-wave at an exposure of 0.1 sec.
FALSE. Full wave rectification = higher tube current = more heating
The thermal rating of an x-ray tube used in diagnostic radiology: Is influenced by anode angle.
True. Larger angle = larger spread of electron beam and subsequent heating
The thermal rating of an x-ray tube used in diagnostic radiology: Increases if the speed of rotation decreases.
False. Slower heat dissipation.
The thermal rating of an x-ray tube used in diagnostic radiology:
Is, with respect to multiple exposures, dependent on the weight of the anode.
True:
Anode Mass and Heat Capacity: The weight (mass) of the anode directly influences its heat capacity—that is, how much heat it can absorb and dissipate without sustaining damage. A heavier anode can absorb and store more heat, which is especially important during multiple exposures or continuous operation. This means that the x-ray tube with a heavier anode has a higher thermal rating and can handle more exposures before reaching its thermal limit.
- Regarding x-ray tube ratings:
Only thermal ratings are important.
FALSE.
While thermal ratings are crucial in determining how much heat an x-ray tube can handle, they are not the only important ratings.
Electrical ratings (e.g., tube voltage, current) and mechanical ratings (e.g., anode speed) are also critical in ensuring the tube operates safely and effectively.
Regarding x-ray tube ratings:
During screening, the heat capacity of the tube housing limits the maximum tube current at a given kVp.
False:
The anode heat storage capacity is the limiting factor.
The tube housing heat capacity is much higher.
Regarding x-ray tube ratings:
At very short exposures, three phase rectified x-ray tubes are rated higher than full-wave rectified tubes.
True.
At very short exposure times, three-phase rectified x-ray tubes generally have higher ratings compared to full-wave rectified tubes because of the significantly lower voltage ripple in three-phase systems, allowing for higher instantaneous power delivery during short exposures
Regarding x-ray tube ratings:
When multiple short exposures are taken, more heat may arise from the anode motor than from x-ray production.
True.
During multiple short exposures, especially in rapid succession, the rotating anode motor can generate more heat than the x-ray production itself. This is because the motor, which is responsible for rotating the anode, requires energy, and that energy is dissipated as heat. This is especially noticeable in high-speed rotations.
Regarding x-ray tube ratings:
A rotating anode has improved efficiency of heat production compared with a stationary anode.
False: Regardless of the type of anode, the efficiency of heat production is largely similar - with over 99% of energy lost as heat.
The heat rating of an x-ray tube:
Decreases as the kV is increased.
True. Increasing kV increases tube current.
The heat rating of an x-ray tube:
Increases as exposure time is lengthened.
False. It gets hotter with longer exposurese.
The heat rating of an x-ray tube:
Is greater for a high speed anode.
True.
The heat rating of an x-ray tube:
Is greater for a stationary anode than for a rotating one.
False. Faster heat dissipation with rotation.
The heat rating of an x-ray tube:
Increases with an increase in effective focal spot size.
When you increase anode angle - you increase actual focal spot size = larger surface area to dissipate heat.
Regarding intensifying screens:
The light production efficiency of a calcium tungstate intensifying screen is 5%.
True: Light production efficiency of a calcium tungstate screen is only 5%, while rare earth screens are better at 20%.
Regarding intensifying screens:
Calcium tungstate emits blue light.
True.
Regarding intensifying screens:
They emit electrons when bombarded with x-rays.
True: Intensifying screens are fluorescent and emit light when x-rays strike. However, they also emit electrons because x-rays undergo Compton scatter and photoelectric absorption in detector materials.
Regarding intensifying screens:
The intensification factor is not related to patient dose.
False: As intensification factor increases, the dose needed to produce an adequate image reduces.
Regarding intensifying screens:
Shorter exposures can be used.
True: Thus minimizing movement unsharpness.
When x-rays are generated at 50kV using a tungsten target and aluminium filter:
The maximum photon energy will be 50keV.
True: The given kV for a tube describes its maximum photon energy. The maximum photon energy cannot be above this.
When x-rays are generated at 50kV using a tungsten target and aluminium filter:
The spectrum will have its maximum intensity at 50keV.
False: Remembering the characteristic x-ray spectrum, the mean photon energy is usually about a third of its maximum energy.
When x-rays are generated at 50kV using a tungsten target and aluminium filter:
Characteristic radiation from the tube is NOT present in the radiation emitted from the tube.
True: Characteristic radiation only occurs when the photon energy is high enough.
Tungsten K edge 69.5 keV
When x-rays are generated at 50kV using a tungsten target and aluminium filter:
X-ray output (dose per mAs) will be decreased if the filter thickness is increased.
True: If filter thickness increases, more low energy photons are removed from the beam, therefore the area under the curve decreases.
When x-rays are generated at 50kV using a tungsten target and aluminium filter:
The K-edge of the filter is important in shaping the x-ray spectrum.
Tungsten K edge 69.5 keV. As energy below k shell binding energy - irrelevant as a K edge filter.
Radiographic contrast would increase if:
kV is increased
False: Scatter increases with increased kV therefore reducing contrast.
Radiographic contrast would increase if:
Compression is applied.
True: Thinner section of tissue is imaged so less scatter is produced giving improved contrast.
Radiographic contrast would increase if:
A grid is used.
True: Reduces scatter reaching the film, improving contrast.
Radiographic contrast would increase if:
Field size is limited.
True: Reduced field size therefore reduces scatter.
Radiographic contrast would increase if:
mAs decreases
False :As mAs decreases, radiographic contrast reduces.
In radiography, image unsharpness may be affected by
Geometric magnification.
Focal spot size.
Both True
The following factors would be expected to lead to a loss of sharpness in a film screen system: A shorter exposure time
False: This reduces motion unsharpness
The following factors would be expected to lead to a loss of sharpness in a film screen system: Increased focal spot size
True: Increased focal spot size increases geometric unsharpness.
The following factors would be expected to lead to a loss of sharpness in a film screen system: Increased magnification.
True: Magnification increases geometric unsharpness.
Geometrical unsharpness is influenced by:
Focus-film distance.
Focal spot size.
The thickness of the patient
The object-film distance.
Focus-film distance. True
Focal spot size. True - Changes penumbra
The thickness of the patient. False Affects contrast but not unsharpness.
The object-film distance. True
Unsharpness will be masked by low contrast.
True: Unsharpness is more noticeable when there is high contrast.
Geometric unsharpness is reduced by keeping magnification as low as possible.
True.
Motion unsharpness may be caused by tube movement.
True.
Comparing x-ray mammography with conventional film screen radiography:
X-rays with a lower mean photon energy are used.
True: Tube maximum is 35Kv.
Comparing x-ray mammography with conventional film screen radiography:
A shorter focus-film distance is used.
True: 65-66cm FFD.
Comparing x-ray mammography with conventional film screen radiography:
Shorter exposure times are used.
False: Longer since kV is low mAs must increase for an adequate image.
Comparing x-ray mammography with conventional film screen radiography:
A larger focal spot is used.
False: Normal radiography uses a 1mm focal spot, mammography uses less than 0.3mm.
Comparing x-ray mammography with conventional film screen radiography:
An anti-scatter grid is less likely to be used.
False: Moving grids are used.
In a mammographic x-ray set with a molybdenum target:
B. The typical tube potential for mammographic exposures is about 35kV.
False. Typical range for mammography is 24-32kV
In a mammographic x-ray set with a molybdenum target:
The x-ray spectrum is generally dominated by characteristic radiation.
True: A molybdenum filter removes part of the continuous spectrum.
In a mammographic x-ray set with a molybdenum target:
The anode does not rotate.
False. The Anode rotates.
In a mammographic x-ray set with a molybdenum target:
The radiation detector for the automatic exposure control is between the grid and the cassette.
False: The AEC sits in front of both the grid and the cassette.
In a mammographic x-ray set with a molybdenum target:
The filter may also be molybdenum.
True: Combinations include MoMo,TRh, MoRh.
When compression is used in mammography:
It reduces the dose to the breast.
True: The tissue thickness being imaged is reduced so scatter is reduced, thus reducing dose.
When compression is used in mammography:
It reduces the proportion of scattered radiation reaching the film screen.
True.
When compression is used in mammography:
Its prime purpose is to immobilize the patient.
False: To reduce thickness / scatter.
When compression is used in mammography:
It reduced the total volume of the breast.
False: The volume of the breast cannot be changed.
When compression is used in mammography:
he applied force must be less than 50N (5kg force)
Foce applied during a mammogram typically ranges between 100 and 200 Newtons (N)
10-20Kg
Mammography:
Maximum image contrast is obtained at photon energies of 50-60keV.
False: Lower keV is used with maximum tube voltage of about 30keV.
Mammography:
The characteristic radiation of a molybdenum target occurs at 17.5 and 19.5 keV.
True.
The characteristic radiation of a molybdenum target occurs at 17.5 and 19.5 keV.
Mammography:
The molybdenum filter attenuates the characteristic radiation produced by a molybdenum target.
False: The filter is used to attenuate most of the continuous spectrum and leaves the characteristic radiation.The filter is relatively transparent to its own characteristic radiation.
Mammography:
General mammography uses a focal spot of 1 mm.
False: Focal spot is <0.3mm and for magnification 0.1mm.
Mammography:
The average dose per mammogram to glandular breast tissue is 2mGy.
True
- The intrinsic resolution in computed radiography (CR) is limited by:
A Pixel size.
B. Scattering of laser light in the phosphor layer.
C. Thickness of the phosphor layer.
D. Diameter of the scanning laser beam.
E. Orientation of the x-ray beam.
A Pixel size. True
B. Scattering of laser light in the phosphor layer. True
C. Thickness of the phosphor layer. True
D. Diameter of the scanning laser beam. True
E. Orientation of the x-ray beam. True
Compared to standard image plates (IPs), high resolution image plates (HRIPs) require a lower x-ray dose to produce an image.
False: A high resolution IP comprises a thinner layer of finer phosphor crystals and usually does not include a light reflection layer. HRIPs are reserved for examinations demanding high spatial resolution. High resolution imaging plates have lower fractional x-ray absorption efficiency and therefore demand a higher x-ray dose than standard lPs.
CR: A photostimulable phosphor plate is used as the image plate (IP).
True
CR: Absorption of an energetic x-ray photon gives electrons sufficient energy to jump from a conduction band into a valence band.
False: After the absorption of x-ray photons, electrons jump from the valence band into the conduction band.
CR: Electrons can decay into traps after promotion.
True
CR: High resolution image plates have high fractional x-ray absorption efficiency compared to standard IPs.
False: HRIPs have lower fractional x-ray absorption efficiency compared to standard lPs.
CR: Laser light can give trapped electrons enough energy to leave energy traps.
True: This is how the phosphor plate is read with a laser beam scanning to and fro across the plate.
CR: The stimulated emission signal in CR has a very low intensity.
True: The signal photons have to be collected with a photomultiplier.
CR: Photostimulable plates used in plain radiography are cheap and of single use.
False:The plates are expensive and can be reused.
CR: The dose latitude (dynamic range) of CR systems is in the order of 100:1. 1.DDOO: 1
False: the dynamic range of CR systems is in the order of 10^4:1 (10,000:1).
CR: Using CR system results in a lower rate of repeat exposures.
True: Due to the high dynamic range of CR systems, there is more consistent acquisition of images with lower occurrence of incorrectly (over or under) exposed images.
Regarding photostimulable phosphor plates (PSPs):
The commonly used storage phosphor comprises barium fluorohalide crystals activated with divalent europium ions.
True:The commonly used storage phosphor is BaFX:Eu2+. X stands for a specific mix of halogen atoms selected from bromine, iodine, and possibly chlorine atoms.
Regarding photostimulable phosphor plates (PSPs): A laser beam is passed across an exposed plate to read the image.
True
Regarding photostimulable phosphor plates (PSPs):
The image is read by continuous sampling.
False: The image from an IP is read by discrete sampling.
Regarding photostimulable phosphor plates (PSPs):
Plate reading can take place a long while after the image is taken.
False: Electrons will relax to their ground states from their metastable states as soon as a relaxation mechanism presents itself. If the IP is not read in good time, the image quality will degrade.
Regarding photostimulable phosphor plates (PSPs):
The density of the image depends on the exposure factors used.
False: The image density is independent of the exposure factors used.
Regarding photostimulable phosphor plates (PSPs):
A CR IP deteriorates over time due to laser desensitization.
False: The degradation of the IP is due to desensitization of the phosphor screen.
Regarding photostimulable phosphor plates (PSPs): The trapped electrons returning to their valence band release light photons of the same wavelength.
True
Regarding photostimulable phosphor plates (PSPs):
The modulation transfer function (MTF) is measured in line pairs per millimeter.
False: MTF is measured in line pairs cm-1.
Regarding photostimulable phosphor plates (PSPs):
The x-ray absorption efficiency of PSP is much higher compared to that of film screen systems.
False: The x-ray absorption efficiency of PSP is usually lower than film screen systems.
Regarding photostimulable phosphor plates (PSPs):
PSPs rarely produce image artefacts.
False: PSPs become worn or scratched with use and have to be replaced.
Regarding photostimulable phosphor plates (PSPs):
The latent image stored on a plate can decay if not read promptly.
True
Regarding photostimulable phosphor plates (PSPs):
The speed at which the plate is read depends on developer concentration.
FALSE. Developers are not used for image production in computed or digital radiography.
Regarding photostimulable phosphor plates (PSPs):
Resolution is affected by the thickness of the photostimulable phosphor layer.
True: A thicker phosphor layer causes more scatter, therefore reducing resolution.
Regarding photostimulable phosphor plates (PSPs):
The relative exposure versus output signal plot is a straight line.
True: Image parameters such as windowing can be altered during post processing
Calcium tungstate is regularly used as storage phosphor in the PSP plates used in digital radiography.
False: Calcium tungstate was used in film screen radiography in the past.
Spatial resolution of a standard CR system is significantly higher than that of competing film screen combination
False: Significantly lower.
Spatial resolution of a standard CR system depends on:
B. Diameter of the scanning laser beam.
C. Mean size of phosphor crystals.
D. Sampling interval (pixel spacing).
E. Spread of light as the laser beam penetrates the IP during readout.
B. Diameter of the scanning laser beam. True
C. Mean size of phosphor crystals. True
D. Sampling interval (pixel spacing). True
E. Spread of light as the laser beam penetrates the IP during readout. True
Wuantum mottle in computed radiography:
It is directly proportional to the square of photon fluence incident upon the image plate (N).
False. It is inversely proportional to the square root of photon fluence incident upon the image plate (N).
Quantum mottle in computed radiography:
It is directly proportional to the square of the fractional x-ray absorption efficiency (TJ).
False. It is inversely proportional to the square root of the fractional x-ray absorption efficiency (TJ).
Quantum mottle in computed radiography:
It is inversely proportional to the square root of photon fluence incident upon the image plate (N).
TRUE
Quantum mottle in computed radiography:
It is inversely proportional to the square root of the fractional x-ray absorption efficiency (TJ).
TRUE
Regarding digital radiography:
The charge coupled device converts photons into an electronic signal.
TRUE
Quantum mottle in computed radiography:
It refers to the noise that arises from the random fluctuation in the count of_x ray quanta absorbed in the image plate to form the primary image.
TRUE.
Regarding digital radiography:
The input phosphor is coupled to the charge coupled device by fibre optics
True: The input phosphor is coupled to the charge coupled device (CCD) by fibre optics to increase efficiency.
Regarding digital radiography:
Both flat panel array detectors and charge coupled devices have dead areas.
True.
Regarding digital radiography:
Resolution on a flat panel array is limited to the width of the detector elements.
True
Regarding digital radiography:
Image windowing can be altered after the image has been taken.
True
- The following are true of analogue images:
A. The image is made up of numerous screen pixels.
B. Can easily be stored directly on a computer:
C. Can be recorded onto a magnetic tape.
D. It is used in CT.
E. Analogue images can be displayed on monitors.
Re: Analogue images:
A. The image is made up of numerous screen pixels. False
B. Can easily be stored directly on a computer. False.
C. Can be recorded onto a magnetic tape. True
D. It is used in CT. False.
E. Analogue images can be displayed on monitors. True
The following are true of digital images:
A. The digital image is made up of pixels.
B. Each pixel is given a number which gives its greyscale level.
C. Each pixel is given a number which gives its point on the screen.
Re digital images:
A. The digital image is made up of pixels. True
B. Each pixel is given a number which gives its greyscale level. True
C. Each pixel is given a number which gives its point on the screen. True
The following are true of digital images:
The digital image can be directly displayed on a monitor:
False: It needs to be converted by a digital-analogue converter.
The following are true of digital images:
Conventionally in image display, pixels with lower values are displayed darker than ones with higher values.
False: Conventionally, higher value pixels are displayed darker than lower value pixels.
ALWAYS START WITH WHITE
Histogram analysis of a digital image involves plotting the frequency of pixels against pixel values.
True
Histogram equalization is done to adjust for contrast differences in the digital image.
True
Smoothing or blurring of features in the processed image is done by high pass filtering.
False. LOW PASS filters high frequencies leading to the smoothing or blurring of features.
Vignetting is done to improve diagnostic accuracy.
False: Vignetting is the phenomenon of losing light photons at the edge of an image. It is not used as a post-processing tool.
Low pass filtering causes enhancement of edges in the image.
False. HIGH PASS allows edge enhacement.
- Digital image acquisition and processing can be used by the following modalities:
A. Single photon emission computed tomography.
B. Magnetic resonance imaging.
C. Computed tomography.
D. Mammography.
E. Positron emission tomography.
ALL TRUE
In DSA: Enhanced vascular structures are seen together with bony and soft tissue structures.
False: In DSA, bones and soft tissue can be digitally subtracted.
In DSA: The subtraction is done using a mask image.
True
DSA does not require IV contrast administration.
False
The mA used for the DSA is the same as that used for normal screening.
False: The mA used is higher compared to normal screening to reduce noise.
In DSA: The main advantage of frame integration is the shorter exposure time.
False: Frame integration is a technique that was used in the past to decrease signal to noise ratio.This usually led to longer exposure times.
Images can be transmitted from plate to screen without processing.
FALSE
Digital tomosynthesis is used to obtain images at varying depths.
True: Digital tomosynthesis is the digital equivalent of tomography.
Quantum mottle is produced by high mAs.
Quantum mottle is produced by insufficient light photons or low mAs.
Heat blur is caused by the DR receptor being exposed to intense heat
True
Histogram error artefact is caused by the use of incorrect post-processing histogram.
True
- Regarding artefacts in digital subtraction angiography:
A Misregistration occurs due to structures in the mask image and contrast image not being in the same place.
B. Misregistration can be caused by peristalsis.
C. Misregistration can be resolved by moving the mask image.
D. Misregistration can be caused by the patient’s breathing.
E. Misregistration can be caused by cardiac motion.
ALL TRUE.
Thin film transistor (TFT) display screens are not suitable for use in diagnostic radiology.
False: TFT monitors are widely used.
TFT monitors are a subtype of cathode ray tubes (CRT).
False:TFT monitors are a subtype of LCD (liquid crystal display) screens.
TFT screens fare much worse compared to CRTs in detecting low contrast details.
False: In almost all studies,TFT screens were found to be as good as or better than CRT monitors.
TFT screens use less power and a smaller foot print compared to most CRTs.
True
Regarding solid state digital radiography (DR) detectors:
Each pixel area contains readout microcircuitry to make it possible to directly read the image out of the detector in electronic form.
True
Regarding solid state digital radiography (DR) detectors:
Fill factor (FF) of the detector is the sensitive area of the pixel / occluded area of the
pixel.
False: The fill factor (FF) of the detector is the sensitive area of the pixel / overall area of the pixel (where the overall area of the pixel = sensitive area + occluded area).
Regarding solid state digital radiography (DR) detectors:
The efficiency of signal recording is increased with increasing fill factor
True
Regarding DR detectors:
Amorphous silicon doped with hydrogen (a-Si:H) is more sensitive to radiation damage than crystalline Si.
False: a-Si:H is more tolerant to radiation damage unlike crystalline Si.
The greyscale resolution of a digital image is defined by the number of bits of information per pixel.
True
In general, the fill factor falls as the pixel sampling interval is increased.
False: FF falls as the pixel sampling interval is reduced.
The readout microcircuitry records light or electrical charge carriers and produces an analogue signal output.
True:The analogue signal is then digitized.
Indirect conversion detectors have higher image noise for the same patient dose compared to direct conversion detectors.
False:There is lower image noise for the same patient dose with indirect conversion detectors.
Regarding DR detectors:
The active matrix array (readout electronics) is manufactured from an amorphous form of silicon doped with hydrogen (a-Si:H).
True
The term 8 bits corresponds to a choice of 256 greyscale values
True. 2^8 = 256
Regarding DR detectors:
Most indirect conversion detectors use Csl:Tl (Caesium iodide:Thallium) as the scintillating layer.
True
Regarding DR detectors:
The typical thickness of the scintillating layer is about 10 mm
False:About 500 micrometres.
Regarding DR detectors:
In the read out process, the stimulating light and the output light need to be of the same wavelength.
False:The stimulating light and output light should be of different wavelengths (the former about 10^8 times larger).
The fractional x-ray absorption of direct conversion detectors is better than that of indirect conversion detectors.
False: Indirect is better than direct.
Indirect conversion DR detectors offer lower patient dose for the same image quality compared to direct conversion detectors.
True
The modulation transfer function (MTF) of indirect conversion detectors is better than that of direct conversion detectors
FALSE. Direct has a better MTF.
The spatial resolution of direct conversion detectors is better than that of indirect conversion detectors.
True
DR Detectors: Defective pixels in the active matrix array cause bright or dark spots in the image.
True
DR Detectors: Non-uniform variations in sensitivity of the x-ray absorption layer causes irregular shading across the image field.
True
DR Detectors: Irregular shading can be corrected by pixel correction.
False. Irregular shading can be corrected by GRAIN correction.
DR Detectors: DDefects in the pixel array can be corrected by gain correctio
FALSE. Defects in the pixel array can be corrected by PIXEL CORRECTION.
DR Detectors: Artefacts are removed at the time of image acquisition
False: Artefacts are removed at the time of post-processing.
Modification of the image greyscale using a look-up-table (LUT) might be done for the following reasons:
A. To vary the mean brightness of an image.
B. To compensate for the different intensity responses of display devices.
ALL TRUE
Modification of the image greyscale using a look-up-table (LUT) might be done for the following reasons:
A. To increase the spatial resolution of small isolated structures.
B. To improve the sharpness of edges.
C. To improve the presentation of fine texture patterns.
ALL FALSE
Spatial feature enhancement of images using an unsharp mask algorithm might be done for the following reasons:
A To increase the visibility of small isolated structures.
B. To improve the sharpness of edges.
C. To improve presentation of fine texture patterns.
ALL TRUE
Spatial feature enhancement of images using an unsharp mask algorithm might be done for the following reasons:
A. To increase image contrast to improve the visibility of a subtle lesion.
b. To improve the presentation of the overall greyscale range.
FALSE. USE A LOOK UP TABLE (LUT)
Regarding DR detectors:
In indirect conversion detectors, the latent image is read out one line at a time.
True
Regarding DR detectors:
In direct conversion (DR) detectors, Hgl2 is used as the x-ray scintillator:
False: Direct conversion detectors do not use scintillators.
Regarding DR detectors:
The most common photoconductor used in direct conversion detectors is amorphous Selenium (a-Se).
True
Regarding DR detectors:
In direct conversion DR detectors, a metal electrode is coated on the external surface of the amorphous selenium.
True.
Regarding DR detectors:
The metal electrode is attached to a positive bias potential of 220V
False: 5000 Volts.
In AMFP (active matrix flat panel) displays, the image is generated by scanning the phosphor screen with a focused beam of electrons.
False: This is how the image is produced in CRT displays.
A CRT display uses two sheets of polarizing material.
False:This is a feature of AMFP displays.
CRT monitor images are susceptible to a degradation in quality due to geometrical distortion.
True.
AMFP monitor images are susceptible to contrast loss
False: CRT monitors are susceptible to contrast loss.
Displays: The polarizing properties of liquid crystal can be rotated in response to the magnitude of an applied electrical voltage
True
DR: It is easy to asses whether the patient has been over- or underexposed by just looking at the display.
False: DR detectors have a wide latitude and post-processing ensures that the displayed image is optimized in terms of its greyscale presentation.
DR: Detector dose indicators (DDIs) are special electronic devices incorporated into the detectors to measure patient dose.
False: DDI is determined from the signal from the plate averaged over a broad region of the plate.
DR: DDIs are analogous to the optical density of films.
True
DR: Hight or low detector dose indicators indicate over or under exposure
FALSE FOR BOTH. The definition of DDI is manufacturer dependent.
DICOM definitions:
Modality worklist permits the retrieval of scheduling information for that modality and patient demographics from the radiology information system.
True.
DICOM definitions:
Modality push allows the system to store images to PACS
TRUE.
DICOM definitions:
Modality push allows the modality to query PACS and to find out about previous images for the patient.
False: Modality push allows the system to store images to PACS.
DICOM definitions:
Modality pull allows the system to store images to PACS.
False: Modality pull allows the modality to query PACS to find out about previous images for the patient.
DICOM definitions:
Print service allows the modality to print to a network printer.
True.
DICOM definitions:
The modality performed procedure step provides information on whether the examination in the worklist is in progress or completed.
True.
Re: Imaging terminology
The modulation transfer function is the ratio of input modulation to output modulation.
False. Output: Input
Re: Imaging terminology
The Nyquist criterion states that the sampling frequency must be at least twice the highest frequency present in the signal.
True.
Re: Imaging terminology
Nyquist frequency is equal to two times the sampling frequency
False: Nyquist frequency is equal to half the sampling frequency.
Re: Imaging terminology
Aliasing will occur if the signal frequency is less than the Nyquist frequency.
False: Aliasing will occur if the signal frequency is more than the Nyquist frequency.
Re: Imaging terminology
Nyquist frequency is the maximum signal frequency that can be accurately sampled
True
In DSA: To achieve high resolution, large focal spot sizes are necessary.
False: As in conventional radiography, to achieve high resolution small focal spot sizes are necessary.
In DSA: In modern DSA systems, it is not necessary to use the same frame as mask for each subtraction.
True.
In DSA: X-ray tubes with lower rating can be used in DSA.
False: The x-ray tubes used will have to be of a higher rating due to the necessity to produce multiple images rapidly.
In DSA: Subtracted images have very high signal to noise ratio compared to non-subtracted images.
False: Subtracted images usually have a low signal to noise ratio compared to non subtracted images.
A Digital mammography system offers a wider dynamic range compared to a film screen system.
True.
The spatial resolution with direct capture method is limited by the PIXEL SIZE and not to the thickness of the photoconductor.
TRUE.
Digital mammography offers better spatial resolution than conventional film screen mammography.
False. The maximum resolution achievable with a digital detector is 5-9 line pairs per millimetre which is significantly lower than that of film-screen mammography
The breast dose using a digital mammography system is higher than for the film screen mammography system
False. It is lower, mainly due to the inherently higher detection efficiency of digital detectors and the use of a harder x-ray beam at each breast thickness.
Digital mammography is better than film mammography in screening women who are under the age 50.
True.
Fluoroscopy Image Intensifier:
Glass envelope contains inert argon gas.
False. Vaccum
Fluoroscopy Image Intensifier:
The metal housing is designed to prevent stray light getting into the tube and to shield from magnetic fields.
True.
Fluoroscopy Image Intensifier:
The main components within the tube are the input screen, focusing electrodes and output screen.
True.
Fluoroscopy Image Intensifier:
The focusing electrodes are designed to channel photons from the input screen directly towards the output screen.
False: They focus the electron beam from the input screen onto the output screen.
Fluoroscopy Image Intensifier:
The input screen is much larger than the output screen.
True. Hence the MINIFICATION GAIN.
Input screen of an image intensifier must be perfectly flat for an undistorted image.
False. Its CURVED.
IIs: The outer layer is the input phosphor and is usually caesium iodide.
True.
IIs: The inner side of the screen is the photocathode, which emits electrons when the x-ray beam hits it.
False: Photocathode emits electrons when light from the input phosphor hits it.
IIs: The input phosphor is one large flat crystal.
False: It is a 0.1-0.4mm thick layer of needle-like Csl crystals arranged perpendicular to the screen to allow for internal light reflection.
IIs: The input phosphor can pick up approximately 60% of the incoming x-ray photons.
True.
The II output screen:
Is usually 25-35mm in diameter.
True.
The II output screen:
Is a pure layer of silver-activated zinc-cadmium-sulphide.
False: To stop backscatter of light and act as the anode, a very thin layer of aluminium covers the screen.
The II output screen:
Converts the electron beam into light.
True: Green light is produced.
The II output screen:
Has an anode with a positive potential of approximately 25k\/.
True
The II output screen:
E. Emits light bright enough to be seen with the naked eye.
True
In an II, Electrons from the photocathode are accelerated towards the output screen via a series of dynodes.
False: Dynodes are used in photomultiplier tubes. In the image intensifier focusing electrodes ensure the spatial image is preserved from input to output screen.
In an II, Approximately 100 000 light photons are emitted from the output screen for every x-ray photon detected.
True.
In an II, COutput is usually viewed directly by a TV camera.
True:A TV system results in minimal loss of information and the signal can be recorded to keep a record of the procedure.
In an II, Reduced x-ray intensity at the centre of the screen causes increased brightness at the periphery of the image.
False: X-ray intensity is reduced at the periphery of the curved screen, so the periphery of the image is less bright (vignetting).
In an II, conversion factor is the ratio of luminescence of the output phosphor to the input - exposure rate.
True
The electron beam in an image intensifier:
Is accelerated from input to output screen.
Can be distorted by external electromagnetic fields
Is re-focused when a magnified field of view is selected.
All true
The electron beam in an image intensifier:
Contributes to brightness gain only through minification of the image.
False: It contributes through minification gain and also amplification (flux) gain (through the increase in energy due to acceleration).
Brightness gain in an image intensifier:
Ratio of output phosphor brightness to input phosphor brightness.
True
Brightness gain in an image intensifier:
Is only through minification of the image.
False: It is through electron acceleration (flux gain) and minification gain.
Brightness gain in an image intensifier is approximately 50 x
False: It is more like 5000 (product of flux gain and minification gain).
Brightness gain in an image intensifier:
Increases with increased voltage across the intensifier.
True:This increases electron acceleration, therefore increases flux gain and increases overall brightness gain.
Brightness gain in an image intensifier: Increases if the output phosphor size is increased.
False: Increasing the output phosphor size reduces the minification gain and therefore reduces overall brightness gain.
Image magnification in fluoroscopy:
Requires a change in the distance between input and output screens.
False: This distance is fixed.The voltage of the focusing electrodes.
Is changed to move the electron beam crossover point nearer to the input screen, so the central part if the input image fills the whole of the output phosphor.
Image magnification in fluoroscopy:
Results in better resolution of the image than with the full field of view.
True, image magnification in fluoroscopy generally results in a better resolution of the image compared to using the full field of view, as it essentially zooms in on a smaller area, providing more detail within that region, although this often comes at the cost of increased radiation dose to the patient due to the need for higher exposure settings to maintain image quality
Image magnification in fluoroscopy:
Does not require an alteration in exposure factors to maintain similar brightness of image compared to the full field of view.
False: The magnified view has reduced minification gain, therefore reduced brightness.To restore the brightness, exposure factors must be increased.
Image magnification in fluoroscopy:
Results in increased patient skin dose.
True: Dose increases in order to maintain image brightness.
Image magnification in fluoroscopy:
Is usually achieved by reducing the object to intensifier distance.
False: Although this will produce magnification, it is the re-focusing of the electron beam that produces the magnified image.
Quantum noise in the image produced by an image intensifier: Is mostly due to thickness variation of the input phosphor.
False: This causes screen structure noise.
Quantum noise is the predominant cause of overall noise in the II system.
True.
Quantum noise in the image produced by an image intensifier: Can be reduced by increasing the exposure rate.
True: Increased dose to the input phosphor means that the signal-to-noise ratio is increased.
Quantum noise in the image produced by an image intensifier:
Is increased if the input screen is thicker.
False. More photons are detected.
Quantum noise in the image produced by an image intensifier: Is more likely to compromise the quality of low-contrast images compared to high contrast images.
True.
In fluoroscopy, the TV camera:
Converts visual information from the output screen of the image intensifier into electronic form.
True.
In fluoroscopy, the TV camera:
Contains an electron beam from the cathode that is focused and directed by coils so that it scans the signal plate.
True, that’s how an overall works!
In fluoroscopy, the TV camera: Contains a mesh anode that overlies the graphite signal plate.
True. Contains a mesh anode that overlies the graphite signal plate, which in turn overlies the insulated layer containing small globules of photoconductive material.
In fluoroscopy, the TV camera:
Produces a voltage at the signal plate that is proportional to the intensity of light being scanned.
True
In fluoroscopy, the TV camera:
Has a resolution that is better than the resolution of the image intensifier.
False: The image intensifier can resolve 4:–5 Ip mm-1 but the TV camera has a fixed number of scan lines and will never have better resolution than the intensifier: On the TV screen the resolution may be as low as 1.2 Ip mm-1.
Fluoroscopy:
Uses digital processing, including noise-reduction or edge-enhancement, by a computer prior to display.
True
Fluoroscopy:
Uses an automatic system to drive the film cassette into place ready for spot image acquisition.
False: That was the case for older analogue image intensifiers-modern ones take digital spot images at higher mA than for fluoroscopy, but using the same camera equipment.
Fluoroscopy: Utilize fibre-optic connections between the output face of the intensifier and the
camera input.
True: Traditional lens systems are now being replaced by fibre-optics for improved light collection and improved geometrical integrity.
Fluoroscopy: With charge coupled device (CCD) cameras that use amorphous silicon pixels to convert the incoming light into a digital signal, has rapid read-out of approximately 30 frames per second.
True: It is more efficient converting the light directly into a digital signal.
Fluoroscopy: Eliminates the distortion across the field that is present in fluoroscopy images.
False: A test object will appear curved at the edges of the image.The curvature of the input screen attempts to minimize this. However it cannot completely be eliminated even with modern image processing.
Fluoroscopy:
The focus to skin distance should not be less than 45cm.
True: For non-mobile equipment it should not be less than 30cm and ideally greater than 45cm.
Fluoroscopy: Using the smallest field size results in improved spatial resolution.
True: The smaller field size is a magnified view and so has better resolution.
Fluoroscopy:
The quantum sink in the formation of the image is the output phosphor.
False: Overall image quality is determined at the point in the image formation process where the number of photons that contribute to the image is THE LEAST.
This is the quantum sink and it is the INPUT PHOSPHOR for an II!
Fluoroscopy: The tube is operated at a much lower tube current than in conventional radiography.
True: 25kV as opposed to around 80k\/.
Think about how long it is running for!
Fluoroscopy: The maximum tube current is limited by the focal spot size.
False: It is limited by patient dose restrictions
Fluoroscopy: Automatic brightness control:
Allows adjustments to be made in the brightness of the image solely by adjustment of the mA.
False: mA and/or kV may be adjusted to optimize image brightness.
Fluoroscopy: Automatic brightness control:
Utilizes the brightness of the central portion of the image in order to optimize the image brightness.
True: In general the user will have centred the region of interest in the centre of the screen.
Fluoroscopy: Automatic brightness control:
Takes as an input signal a measurement of the light intensity of the image intensifier
output screen.
True.
Fluoroscopy: Automatic brightness control:
May lead to poor image quality if the x-ray field extends beyond the patient.
The unattenuated part of the beam or result in a very bright portion of the image, leading to a darker image when the brightness is automatically adjusted
Fluoroscopy: Automatic brightness control:
May produce an image with less quantum noise if the mAs are higher.
True: Although the dose will be higher to the patient.
Vignetting in fluoroscopy: Is more marked with less curved input phosphor screens.
True:The greater curve of the input screen helps to focus the electron beam.
Vignetting in fluoroscopy: Causes the image to be brighter centrally.
True
Vignetting in fluoroscopy: Can be improved by strict quality control.
True
Vignetting in fluoroscopy: Is due to electron loss from the periphery of the electron beam.
True
Vignetting in fluoroscopy:
Is caused by non-uniform magnification across the intensifier tube.
True: There is more magnification at the periphery of the image.
Fluoroscopy dose rate at the input phosphor is
1 micro Gy s-1
TRUE.
Fluoroscopy: Maximum entrance surface dose should not exceed 100 mGy min-1
TRUE.
Fluoroscopy: Skin dose may be up to 10 times higher than the dose at the input phosphor.
False: It can be 300 times higher:
Fluoroscopy: A spot image taken during fluoroscopy has a dose of 10 micro Gy per frame.
False: 1 micro Gy per frame.
Fluoroscopy: The Health and Safety Executive must be informed if the patient dose is five times the intended dose.
True: The HSE must be informed if the dose is between 10 times that intended.
Subtraction techniques in fluoroscopy:
No need to take a mask image if energy subtraction is used.
True:The rapid switching between a low and high kV avoids the need for a mask image.
Subtraction techniques in fluoroscopy:
There can be significant movement blur in the images produced by dual energy subtraction.
False: The high- and low-kV images are produced simultaneously.
Subtraction techniques in fluoroscopy:
In digital subtraction angiography very high doses of contrast medium are required for adequate visualization of vessels adjacent to bony structures
False: Lower doses can be used, as there is good vessel clarity once the bones and overlying soft tissues have been digitally subtracted.
Subtraction techniques in fluoroscopy:
Exposure factors must be kept constant for the mask and the contrast images in digital subtraction imaging.
True.
Subtraction techniques in fluoroscopy:
Time interval differencing can be used in cardiac imaging to produce subtracted images
timed to the cardiac cycle.
True: Images are produced as the difference between images separated by a fixed interval of time, rather than all from the same mask image.
In DSA: An image without contrast medium is electronically added to an image with contrast.
False:The image without contrast is subtracted from the image with contrast
In DSA: The mask image is taken prior to administration of contrast.
True.
In DSA: The signal-to-noise ratio is increased following subtraction.
False: Signal-to-noise ratio is reduced following subtraction.
In DSA: Post-processing using pixel shift can help eliminate motion artefact.
True.
In DSA: Frame integration is a form of post-processing where several frames are summed to form the final image.
True: Retrospective summation of several frames improves the signal-to-noise ratio in the final image.
Regarding quality control in fluoroscopy:
Automatic brightness control is tested with the grid.
False: The grid checks for image distortion. Brightness of the light output from the intensifier and TV monitor are assessed, but as deterioration in performance in the system can be masked by automatic brightness control, x-ray output must be measured.
Regarding quality control in fluoroscopy:
Limiting resolution can be measured with a line pair phantom.
True
Regarding quality control in fluoroscopy:
Contrast resolution can be tested with a Leeds test object containing varying sizes and contrasts of high atomic number material
True
Regarding quality control in fluoroscopy:
A lag of 1ms is typical for modern image intensifiers.
True
Regarding quality control in fluoroscopy:
Vignetting should be less than 25%.
True
Digital flat plate detectors in fluoroscopy:
Utilize amorphous silicon detectors with caesium iodide scintillators.
True.
Digital flat plate detectors in fluoroscopy:
Have equivalent detective quantum efficiency to image intensifiers
True: About 65%.
Digital flat plate detectors in fluoroscopy:
Display more limited image contrast than an image intensifier can through a TV system.
False: Contrast resolution is limited through a TV system, but via a digital detector is much greater and makes use of the 14-bit depth that is typically available.
Digital flat plate detectors in fluoroscopy:
Display good spatial resolution of up to 20 Ip mm-1.
FALSE.
Resolution is better than standard image intensifiers,
but with a pixel size of about 150µm, it will be about 3 Ip mm-1.
Digital flat plate detectors in fluoroscopy:
Provide undistorted displayed images compared to standard image intensifier images.
True: As the detector is flat
Digital flat plate detectors in fluoroscopy:
Dynamic range is better than with conventional image intensifiers.
True
Digital flat plate detectors in fluoroscopy:
The image produced is rectangular in shape.
True:The image displayed is the same shape as the detector.
Digital flat plate detectors in fluoroscopy:
Image noise is reduced by using a smaller field of view.
False: Image noise is unaffected by a change in the field size.
Digital flat plate detectors in fluoroscopy:
X-rays are directly converted to an electrical signal without the need for light production.
False: Light is produced by the caesium iodide scintillator and then detected by the amorphous silicon detectors.
Patient doses in fluoroscopy can be reduced by:
Careful collimation around the region of interest.
Low pulse rate digital fluoroscopy.
Digital image acquisition rather than conventional film.
All true
Patient doses in fluoroscopy can be reduced by:
Using magnified views.
False:Although the volume of patient irradiated is smaller, exposure factors are increased to compensate for the smaller minification of the magnified field of view.
Patient doses in fluoroscopy can be reduced by: Using an over couch x-ray tube.
FALSE. DOSE IS HIGHER WITH OVERCOUCH due to BACKSCATTER
The radiation exposure rate is lower for fluoroscopy than for radiography.
True: For example, fluoroscopy of a typical adult abdomen requires 45mGy/min. For an abdominal radiograph, entrance skin exposure is approximately 3mGy with an exposure time of 200ms and an exposure rate of 900mGy/min.
The total exposure dose for a radiograph is lower than fluoroscopy.
True: This is because in fluoroscopy despite having a lower exposure rate, the total exposure time is extended for the whole examination.
Over-table tube configurations result in increased radiation exposure for the operator than under-table tube systems.
True: As the scattered radiation from the patient is more concentrated in the direction towards the x-ray tube.
The biplane fluoroscopic system uses a single image intensifier to create 2 separate images.
False: Biplane systems use two separate imaging chains so that it is possible to record two projections (e.g. frontal and lateral) simultaneously.
Filtration is not used in fluoroscopy.
False: Filtration is added to attenuate low-energy x-rays from the beam. Aluminium is most commonly used.
Regarding collimation in fluoroscopy: It increases the exposed tissue volume.
False. Opposite.
Regarding collimation in fluoroscopy: Collimation is usually made automatically so that it is no larger than the field of view (FOY).
True: Although, it is often useful for the operator to further collimate the beam to the area of clinical interest.
Regarding collimation in fluoroscopy: It reduces scatter production.
True.
Regarding collimation in fluoroscopy: It reduces image contrast.
False: It improves image contrast by reducing scatter.
Regarding collimation in fluoroscopy: It reduces glare from unattenuated radiation near the edge of the patient’s body.
True.
Regarding equalization filters: They are totally radio-opaque.
Equalization filters are partially radiolucent blades that are used to provide further beam shaping in addition to collimation.
Regarding equalization filters: They are the same as collimators.
False. Equalization filters are partially radiolucent blades that are used to provide further beam shaping in addition to collimation.
Regarding equalization filters: They are also known as wedge filters.
True:They are also known as contour filters.
Regarding equalization filters: They reduce glare from unattenuated radiation near the edge of the patient.
True.
Regarding equalization filters: They are made of lead-rubber or lead-acrylic sheets.
True.
An image intensifier converts incident x-rays into a minified image.
True.
An image intensifier amplifies image brightness for better visibility.
True.
IIs: The input layer converts electrons into a visible image.
False:That is the function of an output layer: Input layer converts x-rays into electrons.
IIs: Electron lenses work to accelerate electrons.
False: Electron lenses are used to focus electrons.
All components of the image intensifier are contained within a vacuum.
True.
Intermittent fluoroscopy is a dose reduction method in fluoroscopy
True
Removal of grid is a dose reduction method in fluoroscopy
True: The use of a grid increases the dose, but it is used primarily to increase contrast and image quality.
Last image hold is a dose reduction method in fluoroscopy
True:The last image is ‘digitally frozen’ so that the operator can look more closely at the last image without having to continually expose the patient.
Image magnification reduces dose in fluoroscopy
FALSE. INCREASES DOSE
Dose spreading is a dose reduction method in fluoroscopy
True: A reduction of the maximum skin dose can be achieved by rotating the fluoroscope but remaining centred on the area of interest and therefore the maximum dose is spread over a broader area of patient’s skin.
Regarding the image intensifier: It intercepts the x-ray photons and converts them into visible light photons.
True
Regarding the image intensifier: The visible light photons converted from x-ray photons are amplified.
True
Regarding the image intensifier: It creates a large intensification in luminance at the output screen compared with that at the input screen.
True
Regarding the image intensifier: The image intensifier is located opposite the x-ray tube.
True
Regarding the image intensifier: The larger the image intensifier; the higher the cost.
True
The following are artefacts in fluoroscopy: Lag
True: This is a persistence of luminescence after x-ray has been stopped.
The following are artefacts in fluoroscopy: Vignetting
True: This results from an unequal collection of light at the centre compared to the periphery.
The following are artefacts in fluoroscopy: Veiling glare
True:This is from scattering light and a defocusing of photoelectrons
The following are artefacts in fluoroscopy: Pincushion distortion.
True: This is a geometric, non-linear magnification across the image that results from a magnification difference at the periphery of the image.
The following are artefacts in fluoroscopy: S Distorsion
True: External electromagnetic sources affect electron paths at the periphery of the image intensifier more than at the centre and can cause the image distortion in an S-shape.
Fluoroscopy: For still images, the best resolution can be achieved using a film screen combination with a spot film device.
True
Fluoroscopy: Photospot cameras allow more rapid multiple-exposure sequences at a lower radiation dose than spot film.
True
Fluoroscopy: A photospot camera obtains a smaller image size than a spot film device.
True
For recording motion, cine fluorography gives the highest resolution images.
True
For recording motion, cine fluorography gives the highest dose rates.
True: Cine fluorography gives the highest resolution but also the highest dose rates compared with videotape recording of high-resolution TV.
DSA: The subtraction process reduces image noise.
False: Subtraction process increases image noise, but the perception of low-contrast vessels is increased due to the removal of distracting background tissue
DSA: With proper calibration, quantitative data can be measured.
True: It is common practice to measure the degree of stenosis, for example.
DSA: A road map cannot be used in conjunction with live fluoroscopic images.
False: The idea of road mapping is to provide an overlay of a static image (such as that of the vasculature) over the real-time images. In addition, ‘image fade’ allows the operator to manually adjust the brightness of the static vessel road map overlay.
DSA: To image the entire peripheral vasculature using the stepping table technique, the imaging gantry is fixed while the patient table moves the area of interest into the field of view.
True
DSA: E. To image the entire peripheral vasculature using the stepping gantry technique, the patient table is fixed while the imaging gantry moves the field of view over the area of interest.
True
DSA: Mask pixel shift is a technique used to re-register pre- and post-contrast images.
True: This may help if the patient has moved between pre- and post-contrast images.
DSA: Image summation is useful when the frame rates are too slow during contrast injection.
False: Imaging frames may occur so rapidly that only part of contrast filled vessel is captured. Summation is used so that a complete vessel segment filled with contrast is obtained within a single image.
DSA: Temporal frame averaging is used to decreased displayed image noise.
True: This is done by creating an average between the current and one or more previous frames.
DSA: Adjustment of window widths and levels is not possible.
False: This can be done and is termed grey-scale processing.
Fluoroscopy: Pulsed mode fluoroscopy offers much better spatio-temporal resolution than continuous mode fluoroscopy.
True: This is particularly evident when imaging rapidly moving anatomy, such as coronary vessels in cardiac angiography or structures within the young infant.
Fluoroscopy: In the UK, the maximum entrance skin dose rate limit for a standard patient is 100mGy per minute.
True: Although in practice, a lower maximum dose rate limit of 50mGy per minute is more commonly adopted.
Fluoroscopy: Automatic Brightness Control (ABC) is the same as Automatic Exposure Control (AEC).
False: AEC is used in radiography.
Fluoroscopy: The purpose of ABC is to maintain stable viewing conditions independent of patient size, body sections, and projection angle.
True
Fluoroscopy: The operator should not manually adjust collimation as this is done automatically.
False: Manually adjusting collimation on to the clinical region of interest is good practice to reduce dose.
Staff dose in the fluoroscopy suite:
Leakage from x-rays from tube housing is typically 5 µGy/hr at 1m distance.
True. Limit is 1 mGy/hr at 1m
Staff dose in the fluoroscopy suite:
X-rays scatter from the patient accounts for most of stray radiation.
True.
Staff dose in the fluoroscopy suite:
Secondary scatter from structures in the room accounts for most of stray radiation.
False. X-rays scatter from the patient accounts for most of stray radiation.
Staff dose in the fluoroscopy suite: X-ray scatter intensity is greater on the beam exit side of the patient.
False: It is much greater on the beam entrance side of the patient. (BACKSCATTER)
Staff dose in the fluoroscopy suite:
At 1m from the patient, the scatter is typically about 1% of the patient entrance dose rate.
False: It is typically about 0.1% of patient entrance dose rate at 1m.
Fluoroscopy: Automatic Brightness Control (ABC) keeps the IMAGE INTENSIFIER entrance dose rate the same for patients of different sizes.
TRUE.
Fluoroscopy: ABC keeps the brightness of the output display constant independent of image intensifier entrance dose rate
True.
Fluoroscopy: The patient entrance dose rate is reduced by increasing the thickness of a copper beam spectral filter.
True.
The patient entrance dose rate is increased by reducing the fluoroscopy pulse rate from 30 to 15 frames per second.
False: Patient entrance dose rate is reduced by reducing the fluoroscopy pulse rate from 30 to 15 frames per second
Fluoroscopy: Selecting zoom view increases the patient entrance dose rate.
True
Regarding the image intensifier television (IITV) system:
It uses optical lenses to transfer images from II output screen to television sensor
True
Regarding the image intensifier television (IITV) system:
The primary lens is located adjacent to the TV camera sensor.
False: The primary lens is located adjacent to the II output screen.
Regarding the image intensifier television (IITV) system:
A circular iris is located between the primary lens and the TV lens.
True
Regarding the image intensifier television (IITV) system:
A circular iris aperture of adjustable diameter is normally used to calibrate the light intensity illuminating the image recording device.
True: The iris aperture is also used to compensate for some fall in II gain when a zoom field is selected.
- The following are examples ofTV sensors used in fluoroscopy:
A. Vidicon.
B. Plumbicon.
C. Chainicon.
D. Saticon.
E. CCD solid-state sensor
ALL TRUE
All are examples of various TV sensors and differ in terms of contrast, spatial resolution, lag, and target burn resistance. Solid-state charge coupled device (CCD) sensors are superseding the traditional electronic camera tube as the preferred image recording device in modern IITV fluoroscopy systems.
Regarding the image intensifier television (IITV) system:
An electronic light sensor can be mounted between the primary lens and TV lens to measure the brightness of the II image
True: This can give the real-time dose rate.
Regarding CCD sensors: They cannot be used for serial exposure applications.
False: They can be used for serial exposure applications.
Regarding CCD sensors: They are small and inexpensive.
True.
Regarding CCD sensors: They have negligible temporal unsharpness.
True.
Regarding CCD sensors: They have poor thermal, electrical, and magnetic stability.
False: They have excellent thermal, electrical, and magnetic stability.
Regarding CCD sensors: They have poorer geometrical precision when compared with traditional TV camera tubes.
False: They have good geometrical precision and spatial uniformity.
II: The degree of II amplification of an x-ray image is known as the brightness gain.
True.
II: Brightness gain is the ratio of the brightness of the output screen compared to that of the input screen.
True.
II: Brightness gain is the product of minification gain and flux gain.
True.
II: The conversion factor (Gx) is used as a measure of x-ray II tube sensitivity.
TRUE.
In measuring the ability of the II tube to amplify the signal we are unable to measure the brightness of the input screen, which limits the use of the Gbrightness. Instead we now use the image intensifier conversion factor (Gx).
Gx = L / X’
L = luminance of the II output (units = candelas m-2)
X’ = II entrance dose rate (units = μGy s-1
II: Minification gain is the increase in brightness due to geometrical magnification.
False: It is due to geometrical demagnification of the image.
II: Minification gain depends on the diameter of the input and output phosphors.
True. Minification gain = (Dinput / Doutput) ^ 2
II: The conversion factor (Gx) is inversely proportional to the luminance of output phosphor (L).
FALSE.
image intensifier conversion factor (Gx).
Gx = L / X’
L = luminance of the II output (units = candelas m-2)
X’ = II entrance dose rate (units = μGy s-1
SO DIRECTLY PROPORTIONAL
II: The conversion factor (Gx) is inversely proportional to the II entrance dose rate (X’).
TRUE.
image intensifier conversion factor (Gx).
Gx = L / X’
L = luminance of the II output (units = candelas m-2)
X’ = II entrance dose rate (units = μGy s-1)
II: The conversion factor (Gx) can be measured using a calibrated dose rate meter and a luminance meter.
TRUE.
The conversion factor (Gx) of a modern x-ray II tube typically lies in the range of
100-300 Cds µGy-1m-2.
False: This typically lies in the range of 10-30 Cds µGy-1 m-2
CT: Typical kVp value for the x-ray tube is about 80-140KV.
True: Typical kVp value is about 120.
CT: Transmitted x-ray intensity is measured by the detector.
True. It may be considered a low-dose examination in comparison to plain radiography.
CT: It may be considered a low-dose examination in comparison to plain radiography.
False: High dose examination. CT accounts for more than 40% of radiation from medical examinations.
CT: The main interaction in CT scanning is the Compton effect.
True
CT: The x-ray beam emerging from the tube housing in a CT scanner is significantly attenuated.
False: There is only a small loss of photon energy when the beam travels through the tube housing.
Regarding CT scanners: Most multi-slice scanners are based on fifth generation scanner geometry.
False: Most multi-slice scanners are based on third-generation scanner geometry.
Regarding CT scanners: An x-ray tube is mounted with its anode cathode axis perpendicular to the axis of rotation.
False:The anode cathode axis is parallel to the axis of rotation.
Regarding CT scanners: The axis of rotation is called the x-axis by convention.
False: The axis of rotation is called the Z-axis.
Regarding CT scanners: Bow-tie filters are used to even out a beam-hardening effect.
True
Regarding CT scanners: Fifth-generation scanners employ an electron source to produce an electron beam.
True
CT Gas detectors contain inert gases at pressures of about 1-2 atmospheres.
False: The inert gases are contained at about 25atm. to increase detector efficiency.
CT detectors should be manufactured with identical sensitivities.
False:The detector sensitivities are calibrated during imaging.
CT Pixel size is determined by the detectors
False: The computer system determines the pixel size
CT spatial resolution of the scanner is influenced by the detectors.
True: The smaller the individual detector, the higher the resolution.
Sodium iodide crystals are the commonest detectors used in modern scanners.
CT scanners use a variety of crystals in their detectors, including
Cadmium telluride (CdTe),
Cesium iodide (CsI),
Cadmium tungstate CdWO4
Bismuth germinate, and
Ceramic rare earth compound
Third-generation scanners are more efficient in eliminating scattered radiation than first- generation scanners.
False: Third-generation scanners produce more scatter compared to first-generation scanners.
Tube rotation enables tube loading to be lower compared to plain radiographs.
False: Tube loading is much higher compared to plain radiographs.
The irradiated slice thickness of the patient can be regulated by detector collimators.
TRUTH.
The fan beam is parallel to the anode cathode axis of the CT x-ray tube.
False:The fan beam is perpendicular to the anode cathode axis.
CT detectors may consist of crystals embedded in a matrix.
False: CT detectors consist of single large crystals. Intensifying screens consist of crystals embedded within a matrix.
The minimum detectable contrast of CT images is <0.5%.
TRUE
Solid state detectors are less efficient than gas filled ionization detectors.
False: Solid state detectors have higher efficiency than gas filled ionization chambers.
Using crystals with highly efficient absorption results in a crosstalk artefact.
False: Increasing the efficiency of absorption results in less crosstalk artefact.
Slice thickness can be increased by coupling together the signal from adjacent detectors.
True
The detectors need to be as small as possible.
True
Collimation of the CT scanner is fixed.
False. Collimation can be changed.
he most common image reconstruction technique used in modern CT scanners is filtered back projection.
True
Beam collimation happens before passing through the patient.
True
Multiple X-ray tubes are commonly used to acquire data in modern scanners.
False:A single x-ray tube is used.There are a few scanners that have more than one x-ray tube (currently for research only).
Solid state detectors are more efficient than gas filled detectors.
True
The afterglow of bismuth germinate detectors is higher compared to sodium iodide crystals.
False:The afterglow of bismuth germinate detectors is lower compared to sodium iodide crystals.
The typical thickness of the copper filters used is 0.5 mm.
True. Copper filters are normally 0.5 mm
The effect of scattered radiation is eliminated by using energy discriminators.
False: Discriminating windows are used in GAMMA CAMERAS.
In fourth-generation CT design, the detectors rotate.
False:The x-ray tube rotates and there is a ring of stationary or fixed detectors 4th Gen - Rotate/Stationary
In all modern scanners, each detector has its own collimator.
Only a few scanners in the market have this design feature.modern CT scanners
Modern CT scanners in use thousands of detector elements.
True
Modern CT scanners: Scattered radiation is controlled by detector collimation.
True
Modern CT scanners: The efficiency of sodium iodide crystals is about 50%.
FALSE.
The efficiency of Nal crystals approach 100%.
Modern CT scanners: The effective dose to the patient is measured for every CT scan.
FALSE.
‘Pixel’ stands for ‘x-ray picture’
False: Pixel stands for ‘picture element’.
Modern CT scanners: Ring artefacts are caused by the miscalibration of detectors in third-generation scanners.
True: Ring artefacts are caused by the miscalibration of one detector in a rotate-rotate geometry scanner. If a detector is miscalibrated, or faulty, it will record faulty information in every projection.This misinformation is reconstructed as a ring in the image with the radius of the ring determined by the position of the faulty detector within the detector array.
‘Voxel’ stands for ‘volume element’.
True.
The average linear attenuation coefficient of a voxel is represented as a pixel in the CT image.
True: Voxel is the volume element in the scan slice matrix and pixel is its representation in the image.
Star artefact in CT can be produced by simple back projection.
True.
A voxel is a three-dimensional region within a scan slice matrix in CT
True.
CT number: It is the same as Hounsfield units.
True.
The CT number of Fat is about - 400.
FALSE. -60 to -150 HU
A magnification factor of 1000 or more is used in the calculation of CT number.
FALSE. MULTIPLICATION NUMBER.
There is no difference between the CT numbers of gray and white matter in the brain.
False: The CT number of white matter is 20-30 and that of gray matter is 35-45.
The CT number of water is - 500.
False: The CT number of water is 0 and that of air is -1000.
CT number represents the linear attenuation coefficient in each pixel.
True.
CT numbers of tissues vary depending on the KV and filtration of the x-ray beam
True.
It is necessary to use a CT number higher than bone to image materials that have a higher linear attenuation coefficient.
True.
The CT number of air is -1000
True.
The CT number of contrast is higher than that of bone.
True.
A voxel is a three-dimensional region in the image display.
FALSE. VOXEL is a 3D region in the SCAN MATRIX
CT Image reconstruction involves a correction for the polychromatic nature of the beam.
True.
An image can only be reconstructed from data collected from a full 360° rotation of the gantry.
FALSE. You can reconstruct down to 180 degrees.
Fourier transformation can be used for image processing in CT.
True.
CT Detector collimation controls the size of a pixel.
False. The size of the image is determined by the computer programme.
Iterative reconstruction is the most commonly used method for image reconstruction.
False. Filtered back projection.
Digital subtraction is used in all CT image reconstruction.
False.
The width of the x-ray beam determines the size of the CT voxel.
TRUE.
A voxel represents a definable region within a CT slice matrix.
TRUE.
Noise is inversely proportional to the square root of the number of photons.
TRUE.
Applying a weighting factor compensates for the difference between the size and the shape of the scanning beam and the CT picture matrix.
TRUE.
The weighting factor is constant throughout each complete CT scan.
FALSE.
The physical density of its contents is the only factor that determines the CT number of a voxel.
FALSE: The CT number is determined by the attenuation of the x-ray beam which in turn is determined by physical density and atomic rtimber.
A pulse height analyser is used in CT image reconstruction.
D.
A voxel is a group of four adjacent pixels.
False.
Helical scanners: The pitch of the scanner can be defined as table-top movement per rotation multiplied by slice thickness.
False:The pitch of the scanner can be defined as table-top movement per rotation DIVIDED by slice thickness.
Helical scanners: The voxel size in the transaxial plane is determined by the matrix size and the field of view.
True.
Helical scanners: Helical scanners in general have faster acquisition times compared to single slice
scanners.
True.
Helical scanners: Movement artefacts are generally lower in images obtained from helical scanners compared to single slice scanners.
True
Helical scanners: The slice width cannot be less than the detector width.
True.
The effect of noise is reduced by using a narrower window while displaying the CT images.
False:The effect of noise is increased by using a narrower window because each grey level would represent a smaller range of CT numbers.
CT Contrast in the image is reduced by noise.
True
The effect of noise is decreased by increasing CT slice thickness.
True
Increasing the pixel size decreases CT spatial resolution.
True
Increasing the detector element size decreases the spatial resolution
True
Image quality in CT: Cupping is caused by detector malfunction.
False: Cupping is caused by beam hardening.
The spatial resolution of CT is affected by slice width.
True
CT Window level determines the number of shades of grey that would be displayed.
False: Window width determines the number of shades of grey that would be displayed
Compared to film screen radiography, line pair resolution is better in CT.
False: Line pair resolution in CT is poorer than that of film screen radiography and is only about 1 lp/mm as compared to upto 15 lp/mm in film screen radiography.
Noise in CT makes low-contrast objects difficult to distinguish.
True
CT Pixel size is generally about 1mm.
False: Pixel size is generally less than 0.5mm.
Decreasing pixel size increases the spatial resolution of CT.
True: The spatial resolution of CT improves, providing all other factors like number of detectors, size of detectors, focal spot size, etc. remains unchanged.
Increasing CT voxel size increases spatial resolution.
False.
Increasing pitch increases CT image unsharpness.
True
Decreasing mA decreases image noise.
False: Increasing mA increases the number of photons producing the image hence the image noise decreases.
Partial volume effect is reduced by using thicker CT slices.
False:The partial volume effect is due to averaging of the attenuation coefficient of different objects within a voxel. Using thinner slices can reduce this.
Regarding CT:
A. Resolution can be improved by magnification of the subject.
B. Air is used as a negative contrast agent.
C. Image quality is limited by quantum mottle.
All TRUE.
CT: Reducing beam filtration increases beam hardening artefacts.
True.
CT: Cardiac motion produces streak artefacts.
True.
CT: Geometric artefacts are caused by faulty detectors.
FALSE. RING ARTEFACT.
CT: Cone beam artefact is due to beam divergence in the x-axis.
FALSE. Z AXIS.
CT: Ring artefacts are most commonly seen in scanners that have fixed detectors.
False. Rotating detectors.
Regarding partial volume effect:
A thin high-contrast structure that crosses the transaxial plane at an oblique angle might disappear completely.
It is increased when the slices get thinner.
False: The thin high contrast structure that crosses the transaxial plane at an oblique angle (e.g. vessel filled with contrast) will appear larger.
False:The partial volume effect is reduced when the slices get thinner.
Regarding partial volume effect:
A. It reduces the visibility of low-contrast details.
B. A high-contrast object that is smaller than the voxel will appear larger on the image.
C. It is due to the averaging of CT numbers in each voxel.
All True.
CTDI is a measure of the radiation dose from the whole examination.
False: CTDI is a measure of the dose from a single rotation of the gantry.
CTDI varies with slice width.
False: CTDI is constant with slice width.
CTDI is measured in mGy cm.
False: CTDI is measured in mGy.
CTDI is measured using a pencil ionization chamber.
True.
CTDlvol is derived by multiplying CTDlw with pitch.
False. CTDI(vol) = CTDI(weighted) / pitch
Where pitch = mm per rotation / slice thickness (mm)
In helical scanning: The position of the reconstructed segment can be selected retrospectively.
True
In helical scanning: The slice width can be smaller or larger than the detector width.
False: The slice width cannot be less than the width of the detector.
In helical scanning: Keeping all other parameters constant, increasing pitch reduces exposure time.
TRUE.
In CT imaging, pitch is defined as the ratio of the table movement per rotation to the slice thickness. It influences how the scan is performed and directly impacts the exposure time.
When the pitch is increased (i.e., the table moves further per rotation of the X-ray tube), the slices are spaced farther apart. This means that for the same scan length, the X-ray tube is on for a shorter period during each rotation.
As a result, increasing pitch reduces the exposure time for each rotatio
In helical scanning: Keeping all other parameters constant, increasing pitch increases patient dose.
False: Increasing pitch decreases patient dose.
In helical scanning: Keeping all other parameters constant, increasing pitch decreases resolution.
True
- Spatial resolution in CT scanning is affected by:
A Pixel size.
B. Field of view.
C. Matrix size.
D. Algorithm used.
E. Beam filtration.
All True except BEAM FILTRATION.
The biggest contributor to CT image noise is electronic noise produced in the measuring system.
False: Electronic noise is the least significant contributor to image noise.
Quantum noise is increased by increasing the CT field of view (FOW).
False: Quantum noise is decreased by increasing FOV.
Quantum noise is increased by using a larger CT matrix.
TRUE.
Using a larger matrix means dividing the scanned area into smaller voxels (volume pixels). As a result, the same amount of radiation (or photons) is distributed over more voxels. This decreases the number of photons contributing to each voxel, increasing quantum noise.
For single slice CT scanners, increasing the pitch increases noise.
False: Pitch does not affect noise in single slice scanners
For multi-slice CT scanners, increasing the pitch increases noise.
True.
The DLP of a CT scan is calculated by multiplying weighted CTDI (CTDlw) with the total length of scan (L).
FALSE. CTDI(vol) x scan length L
Where CTDIvol = CTDIw / Pitch
Pitch = mm per rotation / slice thickness (mm)
CT: Conversion coefficients to derive effective dose from DLP are independent of scanner design.
False: There are differences in conversion coefficients for single and multi-slice scanners.
CT: Organs in the pelvis have a low E/DLP factor.
FALSE. False: Organs in the pelvis have a high E/DLP factor
CT: Conversion coefficients to derive effective dose from DLP depend on body region.
True: Conversion coefficients to derive the effective dose from DLP depend on body region and scanner design.
CT: Tissues and organs in the head have a low E/DLP factor.
True.
CT Detectors: Ionization chambers have a detection efficiency of about 40%.
False: Ionization chambers had a detection efficiency of about 60%.
CT Detectors: CT detectors need to have a low dynamic range to improve resolution.
False: CT detectors need a wide dynamic range to improve resolution
CT Detectors: In modern scanners, the individual detectors need to be as big as possible to reduce scan time.
False: Detectors need to be as small as possible to improve resolution. Scan time is not affected by size of individual detectors.
CT Detectors: Bismuth germinate may be used as a scintillant in solid state detectors.
TRUE.
CT Detectors: The overall efficiency of solid state detectors is compromised as they have to be separated to prevent light cross over:
TRUE.
The following are used for the calibration of the CT number scale of the scanner:
Iodine
Air
Water
Bone
Fat
Only WATER (0) and AIR (-1000)
- Regarding CT scanners:
A. Gas filled detectors are more efficient than solid state detectors.
B. The anode cathode axis of the x-ray tube is perpendicular to the fan beam.
C. The fan beam is collimated such that it is half the width of the patient.
D. The axis of rotation is called the z-axis.
E. Tube loading is much higher compared to plain x-rays.
- Regarding CT scanners:
A. Gas filled detectors are more efficient than solid state detectors. FALSE
B. The anode cathode axis of the x-ray tube is perpendicular to the fan beam. TRUE
C. The fan beam is collimated such that it is half the width of the patient. FALSE
The fan beam is wider than the widest cross section of the patient
D. The axis of rotation is called the z-axis. TRUE
E. Tube loading is much higher compared to plain x-rays. TRUE.
Regarding CT artefacts: Beam hardening is the same throughout the field of view for a given patient.
FALSE.
Tube current modulation is used to correct CT beam hardening artefact.
False: Tube current modulation (mA modulation) is used to correct the ‘photon starvation artefact’.
Compared to other metals, titanium is known to cause more artefacts.
False: Titanium causes fewer artefacts than other metals.
CT contrast agents do not produce artefacts.
False: A high concentration of contrast agent produces streak artefacts similar to metal.
Helical scanning is less susceptible to artefacts caused by patient motion than axial scanning.
True
The following artefacts are manifested as streaks in the image:
A. Inadequate field of view.
B. Photon starvation.
C. Motion.
D. Cone beam effects.
E. Beam hardening.
All True
A. Inadequate field of view:
True. If the scanned object extends outside the field of view, it can lead to streak artifacts due to data truncation.
B. Photon starvation:
True. Photon starvation occurs when insufficient X-rays pass through highly attenuating regions, leading to streaks, particularly in dense areas like bone.
C. Motion:
True. Patient motion during the scan causes misregistration of data, resulting in streak artifacts.
D. Cone beam effects:
True. In cone-beam CT, divergence of the X-ray beam can lead to incomplete or inaccurate data sampling, causing streak artifacts.
E. Beam hardening:
True. Beam hardening occurs when lower-energy photons are absorbed more than higher-energy photons as the beam passes through dense materials, creating streak artifacts in the image.
Dose length product (DLP) is inversely proportional to pitch.
TRUE.
DLP = CTDIvol x L
= (CTDI/Pitch) x L
So inversely proportional
CTDlvol is directly proportional to pitch.
False: CTDlvol is CTDIw / Pitch.
So INVERSELY proportional to pitch.
CTDlw of the head is lower than that of the body (for the same mAs and kVp).
TRUE.
DLP is directly proportional to the scanned length.
TRUE.
DLP = CTDIvol x L
On an average, the effective dose for the head is lower than that for the body.
True: The effective dose is relatively lower due to the lower radiosensitivity of the brain tissue.
CTDI is measured in mGy cm3
FALSE. CTDI is measured in mGy.
The effective dose is measured in mSv.
True
DLP is measured in mGy cm.
True. DLP is measured in mGy cm.
The dose area product is measured in mGy cm2.
True.
It represents the total radiation dose multiplied by the exposed area of the patient. DAP accounts for both the dose delivered and the area irradiated, making it a useful metric for estimating the overall risk of radiation exposure.
E/DLP (DLP to effective dose conversion coefficient) is measured in mSv (mGy cm-1).
E/DLP is measured in mSv / (mGy ∙ cm)
In CT images: Noise is inversely proportional to the number of photons.
FALSE. INVERSE SQUARE ROOT OF PHOTONS
CT: Doubling the mA reduces the noise by a factor of 2.
False. Reduces noise by a factor of square root of 2 = 1.4
CT: Halving rotation time decreases noise by a factor of the square root of 2.
False. Halving rotation time INCREASES noise by a factor of square root 2
Keeping everything else constant = less exposure time = few photons = INCREASE in noise.
CT Pixel size is generally less than 0.5mm.
True.
Increasing CT slice thickness decreases noise.
True.
CT numbers for the majority of organ soft tissues are in the range of 0-70.
True
CT number range for lung -900 to -1000
True
CT number of blood is similar to that of soft tissue.
True
CT number of fat is between -60 to -150
True
CT number of grey matter in the brain is between 35 - 45.
White matter is lower 20 - 30
TRUE.
Keeping all things constant: Doubling mA doubles the CT patient dose.
True
Keeping all things constant: Halving rotation time halves the dose.
True
Keeping all things constant: Doubling the pitch halves the dose.
True
The European guidelines on quality criteria for computed tomography (EUR 16262 EN)
A. A guidance on image quality and radiation dose on a generic examination by examination basis.
B. Guidance on structures that should be visible for a given type of examination.
C. A qualitative guide to the degree of clarity of structures to be expected.
D. Examples of good imaging techniques and settings.
E. Reference dose values in terms of CTDlw and DLP.
ALL TRUE.
CT: ECG gating requires the addition of extra hardware and software to existing scanners.
True.
CT: ECG gating can only be done prospectively.
False: ECG gating can be done prospectively or retrospectively.
CT: Retrospective ECG gating always results in a lower dose to the patient compared to ungated scans.
False: There is no dose reduction in retrospective gating.
CT: ECG gating decreases image degradation due to cardiac motion
True.
CT: In prospective gating, most of the image acquisition is done during systole.
False.
The typical effective dose for routine cardiac CT angiography is comparable to that of abdominal-pelvic CT
True. This is in the region of7-13 mSv.
Cardiac CT: Dose can be decreased by increasing pitch.
True
Regarding cardiac CT: Decreasing x-ray current during phases of the cardiac cycle is effective in reducing dose
True: Images acquired during these phases are of lower quality and therefore deemed to be of less value for interpretation.
Regarding cardiac CT: f the patient has a higher heart rate, increasing the pitch is a useful dose reduction technique.
True: This is a useful feature of dual-source cardiac CT where linking pitch to a patient’s heart rate can effectively reduce the dose and also obviate the need for a heart rate lowering drug such as beta-blockers.
Regarding cardiac CT: Dual source CT means that one x-ray tube is used with two sets of x-ray detectors.
False: It is 2 sets of x-ray tubes and 2 sets of x-ray detectors.
- The following are effective dose reduction methods in cardiac CT:
A Tube current modulation.
B. Decreasing tube current during phases of cardiac cycle.
C. Matching the pitch to the patient’s heart rate.
D. Increasing the scanning time.
E. Reducing pitch.
All true except increasing scanning time and reducing pitch
Cardiac CT: It requires a low temporal resolution to image the moving heart.
False: In fact, the primary challenge of imaging a beating heart in a system is to have a high temporal resolution.
Cardiac CT: Imaging is primarily directed at acquiring images during the systolic phase.
False: It is the diastolic phase as this is the most quiescent part of the cardiac cycle.
Cardiac CT: Spatial resolution is not as important as temporal resolution in cardiac CT
False: It is just as important as one must be able to resolve fine structures such as the coronary artery segments.
Cardiac CT: The faster the gantry rotation time, the greater the temporal resolution achieved.
True.
Cardiac CT: Prospective ECG triggering acquisition reduces the radiation exposure.
True.
Cardiac CT: In prospective ECG gating, the scanner starts at a preset point from the R-R interval.
TRUE.
Cardiac CT: The retrospective gating mode of acquisition has a higher radiation dose compared with prospective gating.
True: This is because data are acquired continuously during the cardiac cycle and data from ECG monitoring are retrospectively used for image reconstruction.
Cardiac CT: Multiple-segment reconstruction can result in misregistration and degrade spatial resolution.
True: This is one of the limitations of the multiple-segment reconstruction approach.
Cardiac CT: Partial scan reconstruction achieves high temporal resolution.
False: This is one of the major limitations of partial scan reconstruction and is due to the gantry rotation time. Higher temporal resolution is achieved with the multiple-segment reconstruction approach.
Cardiac CT: Radiation dose is inversely proportional to pitch.
True.
Stable lighter nuclei contain nearly equal numbers of protons and neutrons.
True
Stable heavier nuclei contain greater proportion of protons than neutrons.
False: Stable heavier nuclei contain greater proportion of neutrons.
Isotopes have the same number of protons, chemical, and metabolic properties.
True
Isotopes have different number of neutrons, mass number, density, and physical properties.
True
Unstable radioactive nuclei have proton or neutron excess or deficit and decay until they become stable.
True
All radionuclides used for medical imaging are produced artificially.
True
Molybdenum-99 (99Mo) is unstable as it is neutron deficient.
FALSE: 99Mo is made by ADDING a neutron to 98Mo in a nuclear reactor
hence it is unstable with an excess of neutron (98Mo + n -> 99Mo).
Fluorine-18 (18F) is unstable due to excess of neutron.
False: 18F is made in a cyclotron by an additional proton being forced into the stable nucleus of 180 which in return knocks out a neutron hence making the nucleus neutron deficient (18O + p ->18F + n).
99Mo can be extracted from the spent fuel rods of nuclear reactors.
True: 238U -> 99Mo + other fission by products.
Gallium-68 (68Ga) is produced from a germanium-68 (68Ge) generator.
Germanium motherland
Child went to the Gally’s for execution
True:68Ga is a daughter product of 68Ge.
In beta plus decay, the atomic number of the daughter nucleus increases by 1.
False.
In beta minus decay, the atomic number of the daughter nucleus increases by 1.
True. Atomic number increases by 1 and the atomic mass remains unchanged in the daughter nucleus.
The majority of the metastable radionuclides undergo isomeric transition.
True
In electron capture, the atomic mass decreases by 1.
False: In electron capture, the atomic number reduces by 1 whilst the atomic mass remains unchanged in the daughter nucleus.
Radionuclides which undergo internal conversion can emit both photoelectrons and characteristic x-rays.
True: Examples of such radionuclides are iodine-123 and iodine-125.
Internal Conversion (IC) occurs when an excited nucleus transfers its energy directly to one of the atom’s orbital electrons, typically from the K-shell or L-shell, ejecting the electron from the atom. This ejected electron is called a photoelectron.
Gamma rays emitted for a given radionuclide have a few specific energies which are characteristic of that nuclide.
True.
The most energetic beta rays only have a range of a few millimetres in tissue.
True.
Beta radiation emits at specific energies like gamma rays.
False: Beta rays emit a continuous spectrum of energies up to its maximum energy.
A positron combines with another positive electron to undergo annihilation to emit two photons of 511keV travelling in opposite directions.
FALSE. False: Positive beta particle combines with a negative electron to undergo annihilation
Re: Positron emitters: They are produced in a cyclotron.
TRUE
Re: Positron emitters:
Upon decay they emit a positive beta particle which combines with a nearby negative electron.
Positron annihilation emits two gamma photons of 511keV
They may be used in positron emission tomography (PET) imaging.
ALL TRUE
Radioactive decay: It is a deterministic process governed by the laws of chance.
False: It is a stochastic process governed by the laws of chance.
Radioactive decay: It is possible to predict the next disintegration within a sample of unstable nuclei.
False: It is impossible to predict the next disintegration in a given sample.
Radioactive decay: The decay rate is measured in the SI unit of millisievert (mSv).
False: The rate of decay is measured in becquerel (Bq) where 1Bq is equivalent to 1 disintegration per second.
Radioactive decay: It is possible to predict the reduction of radioactivity in a given time interval.
True.
Radioactive decay: The count rate measured by a radiation detector is less than the actual radioactivity.
True: A sufficient proportion of the rays usually miss the detector or it may pass through undetected hence the count rate is less than the activity
Effective half life is dependent of the biological half-life of the radiopharmaceutical
TRUE. 1/ effective = 1/bio + 1/physical
Effective half life is independent of the physical half-life
FALSE. 1/ effective = 1/bio + 1/physical
Effective half life: is the same in everyone for a given radiopharmaceutical.
False:The metabolic process of eliminating and excreting radiopharmaceutical varies between everybody.
Effective half life is not affected by the patient’s renal function.
False.
Effective half life: The effective half-life is always less than the biological half-life or the physical half-life.
True.
Ideal properties of radiopharmaceuticals: A physical half-life as short as possible.
False:The half-life should be suitable for the examination.
Ideal properties of radiopharmaceuticals: It localizes largely and quickly to the tissues of diagnostic interest.
True.
Ideal properties of radiopharmaceuticals: It emits gamma radiation only.
True: Hence scatter can be eliminated by energy discrimination with a pulse height analyser.
Ideal properties of radiopharmaceuticals: A pure gamma emitter with energy emission greater than 300keV.
False: It should be a pure gamma emitter but with energy emission between 50-300keV.
Ideal properties of radiopharmaceuticals: It is easily made and readily available at the hospital site.
True.
Desirable properties of radioactive nuclei: To decay to a stable daughter product or at least one with a very long half-life.
True
Desirable properties of radioactive nuclei: Attaches easily and firmly to the pharmaceutical with no effect on its metabolism.
True
Desirable properties of radioactive nuclei: To emit gamma rays with energy greater than 300KeV.
False:An ideal energy emission is around 150KeV where it is high enough to exit the patient but low enough to be collimated and detected.
Desirable properties of radioactive nuclei: High radioactive concentration in terms of high concentration per unit volume.
True
Desirable properties of radioactive nuclei: Delayed elimination from the body with an effective half-life as long as possible.
False: An ideal radiopharmaceutical should be eliminated from the body with an effective half-life as long as the duration of the examination in order to reduce the dose to the patient.
Technetium-99m: is produced in a generator.
True.
Technetium-99m: emits gamma rays principally of 0.140MeV.
True. Desirable as around the 150keV range
Technetium-99m: has a physical half-life of 6 days.
FALSE. SIX HOURS.
Technetium-99m: It is a daughter product of the parent radionuclide Iodine 311.
FALSE.
Mo-99 (Beta MINUS decay) → Tc-99m (metastable state, gamma-emitting)
Tc-99m then decays to Tc-99 by emitting gamma radiation.
Technetium-99m: is a product of electron capture decay.
FALSE.
Mo-99 (Beta MINUS decay) → Tc-99m (metastable state, gamma-emitting)
Tc-99m then decays to Tc-99 by emitting gamma radiation.
Technetium generator: In transient equilibrium, the daughter and the parent appear to decay together with the half-life of the parent.
True
Technetium generator: shielded with lead or depleted uranium.
True
Technetium generator: The parent 1311 is absorbed within the exchange column of aluminium beads.
False: The parent radionuclide is 99Mo.
Technetium generator: Technetium is eluted with sterile water.
False: It is eluted with sterile saline solution.
Technetium generator: The lead shielding and the metal container are reusable.
True
Krypton-81 m (81Krm) has a half-life is…
Krypton-81 m (81Krm) has a half-life of 13 SECONDS.
Krypton-81 undergoes beta MINUS decay to produce Rubidium-81
81yo superman only takes an unlucky 13secs to…
Krypton-81m (81Krm) is used for pulmonary ventilation studies.
True
Fluorine-18 (18F) has a half-life of…
110 minutes.
18O + p → 18F + n
18F → 18O + positron
Technetium-99m (99Tcm) has a half-life of…
6 hours…
Molybdenum-99 (99Mo) has a half-life of…
67 hours.
Mo98 +n bombardment -> Mo99
Mo99 beta MINUS decay into Tc 99m
Technetium-99 has a half life of…
200,000 years.
Iodine 123 has a half of..
13 hours!
I-123 has a gamma emission of 159 keV
Decaying by electron capture to form Te-123.
Tellurium-123 de-excites by emitting a gamma photon of 159 keV to reach its stable ground state.
lodine-123 (1231) labelled to hippuran is used for renal studies.
True
And has a half life of 13 hours!
Xenon-133 (133Xe) has a half life of
5 days
Irradiate uranium-235 to produce xenon-133
Beta minus decay into Cs 133
and in the process, it emits gamma radiation (γ-rays) with an energy of 81 keV.
Xenon-133 (133Xe) is used in lung ventilation imaging.
Lung ventilation imaing
Gallium-68 (68Ga) half life of…
Half-life of gallium-68 is 68 minutes
Gallium-68 undergoes beta-plus decay to form stable Zinc-68
Gallium-68 is typically produced from its parent isotope, Germanium-68 , through radioactive decay or via proton bombardment in a cyclotron.
Gallium 68 is used in the PSMA inhibitor for imaging prostate cancer
True
Gallium-68 (68Ga) is used to detect tumours and abscesses.
True
Thallium-201 half life of
73 hours
Production:
Thallium-201 is not naturally occurring and is produced by proton bombardment of stable Mercury-201 in a cyclotron.
Decay Mode:
* Electron capture (EC) to Mercury-201 (^{201}Hg)
* Emits X-rays (69–80 keV) and gamma photons (135 keV & 167 keV)
Thallium-201 in Myocardial Perfusion Imaging
True. It behaves like potassium (K⁺) in the body and is actively taken up by myocardial cells via the sodium-potassium ATPase pump.
Common Cyclotron-Produced Radiopharmaceuticals
Cyclotron Produced Radiopharmaceuticals in PET
Cyclotron Produced Radiopharmaceuticals in SPECT
Indium 111
Iodine 123
Thalium 201
Gamma camera collimators: In a parallel hole collimator, the field of view and the in-air sensitivity are the same at all distances.
TRUE
Gamma camera collimators: A divergent hole collimator obtains a larger field of view and magnifies the image.
False: A divergent hole collimator does allow a large field of view to be obtained but it minifies the image.
DIVERGING AWAY FROM DETECTOR
Gamma camera collimators: A convergent hole collimator minifies the image when a small field of view is acquired.
False: A convergent hole collimator magnifies the image when a small field of view is
obtained.This is used in imaging small organs or children.
CONVERGING AWAY FROM DETECTOR
Gamma camera collimators:Both the divergent hole and convergent hole collimators suffer from geometric distortion with deterioration of spatial resolution at the edge of the field.
TRUE.
Gamma camera collimators: A pinhole collimator produces magnified and inverted images.
True: It is used in imaging superficial small organs such as the thyroid.
Regarding the gamma camera crystal:
The crystal is made of SODIUM iodide and activated with a trace of thallium.
TRUE. SODIUM IODIDE USED IN SPECT.
NOT CESIUM IODIDE
High light output: NaI:TI (with thallium dopant) produces a bright flash of light when exposed to gamma radiation.
High light output: NaI:TI (with thallium dopant) produces a bright flash of light when exposed to gamma radiation.
Fast scintillation response: NaI is relatively quick in terms of light emission.
Regarding the gamma camera crystal: It is composed of multiple small crystals.
False: It is one large crystal.
Gamma camera crystal: Emits approximately 5000 light photons when struck by a gamma photon.
True.
Gamma camera crystal: a flat transparent light guide can maximize transfer of light from the crystal to the photomultiplier.
True.
Gamma camera crystal: It is robust and waterproof.
FALSE.
It is fragile, hygroscopic (EASILY absorbs moisture) and easily damaged by temperature change.
Gamma camera: Spatial resolution improves by rejecting scattered gamma rays.
TRUE.
Gamma camera: The typical energy window is ±10% of the photopeak.
TRUE
Gamma camera: Two radionuclides can be imaged simultaneously.
TRUE
Gamma camera: The stored digital image can be manipulated.
TRUE
Gamma camera: Digital cameras do not require photomultiplers.
False: Photomultiplers are a key component in a gamma camera.
Gamma camera: The purpose of the collimator is to remove scattered radiation.
False: Collimator locates the radioactive source within the patient along its line of sight, without it no image would be formed.
Main purpose is to remove scatter is the pulse height analyser
Gamma camera: The spatial resolution is comparable to that of a CT scanner.
FALSE.
Gamma camera: The purpose of the pulse height analyser is to filter out scattered radiation.
True.
Gamma camera: The photomultiplier tubes amplify the signal by a series of dynodes.
True: The numbers of electrons are increased at each dynode, producing a cascade effect.
Gamma camera: Variation in the image of a uniform source is caused mainly by variations in the thickness of the Nal (TI) crystal.
False:The main cause of variation in the image is electronic in nature.
The spatial resolution of the gamma camera is affected by: The thickness of the crystal.
True: Resolution improves with a thinner crystal.
The spatial resolution of the gamma camera is affected by: The diameter of the hole of the collimator.
True: Spatial resolution improves with a smaller of the width of the holes in the collimator.
The spatial resolution of the gamma camera is affected by: The length of the hole of the collimator.
True:The longer the holes of the collimator; the better the spatial resolution.
The spatial resolution of the gamma camera is affected by: The count rate.
False: Count rate affects the brightness of the pixel and not the spatial resolution if acquired over the same period of time.
The spatial resolution of the gamma camera is affected by: The number of photomultiplier tubes.
False: The photomultiplier tubes acts as an amplifier and does not affect the spatial resolution.
Quality control for the gamma camera:
Spatial resolution is assessed by using line source to give the line spread function
True.
Spatial resolution is assessed by using line source to give the line spread function
Quality control for the gamma camera:
Uniformity of field is assessed by imaging a line source.
False: Gamma Camera uniformity of field is assessed by using a flood field phantom.
Quality control for the gamma camera:
Typical system uniformity is 20%.
Typical Gamma Camera Uniformity is 2%
Quality control for the gamma camera:
Intrinsic resolution is better than the system resolution.
True: The intrinsic resolution of a gamma camera is the best resolution a camera can achieve.
Quality control for the gamma camera:
A cracked crystal will not show as a defect.
False: A cracked crystal appears as a defect in the image.
SPECT: It consists of a gamma camera with a collimator rotating around a patient on a couch.
TRUE.
SPECT: The camera rotates continuously to acquire images.
True: You can have continuous or set and shoot acquisition.
SPECT: It requires fewer counts than conventional static imaging.
True. Decent contrast but poor spatial resolution. Few counts also mean more noise.
SPECT: The same number of counts can be acquired in half the time by using a double headed camera.
True.
SPECT: Sensitivity decreases when a double- or tripled-headed camera is used.
False:The counts per second per MBq received by a double- or triple-headed camera will be greater than that of a single-headed camera. Hence the system sensitivity will increase.The sensitivity of each individual head of the camera will not be affected.
Advantages of SPECT over planar imaging: It has the potential to correct for attenuation.
TRUE.
This correction is especially useful in regions of the body with high-density tissues (like bones), which can attenuate the gamma rays.
Advantages of SPECT over planar imaging: There is an increase in spatial resolution
FALSE.
SPECT generally does not provide higher spatial resolution compared to planar imaging because it acquires data from multiple angles and reconstructs a 3D image, but this process introduces some blurring.
CONTRAST RESOLUTION IS IMPROVED.
Advantages of SPECT over planar imaging: There is an increase in contrast.
By using multiple projections and reconstructing a 3D image, it can help separate structures that might overlap in a planar image, improving contrast between different tissues or abnormalities.
Advantages of SPECT over planar imaging: There is a more noise.
True. Noise is increased in SPECT as the images are made up of fewer photons.
Advantages of SPECT over planar imaging: It has fewer equipment related artefacts.
False.
SPECT can actually have more equipment-related artifacts compared to planar imaging due to its complex reconstruction process and motion artifacts (if the patient moves during scanning). Additionally, the system geometry and detector configuration can introduce certain types of artifacts, like ring artifacts.
SPECT: Filtered back projection may be used in image formation.
True.
SPECT: Iterative reconstruction produces fewer artefacts and can correct attenuation more accurately than filtered back projection.
True.
SPECT: Superimposition of overlying structures cannot be resolved.
False: Overlying structures are resolved during 3D reconstruction.
SPECT: Reconstruction can be performed through any plane.
True
SPECT: Planar views are reconstructed to form a 3D image.
True.
SPECT image resolution can be improved by:
Using a 128 x 128 matrix compared to a 64 x 64 matrix.
True.
A 128 x 128 matrix provides higher resolution than a 64 x 64 matrix because it increases the number of pixels (or voxels in 3D) used to represent the image. A higher matrix size leads to finer details and a better representation of the anatomical structures in the SPECT image.
SPECT image resolution can be improved by: Increasing the administered activity of a radiopharmaceutical.
False: This will lead to an increase of the count of the image REDUCING NOISE but the resolution is a factor of the system and not the patient.
SPECT image resolution can be improved by: Using a low resolution collimator.
False: Resolution improves with a high resolution collimator.
SPECT image resolution can be improved by: Using a smooth reconstruction filter.
FALSE.
A smooth reconstruction filter (such as a low-pass filter) typically reduces high-frequency details in an image,
reduces sharpness and can make the image appear smoother
but at the cost of lower resolution. While it can help reduce noise,
it doesn’t improve resolution; it often blurs the image to enhance visual quality.
SPECT image resolution can be improved by: not reducing noise with a mathematical filter.
False. SPECT image resolution can be improved by reducing noise with a mathematical filter.
Reducing noise with a mathematical filter (such as a high-pass filter or a noise-reducing algorithm) is important for improving image quality and achieving better resolution.
Not reducing noise can increase noise levels, making the image appear grainy and lowering the effective resolution.
Necessary to perform SPECT: A triple-headed camera.
FALSE
Necessary to perform SPECT: camera system capable of rotating around the patient.
TRUE.
Necessary to perform SPECT: A radionuclide which emits monoenergetic gamma photon energy only.
False.
A monoenergetic gamma photon is not required for SPECT, although it is ideal for better image quality. In practice, many commonly used SPECT radionuclides emit gamma photons with some energy variation (such as Technetium-99m). The energy spectrum of the emitted photons may not be strictly monoenergetic, but it is typically narrow enough to allow for effective imaging.
Necessary to perform SPECT: A radiopharmaceutical specifically designed for use with SPECT.
True
Necessary to perform SPECT: A radiopharmaceutical whose distribution within the patient is fixed.
False.
The distribution of a radiopharmaceutical within the patient is not necessarily fixed. It often changes over time, depending on the biological processes and pharmacokinetics of the radiopharmaceutical.
PET images can give functional and physiological information.
True
PET images can be fused with CT images to allow location and visualization of such information within the patient’s anatomy.
True.
PET: Positrons are coincidentally detected.
False: PET detects the gamma rays emitted as a result of annihilation between positrons and electrons.
PET imaging is based on detecting an annihilation photon to locate the source of radioactivity within the patient
False: PET imaging is based on detected two annihilation photons in coincidence.
PET: Annihilation photons have energy of 0.51MeV.
True
PET: Most commonly used positron emitter in PET is 18F.
True.
PET: Annihilation photons are detected by a ring of detectors.
True.
PET: Scintillation detectors may be made from lutetium oxyorthosilicate.
True.
PET: 68Ga and 82Rb are also used in PET imaging.
True.
PET imaging can be combined with MRI images to assist the location of radioactivity within the patient’s body.
TRUE.
Ideal properties of PET scintillation detectors: Good energy resolution.
True
Ideal properties of PET scintillation detectors: High detection efficiency.
True
Ideal properties of PET scintillation detectors: A very short scintillation decay time.
True
A short scintillation decay time is crucial for fast timing and high count rates, which are necessary in PET imaging to reduce blurring and improve temporal resolution. Faster detectors improve coincidence timing resolution, which enhances time-of-flight (TOF) PET performance.
Ideal properties of PET scintillation detectors: High effective atomic number and physical density.
A high effective atomic number (Z) and physical density increase the probability of photoelectric absorption of 511 keV photons, improving detection efficiency. Materials like Lutetium Oxyorthosilicate (LSO) and Bismuth Germanate (BGO) are preferred for their high Z and density.
Ideal properties of PET scintillation detectors: High relative light output.
A high relative light output means the scintillator produces more visible light per detected gamma photon, which enhances the efficiency of the photodetector (e.g., photomultiplier tube or silicon photomultiplier). This leads to better energy resolution and signal quality.
Advantages of PET over SPECT: Collimators are not required for PET.
True.
Unlike SPECT, which uses physical collimators to limit the detection of gamma rays, PET does not require collimators. Instead, PET relies on coincidence detection of the two 511 keV annihilation photons emitted in opposite directions. This increases sensitivity compared to SPECT, where collimators block a large fraction of photons.
Advantages of PET over SPECT: Spatial resolution is superior to SPECT.
True.
* Coincidence detection provides better localization.
* PET detectors have finer intrinsic resolution than SPECT collimators.
* Time-of-flight (TOF) PET further improves resolution by refining the origin of annihilation events.
Typical PET resolution is 4–6 mm, while SPECT resolution is usually 8–12 mm (or worse, depending on collimator type).
Advantages of PET over SPECT: Image noise is less than SPECT.
True. MORE PHOTONS DETECTED.
Advantages of PET over SPECT: Radiation dose to patient is markedly reduced compared to SPECT.
FALSE.
PET tracers like ¹⁸F-FDG (~0.19 mSv/MBq) often have HIGHER radiation doses compared to
99mTc-based SPECT tracers (~0.007–0.01 mSv/MBq).
Advantages of PET over SPECT:
18F has a shorter half-life than 99Tcm.
TRUE.
110 minutes Vs 6 hours.
Nuc Med: The absorbed dose increases IN PROPORTION to: activity administered to the patient.
True.
D α A
where D = absorbed dose and A = administered activity.
Nuc Med: The absorbed dose increases IN PROPORTION to: The fraction taken up by the organ.
True.
D α f
where f = fraction of activity taken up by the organ.
Nuc Med: The absorbed dose increases IN PROPORTION to:
The effective half-life of the activity in the organ.
False: The absorbed dose does not increase in proportion with an increase in the energy of gamma radiation.
A longer effective half-life means the activity stays in the organ longer, leading to a higher total absorbed dose.
However, the relationship is not perfectly linear because radioactive decay is exponential, meaning the rate of decay slows over time.
Nuc Med: The absorbed dose increases IN PROPORTION to: The energy of the gamma radiation emitted from decay.
FALSE.
Gamma photons do not contribute directly to absorbed dose in a linear way because most of their energy escapes the body rather than being absorbed locally.
Nuc Med: The absorbed dose increases IN PROPORTION to: The renal excretion rate.
False: Increasing the renal excretion rate decreases the biological half live hence it reduces the absorbed dose.
Based on UK ARSAC DRLs:
The effective dose for a bone SPECT scan is 5.0 mSv
True. The effective dose for a bone SPECT scan is 5.0 mSv
Bone 5
Brain 8
Heart 10
Renal +lung 0.7-2.5
Based on UK ARSAC DRLs:
The effective dose for a 201Tl heart scan is 50 mSv,
False - The effective dose for a 201Tl heart scan is 11.2 mSv, not 50 mSv
Bone 5
Brain 8
Heart 10
Renal +lung 0.7-2.5
Based on UK ARSAC DRLs: Effective dose is around 8mSv for a brain scan.
True. The effective dose for a brain scan (e.g., 99mTc exametazime) is 7.0 mSv.
Bone 5
Brain 8
Heart 10
Renal +lung 0.7-2.5
Based on UK ARSAC DRLs:
The effective dose for renal studies (e.g., MAG3 renal imaging/renography) is up to 2 mSv
The effective dose for renal studies (e.g., MAG3 renal imaging/renography) is up to 2 mSv
Bone 5
Brain 8
Heart 10
Renal +lung 0.7-2.5
Based on UK ARSAC DRLs: Effective dose is up to 2mSv for lung scans.
True.
Bone 5
Brain 8
Heart 10
Renal +lung 0.7-2.5
Nuclear medicine: The ideal radionuclide emits both gamma and beta radiation.
False: Ideally should be a pure gamma emitter as beta radiation contributes to patient dose with no role in image formation.
Nuclear medicine: Lead aprons are effective and should be worn if gamma ray energies are greater than 140keV.
False: Lead aprons are ineffective against high energy gamma rays.
Nuclear medicine: Not all radioactive waste must be disposed of by a specialist waste contractor.
True.
Nuclear medicine: The photoelectric effect predominates when the photon energy is above 2MeV.
False: At such high energies, the contribution from photoelectric interactions is negligible.
Nuclear medicine: All radioactive administrations are contraindicated in women who are breastfeeding.
False.
For certain radiopharmaceuticals, no breastfeeding interruption is needed
Some radiopharmaceuticals require temporary breastfeeding interruption, while others may require complete cessation, particularly with long-lived radionuclides like Iodine-131 (¹³¹I)
Medicines (Administration of Radioactive Substances) Regulations (MARS) 1978 has been replaced with
The Medicines (Administration of Radioactive Substances) Regulations (MARS) 1978 has been replaced by the Ionising Radiation (Medical Exposure) Regulations (IR(ME)R) 2017 in Great Britain and the Ionising Radiation (Medical Exposure) Regulations (Northern Ireland) 2018 in Northern Ireland
An ARSAC certificate must be obtained for all procedures which use radionuclides.
False – An ARSAC certificate is required only for procedures involving the administration of radioactive substances that result in an effective dose greater than 1µSv
An ARSAC licence should be obtained by all employees working in nuclear medicine.
False. An ARSAC licence is only required for practitioners who are clinically responsible for justifying the administration of radioactive substances. Not all employees in nuclear medicine require a licence
The ARSAC clinical licences are valid for 5 years.
True. ARSAC clinical licences are typically valid for 5 years, unless a shorter duration is specified
The ARSAC research licences are valid for 2 years.
True – ARSAC research licences are valid for 2 years
Based on UK ARSAC Guidance: A licence covers all work involving radionuclides within the hospital.
False – A licence does not cover all work involving radionuclides within a hospital;
it is SPECIFIC to the APPROVED PROCEDURES and LOCATIONS
The application for an ARSAC licence must be signed by a Radiation Protection Advisor.
False – The application for an ARSAC licence does not need to be signed by a Radiation Protection Advisor (RPA). The licence application process involves different personnel, including the employer and supporting staff, but an RPA’s signature is not a requirement
The chief pharmacist’s (or equivalent individuals’) signature on the employer licence application form confirms they have satisfied themselves that sufficient and appropriate arrangements for
safe use of radiopharmaceuticals are in place.
There must be adequate scientific support in order for an ARSAC licence to be granted to an applicant.
True.
IR(ME)R requires that employers must ensure that suitable MPEs are appointed and involved in exposures involving the administration of radioactive substances. The MPE should advise the employer on compliance with IR(ME)R.
The ARSAC certificate is issued by the Department of Health.
True – The ARSAC certificate is issued by the Department of Health
It is the employer’s responsibility to ensure relevant clinicians possess an ARSAC licence.
True – It is the employer’s responsibility to ensure that relevant clinicians possess an ARSAC licence for justifying the administration of radioactive substances
It is the responsibility of the ARSAC licence holder to discharge a radioactive patient with the appropriate advice and hence protect the safety of the public.
True – The ARSAC licence holder is responsible for discharging a radioactive patient with the appropriate advice to ensure public safety
Radioactive Substances Act 1993 has been replaced with
Environmental Permitting (England and Wales) Regulations 2016 AND CORRESPONDING legislation in Scotland and Northern Ireland
Environmental Protection (England and Wales) Regulations replacing Radioactive Substances 1993 act:
It controls the accumulation, storage, and disposal of radioactive waste.
True – The act controls the accumulation, storage, and disposal of radioactive waste
Environmental Protection (England and Wales) Regulations replacing Radioactive Substances 1993 act:
It is enforced by the Environment Agency.
True – The act is enforced by the Environment Agency, which regulates the use, accumulation, and disposal of radioactive substances
Environmental Protection (England and Wales) Regulations replacing Radioactive Substances 1993 act:
Hospitals are exempted of registration under the Radioactive Substance Act 1993 for keeping any given amount of radioactive substance.
False – Hospitals are not exempt from registration under the Radioactive Substances Act 1993. They must comply with the relevant regulations governing the use and storage of radioactive substances
Environmental Protection (England and Wales) Regulations replacing Radioactive Substances 1993 act:
Once a hospital is registered, there is no stipulation or enforcement on the methods of radioactive waste disposal.
False – Once a hospital is registered under the act, there are strict stipulations and enforcement regarding radioactive waste disposal methods, ensuring safe handling and minimal environmental impact
Environmental Protection (England and Wales) Regulations replacing Radioactive Substances 1993 act:
All hospitals using radioactive substances are subjected to strict disposal limits for radioactive substances.
True – All hospitals using radioactive substances are subject to strict disposal limits, with regulatory oversight ensuring compliance with dose and disposal restrictions
Disposal methods of radioactive waste:
Gas can be disposed by venting it to the atmosphere.
True – Gas containing radioactive substances can be vented into the atmosphere, provided it meets regulatory limits and is handled through an extraction system.
Disposal methods of radioactive waste:
Aqueous liquid diluted with water can be disposed into the sewers.
True – Aqueous liquid waste may be diluted with water and disposed of into sewers, as long as it meets the permissible concentration limits
Disposal methods of radioactive waste:
Organic liquid must be disposed to an authorized contractor.
True – Organic liquid waste must be disposed of through an authorized contractor who is licensed to handle and process radioactive waste
Disposal methods of radioactive waste:
Solid waste must be disposed to authorized incinerators or waste contractors.
True – Solid radioactive waste must be disposed of via authorized incinerators or waste contractors in compliance with regulatory requirements
Disposal methods of radioactive waste:
Contaminated clothing and bedding is bagged and securely stored until the activity is sufficiently decayed for release to the laundry.
True – Contaminated clothing and bedding should be bagged and securely stored until the radioactivity has decayed to a safe level, at which point it may be sent to the laundry
Precautions in handling radionuclides:
Internal radiation occurs from accidental ingestion or inhalation of radionuclide.
True – Internal radiation exposure occurs from accidental ingestion or inhalation of radionuclides
Precautions in handling radionuclides:
Patients containing radioactivity are not a source of external radiation.
False: Patients containing radioactivity are a source of external radiation hence distance,
shielding, and time should be applied to protect staff and the public.
Patients containing radioactivity are a source of external radiation, especially for high-energy gamma emitters
Precautions in handling radionuclides:
2.5mm lead aprons are effective in providing adequate radiation protection when manipulating radiopharmaceuticals.
False – 2.5mm lead aprons are not effective for radiation protection when manipulating radiopharmaceuticals because lead aprons mainly protect against scatter radiation rather than direct exposure from high-energy gamma emitters
Precautions in handling radionuclides:
Personal protection should be made by distance, shielding, and time.
True – Personal protection against radiation should be implemented by using distance, shielding, and time as fundamental principles
Precautions in handling radionuclides:
Dose reduction is achieved by using forceps and syringe shields when handling radionuclides.
True – Dose reduction can be achieved using forceps and syringe shields when handling radionuclides to minimize direct hand exposure
Precautions in nuclear medicine:
Patient dose from a bone scan injection is reduced by encouraging high oral intake of water and by frequent micturation.
True: This will reduce the dose to the gonads and to the pelvic bone marrow in radionuclides which are excreted by the kidneys.
Precautions in nuclear medicine:
Children are given radiopharmaceuticals of higher activity than adults due to their increased metabolism in order to achieve an adequate diagnostic image.
False – Children are not given higher activity than adults to compensate for increased metabolism. Instead, pediatric dosing is scaled down based on body weight to achieve an adequate diagnostic image while minimizing radiation exposure
Precautions in nuclear medicine:
Female patients should avoid conception for a given period after the administration of a radionuclide with a long half-life.
True – Female patients should avoid conception for a specified period after administration of radionuclides with long half-lives, especially therapeutic isotopes like Iodine-131 and Strontium-89, due to their long biological clearance times
Precautions in nuclear medicine:
Examinations resulting in a foetal dose greater than 10mSv should be avoided in
pregnant patients.
True – Examinations resulting in a foetal dose greater than 10 mSv should be avoided in pregnant patients unless absolutely necessary
Precautions in nuclear medicine:
Cessation of breast feeding is not necessary when lactating mothers are given therapeutic doses of lodine-131
False – Cessation of breastfeeding is necessary when lactating mothers receive therapeutic doses of Iodine-131, as radioiodine is excreted in breast milk and can expose the infant to radiation
Nucmed: All doses must be as low as reasonably practicable (ALARP).
True.
Nucmed: Diagnostic reference levels are equivalent to dose limits.
False – Diagnostic Reference Levels (DRLs) are not equivalent to dose limits; they serve as guidelines to optimize imaging doses rather than hard limits
Nucmed: Diagnostic reference levels may be exceeded in tall obese patients.
True
Nucmed: Diagnostic reference levels are produced by Ionising Radiation Regulations 1999.
Administration of Radioactive Substances Advisory Committee (ARSAC) provides Diagnostic Reference Levels (DRLs) for common nuclear medicine examinations in the UK.
These DRLs are detailed in the ARSAC Notes for Guidance
Nucmed: Organ dose can be calculated by the Medical Internal Radiation Dose (MIRO) scheme.
True – Organ dose can be calculated using the Medical Internal Radiation Dose (MIRD) scheme, which estimates internal radiation dose from radiopharmaceuticals.
Concerning diagnostic ultrasound: It has a wavelength in soft tissue of 0.1-1.5 nanometres.
False: The wavelength in soft tissue is between 0.1-1.5 millimetres.
The ultrasound beam cannot be focused.
False: It can be focused either by
- applying an acoustic lens to the transducer or
- by using curved transducer crystals
- In array transducers focusing can also be achieved electronicall
Concerning diagnostic ultrasound: Ionization of soft tissue may occur at frequencies greater than 1MHz.
False: Only ionizing radiation, such as x-rays and gamma rays, can cause ionization in tissue. Ultrasound is a mechanical sound wave and therefore cannot cause this.
US uses frequencies between 2-15MHz
True.
US is audible
False:The upper limit of human hearing is 20KHz.
The speed of ultrasound remains constant through different tissue.
False
US: It has an average speed of 300m/s in soft tissue.
FALSE. The average speed of ultrasound in soft tissue is ~1540 m/s, not 300 m/s.
US: A change in acoustic impedance between two media causes refraction.
FALSE. Refraction occurs due to a change in sound speed when crossing an interface at an oblique angle, as per Snell’s Law.
US: The time gain compensator (TGC) can be used to decrease the amplitude of strong echoes behind fluid filled structures.
TRUE.
US: TGC is used to enhance echoes from deeper structures.
True.
US: Using tissue harmonic imaging in the obese patient can improve tissue contrast as it suppresses the effect of sidelobe and reverberation artefacts.
True
US: Ultrasound is a transverse wave
False: Ultrasound is a longitudinal wave; the molecules vibrate back and forth in the same direction as the wave is travelling.
US: The intensity of ultrasound is measured in watts per centimetre squared.
True
US: In pulse-echo imaging the depth of an interface d = ct, where c is the velocity of sound, and t is the time of travel of the pulse.
FALSE: This would actually give twice the depth as the pulse has travelled to the interface and returned in this time. D = ct / 2
Attenuation of ultrasound results in the heating of tissues.
true
The velocity of ultrasound in tissue is affected by the: Frequency or wavelength
FALSE.
US velocity is affected by temperature
True. Density decreases and stiffness increases so FASTER
US velocity is affected by tissue compressibility.
True. Compressibility is the inverse of stiffness (bulk modulus).
US velocity is affected by tissue density
True.
BUT Stiffness has a greater impact than density on sound velocity in soft tissues.
US: Magnitude of echoes is proportional to the sum of impedances of tissues.
False:The reflected intensity is related to the difference in impedance divided by the sum of impedances at an interface.
The acoustic impedance of a tissue is directly proportional to its density.
True.
Z = ρc
* Z = Acoustic impedance (kg/m²s)
* ρ = Density of the tissue (kg/m³)
* c = Speed of sound in the tissue (m/s)
At the soft tissue-air interface, over 99% of the energy is reflected.
TRUE.
The velocity of sound in tissue tends to increase with the density of the tissue.
False: Velocity of sound is inversely proportional to the square root of the tissue density.
To detect tissue boundaries with pulsed US: It is desirable that the incident beam strikes the tissue surfaces at right angles.
True
The acoustic impedance of a tissue is constant within the diagnostic frequency range.
True
To detect tissue boundaries with pulsed US:
B. The acoustic impedance on each side of the boundary should be the same.
False.
To detect tissue boundaries with pulsed US:
At least 5% of the incident beam must be reflected back to the transducer.
FALSE:
Reflection coefficients for all soft tissue interfaces are less than 5%,
e.g. soft tissue - muscle interface has a reflection coefficient of 0.04% !!!
To detect tissue boundaries with pulsed US:
There must be a difference between the product of density and propagation velocity for the tissues on each side of the boundary.
TRUE. Z = ρc
Z = ρc
* Z = Acoustic impedance (kg/m²s)
* ρ = Density of the tissue (kg/m³)
* c = Speed of sound in the tissue (m/s)
To detect tissue boundaries with pulsed US: The reflective surface must be stationary.
False: Heart valves are seen despite not being stationary.
In diagnostic ultrasound: velocity of sound in the liver is twice the velocity in muscle.
False:There is minimal change in velocity within soft tissues hence an assumption of 1540m/s is used.
Velocity of sound is dependent of the temperature.
True: For example the velocity of sound in water at 20°C is 1480m/s but is 1570m/s at
37°C.
The absorption of ultrasound in tissues is frequency dependent.
True: Absorption is a major component of the attenuation of ultrasound which is frequency dependent.
For a constant angle of incidence, the deviation of the refracted ultrasound beam will be greater at a soft tissue-bone interface than at a muscle-fluid interface.
True: The greater the difference in speed of sound between two media, the greater the degree of refraction.
The acoustic impedance of tissue is inversely proportional to its density.
Z = ρc
Z = ρc
* Z = Acoustic impedance (kg/m²s)
* ρ = Density of the tissue (kg/m³)
* c = Speed of sound in the tissue (m/s)
40% of ultrasound is reflected from a bone and muscle interface.
Approximately 40-45% of ultrasound is reflected at a bone-muscle interface, making the statement approximately correct
A frequency of greater than 10MHz is normally used for an abdominal scan.
FALSE.
Lower frequencies (e.g., 2-5 MHz) penetrate deeper but have lower resolution, which is essential for imaging deep abdominal structures like the liver, kidneys, and pancreas.
The maximum pulse repetition frequency (PRF) is limited by the maximum depth to be sampled.
True
US: Refraction is a cause of spatial artefacts.
True
A piezoelectric crystal resonates at the frequency at which the wavelength is equal to the thickness of the crystal.
FALSE.
Crystal thickness is HALF WAVELENGTH
or rephrased Wavelength is DOUBLE Crystal thickness
Ultrasound is converted to thermal energy as it propagates through tissue.
True
Fluid absorbs ultrasound to a greater degree than soft tissue.
FALSE. Fluid attenuates ultrasound less than soft tissue, hence post cystic enhancement.
Increased beam frequency decreases tissue absorption.
False
High frequency ultrasound is less penetrative than low frequency ultrasound.
True.
Ultrasound is generated and detected by thin piezoelectric discs, commonly made of lead zirconate titanate (PZT).
TRUE PZT = P is lead Z is zirconate T = Titanate
Transducer thickness is chosen to guarantee resonance at the required frequency.
True. Resonance of the crystal is dependent on the thickness and not the diameter:
A backing layer is included to ensure rapid damping of the transducer vibration.
True
An impedance matching layer is incorporated to achieve maximum energy transfer in and out of the patient.
True
The impedance matching layer results in a longer pulse and therefore has an adverse effect on pulse damping.
FALSE.
It is 1/4 wavelength thick to achieve this impedance matching
The matching layer does not extend pulse duration, but rather improves energy transfer and reduces reflection at the skin interface.
Pulse damping is determined by the Q-value of the transducer—a lower Q-value means better damping and shorter pulse duration.
The piezoelectric effect is when an electric potential is produced when a crystal undergoes a mechanical distortion.
True
The resonance frequency of the transducer crystal is dependent on the crystal diameter and not on its thickness.
Resonance of the crystal is dependent on the thickness and not the diameter:
Scatter in all directions occurs when the imaged structure has dimensions smaller than a wavelength of the ultrasound beam
True.
Scatter allows small structures to be visualized as some scatter will reach the transducer.
True.
Aliasing is a pulsed Doppler artefact.
True.
High Quality (Q) transducers are more efficient transmitters.
True: Quality (Q) = Energy lost per cycle / energy stored per cycle.
High Q-value transducers have low damping, meaning they continue to ring for a longer duration after excitation. This makes them more efficient transmitters of ultrasound energy because less energy is lost in damping .
Key Points:
* High Q-value → Less damping, longer pulse duration, more efficient energy transfer.
* Low Q-value → More damping, shorter pulse duration, better axial resolution.
Low Q transducers are more efficient receivers.
True.
Low Q-value → More damping, shorter pulse duration, better axial resolution.
A heavily damped transducer has a low Q factor.
True.
Low Q-value → More damping, shorter pulse duration, better axial resolution.
A lightly damped transducer has a high Q factor.
High Q-value → Less damping, longer pulse duration, more efficient energy transfer
The thicker the piezoelectric crystal the higher the resonance frequency.
False: A thicker crystal has a lower resonance frequency and a longer wavelength than a thinner crystal.
Acoustic impedance is the product of density and frequency.
False: Acoustic impedance = density x velocity of sound
dB is the unit of acoustic impedance.
False: The decibel (dB) is a logarithmic unit used to compare one intensity with a reference intensity.
A mirror image artefact commonly occurs at the diaphragm.
True
Ultrasound travels faster in soft tissue than bone.
True 1540m/s in soft tissue
4080 m/s in bone
330 m/s in air
Acoustic impedance is measured in milligrams per metre per second.
Kilogram per metre square per second.
E. Echoes from A-mode scans are displayed as a series of dots.
FALSE.
Echoes from A-mode are displayed as spikes and in B-mode are displayed as a series of dots.
In A-mode (Amplitude mode) ultrasound, the returning echoes are displayed as spikes on a 1D graph, not as a series of dots. The amplitude of each spike represents the strength of the echo from different tissue interfaces along the ultrasound beam path
A-mode scans can be used to measure the diameter of the eye.
True
Scatter contributes towards attenuation.
True: Attenuation is made up of absorption and scatter.
Ultrasound is attenuated exponentially with depth.
TRUE.
Attenuation of ultrasound is measured in kilograms per square metre per second.
FALSE. That’s acoustic impedance, Z.
Attenuation of US is measured in decibels per centimetre
Cavitation is a resonance phenomenon.
True.
Attenuation in ultrasound: Consists of absorption, reflection, and scatter.
True.
Attenuation is the loss of ultrasound energy as it travels through tissue.
The three main contributors to attenuation are:
* Absorption (conversion of sound energy into heat)
* Reflection (sound waves bouncing off interfaces)
* Scatter (redirection of sound waves by small structures)
Attenuation is halved when the path length is doubled.
Attenuation increases linearly with distance:
Total attenuation = attenuation coefficient x path length
Absorption is the conversion of sound to heat.
Absorption is the primary cause of attenuation and occurs when ultrasound energy is converted into heat within tissues .
A continuous alternating voltage applied to a transducer produces pulsed ultrasound.
False: A continuous alternating voltage applied to a transducer produces continuous ultrasound.
Frequency increases as the thickness of the transducer increases.
False: Frequency decreases as the thickness of the transducer increases.
Frequency bandwidth increases with decreasing pulse length.
True
Regarding ultrasound beam characteristics: The near field (Fresnel zone) diverges.
FALSE.
The near field (Fresnel zone) does not diverge; instead, it remains relatively parallel and well-defined. The ultrasound beam only begins to diverge in the far field (Fraunhofer zone)
The far field (Fraunhofer zone) extends a distance proportional to the square of the diameter of the transducer.
FALSE.
Near field = FRESNER = Diameter squared / 4 x wavelength
Side lobes are caused by radial (non-thickness) mode vibration of the transducer disc.
True
Side lobes may cause image artefacts.
True
Increasing the frequency or the diameter of the transducer increases the length of the near zone and decreases the divergence of the far zone.
TRUE.
- Near field length increases with frequency (f) → Higher frequency means longer near field.
- Near field length increases with transducer diameter (D²) → Larger diameter transducers provide a longer near field and better beam collimation.
- Near field length is inversely proportional to the speed of sound (c), which is constant in soft tissue (~1540 m/s).
Axial resolution is the ability of the ultrasound beam to separate two interfaces along the axis of the ultrasound beam.
TRUE
Azimuthal (lateral) resolution is the ability of ultrasound beam to separate two structures side by side at the same depth.
TRUE
Axial resolution is generally better than lateral resolution.,
True
- Axial resolution is better than lateral resolution because:
* It is dependent on shorter pulse length.
* Higher frequency ultrasound improves axial resolution by reducing wavelength. - Lateral resolution is limited by beam width, which varies with depth.
* To resolve two structures laterally, the beam must be narrower than the space between the objects.
* Beam focusing improves lateral resolution, but it is still generally worse than axial resolution. - Axial resolution is always superior to lateral resolutio
In the axial plane, two interfaces will be differentiated if the distance between them is less than half of the spatial pulse length.
FALSE.
The best axial resolution achievable is half of the spatial pulse length.
Interfaces must be further apart to be resolvable.
Resolution in the near field improves with focusing and a larger diameter transducer.
FALSE.
Larger diameter transducers extend the near field but can widen the beam, worsening lateral resolution in the near field.
Smaller diameter transducers produce a naturally narrower beam in the near field, leading to better lateral resolution at shallower depths.
Mechanical or electronic focusing narrows the beam width, improving lateral resolution in the near field.
Lateral resolution: It is equal to the beam diameter.
TRUE.
Lateral resolution is determined by beam width, which depends on transducer focusing and beam divergence.
It is approximately equal to the beam diameter at the focal poin
Increasing frequency improves lateral resolution for a given transducer diameter.
TRUE.
Lateral resolution improves with higher frequency because a higher frequency results in a narrower beam width.
Lateral resolution does not vary with distance from the transducer.
FALSE.
Lateral resolution worsens with increasing depth due to beam divergence in the far field.
* It is best at the focal zone and degrades beyond it
A small transducer improves lateral resolution for any given distance.
FALSE.
In the Near Field:
* A smaller transducer diameter produces a narrower beam in the near field, leading to better lateral resolution at shallow depths.
* However, it also shortens the near field length, meaning the beam starts diverging sooner, worsening lateral resolution at deeper depths.
In the Far Field:
* A smaller transducer results in greater beam divergence, worsening lateral resolution as depth increases.
* A larger transducer diameter creates a longer near field and maintains a narrower beam width at greater depths, improving lateral resolution in the far field.
Lateral resolution is determined by damping.
False: Lateral resolution is determined by frequency, focusing, transducer diameter and distance from the transducer:
In ultrasound a phased array can vary: Direction of the beam
In ultrasound a phased array can vary: Direction of the beam
In ultrasound a phased array can vary: Focal length
True. Bigger U, shorter depth
In ultrasound a phased array can vary: The pulse repetition frequency.
True.
Phased arrays adjust PRF dynamically based on depth and beam steering, particularly in Doppler imaging.
In ultrasound a phased array can vary: The axial resolution.
True: Axial resolution depends on pulse length which can be altered by changing the transmit frequency.
In ultrasound a phased array can vary: The lateral resolution.
True: Lateral resolution depends on beam focusing which is varied by altering delay lines.
A-mode scans: B. A-mode scans are inaccurate in measuring the amplitude of echoes.
FALSE.
A-mode is actually highly accurate in measuring echo amplitude, which is why it is still used in some applications like ophthalmology.
The amplitude of returning echoes is directly displayed as spike height, making it reliable for intensity measurement
A-mode scans: Amplitudes of echoes are presented as vertical deflections on the screen.
True.
The distance between targets cannot be measured with A-mode scans.
A-mode can measure distances between interfaces based on the time delay of returning echoes.
A-mode scans: Dedicated A-mode equipment is still frequently used
False: Dedicated A-mode equipment is rarely manufactured but it is used as an additional feature on B-scan equipment.
A-mode scans: Can measure foetal biparietal diameter.
A-mode can be used to measure the biparietal diameter (BPD) of the fetus, though B-mode is now preferred.
It was one of the earliest techniques for fetal measurements
B-mode scans: A. The beam axis (scan line) is swept through the area of interest to define a scan plane.
True
B-mode scans: BThe echoes from all scan lines are displayed as a two dimensional image of the scan plane.
True
B-mode scans: The amplitude of the echo is inversely proportional to the brightness of the corresponding point on the display.
False: The amplitude of the echo is proportional to the brightness of the corresponding point on the display.
B-mode scans: Multiple pulses are required per line to build up a single image.
False: Only a single pulse is required but multiple pulses may be used if, for example, multiple focal zones are being used.
B-mode scans: E. Can be used to produce a cross-sectional image of the eye and the orbit.
True.
Time-gain compensation is used to: Improve lateral resolution.
False.
Lateral resolution is determined by beam width, focusing, and transducer characteristics, not by TGC
TGC: Compensate for the difference in time between the front and back of a signal.
False.
TGC is not related to the timing of signals, but rather to compensating for attenuation over depth
TGC: Compensate for the difference in attenuation between different tissues.
True
Compensate for the effect of attenuation with distance travelled within a medium.
True.
TGC is used to Obtain similar intensity signals from all similar boundaries.
True. TGC helps in normalizing echo intensities so that boundaries at different depths produce similar signal amplitudes.
M-mode scans
Display the position of reflecting surfaces along a single scan line versus time.
True
M-mode scans
The echo brightness indicates the echo amplitude.
True
M-mode scans
The vertical co-ordinate represents time whilst the horizontal co-ordinate represents depth.
False. Opposite
M-mode sca
Each transmission-reception sequence is summated with the previous M-mode line.
True: Increasing intensity will increase echo amplitude at depth.
M-mode scans are primarily used in cardiac imaging.
True.
To see deeper structures on US:
Reducing the frequency to lessen the effect of absorption.
True
To see deeper structures more readily on US:
Increasing the brightness of the display to show the weaker echoes.
False: Increasing the brightness of the display will also increase the brightness of the noise, hence it will not improve signal to noise ratio.
To see deeper structures on US:
Increase the ultrasound intensity.
True
US: Contrast agents improve image quality and information by increasing reflections from tissue containing the agents.
True
Microbubbles used as ultrasound contrast agents (UCAs) typically range in size from 1 to 10 micrometres (µm) in diameter. This size allows them to remain within the bloodstream without passing through the capillary walls, making them useful for contrast-enhanced ultrasound imaging.
Microbubbles can be destroyed by low intensity ultrasound.
False. High intensity.
Tissue harmonic imaging can increase reverberation artefacts.
False. Tends to reduce it.
Tissue harmonic imaging can decrease scatter and distortion from fatty tissues, and hence leads to an improvement in image contrast.
True.
Doppler effect: The calculation of the change in frequency involves the sine of the angle between the incident and reflected direction.
False: It involves the COSINE of the angle between these directions.
Doppler shift frequency is directly proportional to:
The angle of the ultrasound (US) beam.
FALSE. COSINE ANGLE.
Doppler shift frequency is directly proportional to:
The speed of the target material.
IF it means speed of the target MATERIAL as in tissue = c = then NO INVERSELY proportional
If speed of the TARGET e.g. RBC = v = then YES directly proportional
Doppler shift frequency is directly proportional to: Beam intensity
Object size
BOTH FALSE. Irrelevant
Doppler shift frequency is directly proportional to: The frequency of the US beam.
TRUE.
f0 = transmitted ultrasound frequency
The maximum Doppler shift frequency that can be detected is half the PRF.
True.
This is known as the Nyquist limit, which states that the maximum detectable Doppler shift is half the Pulse Repetition Frequency (PRF):
f Nyquist = PRF / 2
Depth assessment requires gating.
True.
Pulsed Doppler uses a range gate to select echoes from a specific depth by timing their arrival.
This allows precise depth localization of blood flow velocity.
Doppler: The change in frequency is greatest with the beam perpendicular to the direction of flow.
FALSE.
Doppler shift is maximum when the ultrasound beam is parallel (0° or 180°) to flow and zero when perpendicular (90°).
Doppler: Sound velocity is increased by increased source motion.
False: Sound velocity is dependent on density and compressibility, not on how fast a source is moving.
Motion of the source does not change the speed of sound in tissue (1540 m/s). It only affects the Doppler shift frequency.
The intensity of the back scattered signal is independent of the beam frequency.
The intensity of the backscattered signal increases with higher ultrasound frequency due to greater interaction with small particles (e.g., red blood cells).
Doppler: It produces a change in frequency which is inversely proportional to the velocity of sound in the medium.
velocity of sound in the medium = c
Doppler: It requires a higher frequency than would be used for imaging.
True
The Doppler shift frequency is equal to 1 over the transmitted frequency.
FALSE.
Velocity of blood flow is most accurately measured when the ultrasound beam is less than 60° to the direction of blood flow.
True: This is because the velocity is related to the cosine of the angle.
At a 60-degree angle, a 5-degree error in angle measurement gives an error of 15% in the cosine of the angle.
At an 80-degree angle, the same 5-degree error in angle measurement would give an error of 50% in the cosine of the angle, resulting in large errors in velocity estimation.
Spectral analysis of pulsed wave Doppler signals is usually accomplished using an autocorrelation technique.
FALSE.
Fast Fourier Transform (FFT) is the technique used for spectral analysis in pulsed wave Doppler.
Autocorrelation is used for color Doppler imaging, not pulsed wave Doppler.
There is a maximum velocity which can be detected with DOPPLER.
False: There is no limit to the velocity that can be detected using continuous wave Doppler, a limit only applies when using pulsed Doppler.
Autocorrelation Technique in Doppler Ultrasound
Definition:
Autocorrelation is a mathematical signal-processing technique used in colour Doppler ultrasound to rapidly estimate the mean Doppler shift frequency and direction of blood flow at multiple points within a vessel.
Unlike Fast Fourier Transform (FFT), which is used in pulsed-wave spectral Doppler, autocorrelation is optimized for real-time colour flow imaging, where speed is prioritized over precision.
Doppler: PRF can be a limiting factor in the detection of signals from deep vessels.
True: Enough time must be allowed for echoes to return from deep structures before the next pulse can be sent out.
Doppler signals should preferably be acquired at angles between 30 and 60 degrees.
True.
Ideal range: 30° to 60°. At higher angles (>60°), small errors in angle estimation cause large velocity errors.
Pulsed Doppler: The Nyquist limit is determined by the PRF.
True Nyquist limit = PRF / 2
Pulsed Doppler: There is a maximum velocity that can de detected.
True.
Max velocity in pulsed doppler
Pulsed Doppler: Using high PRF avoids range ambiguity.
False: Using a high PRF may create range ambiguity as echoes generated from deeper structures will arrive at the transducer shortly after the next pulse is transmitted and will be misregistered as coming from superficial structures.
Pulsed Doppler: Typical Doppler shift frequencies produced diagnostically are inaudible.
False: Typical Doppler shift frequencies produced are within audible range hence the use of loudspeakers as a primary output device.
Duplex scanning is a combination of Doppler measurement with a real time B-scan image.
TRUE
US: A lower PRF is required to visualize deeper vessels.
True: More time must be allowed for echoes from deep structures to return to the transducer and therefore the number of pulses per second (PRF) has to be decreased.
Power Doppler differentiates between areas with flow and areas devoid of flow.
True
Differences between colour and power doppler
Differences between ALL the dopplers
Power Doppler is not subject to aliasing.
True.
Power Doppler is not subject to aliasing because it does not rely on frequency shifts but rather signal amplitude. However, it does not provide velocity or direction information, making it less useful for certain vascular assessments.
Tissue heating occurs in the therapeutic US range.
True
Acoustic streaming results from ultrasound energy being absorbed by a medium and has the potential to cause cellular damage.
False.
Acoustic streaming is a nonthermal bioeffect caused by ultrasound-induced fluid motion.
It does not cause direct cellular damage but may influence biological processes.
Cavitation (not acoustic streaming) is more likely to cause cellular damage.
Biological effects of ultrasound:
Transient (unstable) cavitation occurs when changes in pressure cause microbubbles to expand and contract until they implode with high temperature rises causing profound cellular damage.
TRUE.
Transient cavitation occurs at high acoustic pressures.
Microbubbles expand and collapse violently, generating:
- Localized high temperatures (~5000 K)
- High-pressure shock waves
This can cause severe cellular damage, unlike stable cavitation, which is less harmful.
Biological effects of ultrasound:
Transient cavitation most commonly occurs at low pressure and high frequencies.
False. Transient cavitation occurs at HIGH PRESSURE and LOW FREQUENCIES.
At low frequencies, bubbles grow larger before collapsing, increasing damage.
At high frequencies, bubble oscillations are more stable, reducing transient cavitation.
Biological effects of ultrasound:
If mechanical index (Ml) reaches 0.1 there is a possibility of minor damage to neonatal lung or intestine and exposure time should be limited.
FALSE.
British Medical Ultrasound Society (BMUS) guidelines, an MI greater than 0.3 may cause minor damage to neonatal lung or intestinal tissues. Therefore, exposure time should be minimized in such cases.
gas-containing structures (such as the bowel and lung) have an increased risk of cavitation when exposed to ultrasound
The highest intensity that can be measured in an ultrasound beam is the spatial peak temporal average intensity (ISPTA).
FALSE.
I SPTP – Spatial Peak Temporal Peak Intensity = Maximuminstantaneousintensityatthespatialpeak
NOT to be confused with
Spatial Peak Pulse Average Intensity
I SPPA = [Totalacousticenergyinonepulse] / [pulse duration]
Spatial Peak Temporal Average Intensity (ISPTA)
I SPTA = [Totalacousticenergydeliveredoveralongperiod] / [Total measurement in time including gaps between pulses]
MI thresholds for Ultrasound
For general diagnostic ultrasound, the MI should be less than 0.7.
For foetal and neonatal imaging, the MI should be less than 0.5.
MI values greater than 0.7 should never be used with ultrasound contrast agents due to increased cavitation risk
The intensity of an ultrasound beam in water is greatest in the focal region.
True. Narrowest part of beam
Intensity of diagnostic ultrasound:
The time-averaged intensity must never exceed 100mW/cm2.
The BMUS guidelines state that the recommended safe time-averaged intensity limit is <100mW/cm², but this is not a strict upper limit in all cases
ISPTA is generally highest in pulsed Doppler mode.
True.
ISPTA (Spatial Peak Temporal Average Intensity) represents the average intensity over time at the most intense location in the ultrasound beam.
The duty cycle (percentage of time the transducer is actively transmitting) is much higher in pulsed Doppler than in B-mode.
To estimate intensity in tissue, the acoustic pressure inUSwater is measured using a hydrophone and a derating factor is applied to allow for the effects of attenuation.
True: An attenuation rate of 0.3dB/cm/MHz is assumed to estimate the intensity in tissue.
US thermal index (TI) gives an indication of the temperature rise in tissue.
True. The Thermal Index (TI) measures the ability of ultrasound to heat local tissue
TI is the ratio of the in situ acoustic power to the power required to increase the tissue temperature by 10°C.
FALSE.
TI =
[Poweremitted]
/
[Power to increase tissue by 1 degrees C]
Thermal Index safety table
Mechanical Index safety table
TIB refers to the thermal index to be used if bone is situated at the surface (i.e. transcranial applications).
FALSE.
TIB (Bone TI) - Used when bone is near the FOCAL REGION (e.g., second and third trimester fetal ultrasound).
TIC (Cranial TI) - Used when bone is at the surface (e.g., transcranial applications).
The mechanical index (Ml) is defined as the derated peak rarefactional pressure divided by the square root of frequency.
TRUE
Peak rarefactional pressure refers to the negative pressure in the ultrasound wave that contributes to bubble formation (cavitation).
“Derated” pressure means the actual pressure in tissue, adjusted for attenuation effects in soft tissue.
The square root of frequency is used in the denominator because higher frequencies reduce the risk of cavitation.
This formula provides a measure of the likelihood of cavitation effects in tissue
The mechanical index (Ml) is a guide to the likelihood to cavitation.
True.
Thermal index (TI) in ultrasound:
ls inversely proportional to the power emitted.
FALSE. DIRECTLY PROPORTIONAL
Thermal index (TI) in ultrasound:
US:A TI of less than 0.5 is considered safe.
TRUE.
BMUS guidelines state that a TI < 0.5 is below the threshold for any significant biological effects
Thermal index (TI) in ultrasound:
The scanning time of an embryo or foetus should be reduced when the thermal index is greater than 1.
TRUE.
BMUS guidelines recommend limiting exposure time when TI > 1, particularly in fetal imaging.
Thermal index (TI) in ultrasound:
Particular care should be taken to reduce output and minimize the exposure time of an embryo or foetus when scanning a febrile patient.
TRUE.
A febrile patient already has an elevated baseline temperature, making additional heating from ultrasound more significant. BMUS recommends extra caution in such cases
Thermal index (TI) in ultrasound:
Real time values of Tl and Ml must always be displayed on the scanner.
FALSE.
MI must be displayed when it exceeds 1.0 in B-mode imaging
TI is only required to be displayed when it exceeds 0.4 in Doppler mode
US Safety: Tissue heating damaging foetal dividing cells during the first 8 weeks of gestation is of particular concern.
True
Tissue heating can be particularly harmful to rapidly dividing foetal cells in the first 8 weeks of gestation.
This is a critical period of organogenesis, and temperature elevations can increase the risk of developmental abnormalities.
Tissue heating in ultrasound:
Temperature increase to the foetus in excess of 1.5°C is potentially hazardous and exposure time should be limited.
TRUE.
The BMUS guidelines highlight that a temperature rise greater than 1.5°C above baseline can be potentially hazardous, particularly in foetal tissues.
Exposure time should be minimised, especially in early pregnancy, to reduce thermal risk.
Tissue heating in ultrasound:
B-mode causes a higher temperature rise than pulsed Doppler mode for the same given time.
TRUE.
Pulsed Doppler mode produces a higher temperature rise than B-mode.
This is due to its higher intensity and longer dwell time in a focused region, increasing thermal effects.
Pulsed Doppler mode also has greater heating potential due to the high pulse repetition frequencies and the pulse lengths used.
Tissue heating in ultrasound:
The temperature rise in soft tissue is greater than bone.
FALSE.
Bone is associated with the highest temperature rise secondary to its high absorption coefficient.
bone absorbs more ultrasound energy than soft tissue, leading to a greater temperature rise in bone. This is particularly relevant in later pregnancy when ossified foetal bones can experience localised heating.
Tissue heating in ultrasound:
Pre-existing temperature elevation and the heat from the probe are additives to tissue heating.
The BMUS safety guidelines acknowledge that pre-existing temperature elevation (e.g., maternal fever) and probe-generated heat contribute additively to tissue heating. This cumulative effect should be considered when performing obstetric ultrasound scans.
The gyromagnetic ratio of a hydrogen (1H) atom is 42.57 MHz T-1.
TRUE.
Spin-lattice relaxation describes the decay of transverse magnetization.
False: This is spin-spin relaxation.
The time constant ofT2 is always shorter than the time constant of T1 for the same tissue.
True
Only hydrogen nuclei are said to be MR active.
False: Nuclei with an odd number of protons are said to be MR active.
These include Hydrogen-1, Carbon-13, Fluorine-19, Phosphorous-31, Nitrogen-15, Oxygen-17, Sodium-23, etc.
Faraday’s law of induction states that the change in magnetic flux through a closed circuit induces an electromotive force (electric current) in the circuit.
True: This electromagnetic induction is a basic principle of MRI. This principle is also applied to various other devices such as graphics tablets, loudspeakers, and electric guitar pickups.
The strength of the magnetic field (B) is measured in gauss (G).
True: The strength of the magnetic field (B) is measured in both Gauss and Tesla.
Tesla is the SI unit for magnetic flux density.
An MR active nucleus spins at its own precessional frequency.
False: They only precess when under the influence of an external magnetic field.
The temperature of the sample does not affect the magnetic moments of hydrogen atoms.
True.
The magnetic moment of hydrogen nuclei (protons) arises from their intrinsic spin.
While the intrinsic magnetic moment itself is not temperature-dependent, the net magnetization (M₀) of a sample in an external magnetic field is affected by temperature.
According to Boltzmann distribution, at higher temperatures, more hydrogen nuclei are in an excited state (higher energy level), reducing the net alignment with the external magnetic field.
The equilibrium longitudinal magnetization (M₀) is proportional to 1/𝑇 (temperature-dependent), meaning that as temperature increases, the net magnetization decreases.
By applying an RF 90 to the B0:
The net magnetization vector rotates around the transverse plane inducing signal across the receiver coil by inducing a voltage within it.
TRUE.
Once in the transverse plane, M₀ precesses at the Larmor frequency, generating an electromagnetic signal that is detected by the receiver coil via Faraday’s Law of Induction.
By applying an RF 90 to the B0:
Nuclei are flipped onto their sides in the transverse plane.
FALSE.
The physical nuclei do not move or “flip” in space. Instead, their magnetic moments (or the net magnetization vector) change orientation relative to the external magnetic field (B₀).
A 90-degree RF pulse rotates the net magnetization vector (M₀) from the longitudinal (z-axis) to the transverse plane (xy-plane).
By applying an RF 90 to the B0:
Some nuclei gain enough energy to join the high energy population.
TRUE.
Protons transition from the low-energy state (aligned with B₀) to the high-energy state (anti-parallel to B₀), in accordance with the Boltzmann distribution.
By applying an RF 90 to the B0:
The magnetic moments of the nuclei move out of phase of each other.
FALSE. RF pulse actually synchronizes the phase of the spins, creating phase coherence in the transverse plane.
Water has high molecular motion (inherent energy) and therefore decays faster than fat.
False: Water decays slower than fat because it has faster molecular motion (inherent energy) than fat.
The faster the molecular motion the more difficult it is for a substance to release energy to its surroundings.
Water molecules exhibit higher molecular motion due to weaker intermolecular forces.
T1 IS LONG FOR WATER
Shim coils are used to combat inhomogeneities caused by the external magnetic field.
True
ecay is due to dephasing caused by inhomogeneities of the external magnetic field.
False: this is T2*.T2 dephasing is caused by spin-spin energy transfer.
Fat has low molecular motion (inherent energy) and therefore recovers quicker than water.
True.
T1 relaxation (spin-lattice relaxation) is faster in fat than in water, meaning that fat recovers its longitudinal magnetization more quickly.
This is why fat appears bright on T1-weighted images, while water appears darker due to its longer T1 recovery time.
By applying an RF 90 to the B0:
There is energy absorption.
TRUE.
When an RF pulse is applied at the Larmor frequency, protons absorb energy from the electromagnetic field, causing transitions between energy states.
This is a fundamental principle of resonance in MRI.
T1 recovery time is defined as the time it takes for 100% of the longitudinal magnetization to recover.
False: T1 is defined as the time it takes for 63% of the longitudinal magnetization to recover.
T1 GOES FIRST so takes 2/3rd share
Using a long TR (time to repetition) allows saturation to occur which enhances contrast.
FALSE.
Saturation effects in MRI refer to a condition where the longitudinal magnetization (M₀) does not fully recover before the next RF pulse is applied. This affects signal intensity and contrast in different MRI sequences.
Long TR actually minimizes saturation effects, allowing full T1 recovery before the next RF pulse.
Short TR leads to saturation effects, meaning there is incomplete recovery of longitudinal magnetization before the next RF pulse.
Water has a short T1 recovery time.
FALSE.
Water has a long T1 recovery time, meaning it takes longer to return to its equilibrium longitudinal magnetization.
This is why water appears dark on T1-weighted images.
Fat has a short T1 recovery time.
True.
This is why fat appears bright on T1-weighted images, as it recovers quickly between RF pulses and emits stronger signals.
In a proton density (PD) image, long TR is used to allow for saturation to occur to enhance contrast
False: In PD weighted images, a long TR is used to allow full recovery of the longitudinal components of fat and water.
There is no contrast difference and any differences seen are inherent to the proton density differences of each tissue. No saturation occurs.
T1 recovery of fat is shorter than that of water.
True.
Fat has a shorter T1 recovery time than water, meaning it returns to equilibrium (longitudinal magnetization) faster.
T2 decay of fat is shorter than that of water.
True: Fat has a short T1 recovery AND T2 decay compared to water.
T2 relaxation (spin-spin dephasing) is influenced by molecular interactions, and fat has stronger dipole-dipole interactions, leading to a shorter T2 time.
Water has a longer T2 decay time, meaning it retains transverse magnetization longer and appears bright on T2-weighted images.
Tissues with low proton density such as air alwappear as a low signal on an MR image.
True
T1 recovery time is defined as the time it takes for 63% of the longitudinal magnetization to recover.
True.
T1 recovery time is the time required for longitudinal magnetization to recover to 63% of its equilibrium value.
T2 decay time is defined as the time it takes for 63% of transverse magnetization to be lost due to dephasing.
True.
T2 decay time is the time it takes for transverse magnetization to decay to 37% (or 1/𝑒 of its original value, which means that 63% of the signal is lost.
RegardingT1-weighted images
Fat appears as a high signal.
Fat has a short T1 recovery time, meaning it quickly regains longitudinal magnetization and emits a strong signal when the next RF pulse is applied.
This results in fat appearing bright (high signal) on T1-weighted images.
Regarding T1-weighted images:
Slow flowing blood appears as a low signal.
FALSE.
In spin-echo sequences, slow-flowing blood may exhibit high signal because it remains in the imaging plane long enough to experience multiple RF excitations and recover longitudinal magnetization, leading to a bright appearance.
Fast-flowing blood, on the other hand, often appears dark due to flow voids (it moves out of the imaging plane before it can be fully excited and contribute to the MR signal).
RegardingT1-weighted images
Water appears as a low signal.
Water has a long T1 recovery time, meaning it takes longer to return to equilibrium longitudinal magnetization.
Because of this, water appears dark (low signal) on T1-weighted images.
Regarding T1-weighted images
Typical time to echo (TE) is 80 ms.
T1-weighted images use a short TE, typically around 10-30 ms.
A TE of 80 ms is more typical for T2-weighted imaging, not T1-weighted imaging.
Regarding T1-weighted images
Typical TR is 300-600 ms
TRUE.
T1-weighted images use a short TR, typically in the range of 300-600 ms, to allow for partial T1 recovery while still emphasizing T1 contrast.
A short TR ensures that tissues with shorter T1 (such as fat) appear bright, while tissues with longer T1 (such as water) remain darker.
T2-weighted images using spin echo:
Haemangiomas appear as high signal.
True
Haemangiomas (vascular lesions) often appear as high signal on T2-weighted images because they contain slow-flowing blood and fluid-filled spaces, both of which have long T2 relaxation times.
T2-weighted images using spin echo:
Cerebrospinal fluid (CSF) appears as high signal.
CSF has a long T2 relaxation time, meaning it retains transverse magnetization for a longer duration.
T2-weighted imaging highlights fluids, so CSF appears bright (high signal) due to its long T2.
T2-weighted images using spin echo:
Lipomas appear as high signal.
False: Lipomas consist mostly of fat and therefore appear as a low signal because they lose most of their transverse coherence during a long TE.
However, using fast spin echo (FSE), fat remains a high signal secondary to the J-coupling phenomenon.
T2-weighted images using spin echo:
Most pathologies are high signal on T2-weighted image.
True.
T2-weighted imaging is highly sensitive to pathology because most pathological tissues have increased water content (e.g., inflammation, edema, tumors).
Since water has a long T2 relaxation time, most pathologies appear bright (high signal) on T2-weighted images.
T2-weighted images using spin echo:
Typical TR is 2000ms.
True.
A typical TE for a T2-weighted spin-echo sequence is around 80–120 ms.
Regarding proton density(PD)-images
Cortical bone has very low proton density, meaning it contains very few mobile hydrogen protons to generate a signal.
As a result, cortical bone appears as a low signal (dark) on PD-weighted images.
Regarding proton density(PD)-images
CSF appears as a high signal
CSF has a high proton density because it consists mostly of free water.
Regarding proton density(PD)-images
T1 effect is reduced by selecting short TE.
False: T1 effect is reduced by selecting long TR.
Regarding proton density(PD)-images
T2 effect is reduced by selecting long TR
False: T2 effect is reduced by selecting short TE.
Regarding proton density(PD)-images
Typically uses short TE and long TR.
True.
Typical relaxation times of tissues in a field of 1T:
T2 of fat is typically 80ms.
True.
In 1 Tesla:
Fat:
T2: Approximately 60–80 ms
T1: Approximately 240–250 ms
Typical relaxation times of tissues in a field of 1T:
T1 of CSF is typically 150 ms.
FALSE.
CSF has a very long T1 relaxation time.
At 1T, the T1 of CSF is approximately 2000–2500 ms, depending on temperature and exact conditions.
Typical relaxation times of tissues in a field of 1T:
T1 of water is typically 3000ms.
True.
Water has a long T1 (~3000 ms at 1T).
Typical relaxation times of tissues in a field of 1T:
T2 of CSF is typically 150ms.
True.
T2 of CSF is ~140-180 ms at 1T.
Typical relaxation times of tissues in a field of 1T:
T2 of water is typically 3000ms.
True.
T2 of water is typically 3000ms.
The following are contraindications in MRI examinations:
Prosthetic heart valves.
False.
Most modern prosthetic heart valves are MRI-safe, but older ferromagnetic models may pose a risk. Evaluation is case-dependent.
The following are contraindications in MRI examinations:
Cochlear implants.
True.
Cochlear implants contain metallic components that can be hazardous in an MRI scanner, making them a strong contraindication.
The following are contraindications in MRI examinations:
Cardiac pacemakers.
True.
Pacemakers are a well-known MRI contraindication, as the strong magnetic field can interfere with their function. Newer MRI-conditional models exist but require specific protocols.
The following are contraindications in MRI examinations:
Intra-ocular ferrous foreign body.
TRUE.
Metallic (ferrous) foreign bodies in the eye pose a serious risk, as MRI can cause them to move, leading to severe injury.
The following are contraindications in MRI examinations:
Orthopaedic implants.
False.
Most orthopaedic implants show no deflection within the main magnetic fields. Although some theoretical risk of heating can occur secondary to induced currents, this is thought to be minimal.
adient echo uses a fixed flip angle of 90 degrees.
False.
Gradient echo sequences use a variable flip angle, which is typically much lower than 90 degrees to allow for faster imaging.
Gradient echo is a fast sequence when compared with spin echo.
True.
Gradient echo sequences are designed to be faster than spin echo by using shorter TR and flip angles, omitting the 180-degree rephasing pulse.
Gradient echo produces true T2 weighted images
FALSE.
Gradient echo sequences do not produce true T2-weighted images; they are T2-weighted because they do not compensate for field inhomogeneities.*
In fast or turbo spin echo sequences, TR is shorter than in conventional spin echo.
FALSE.
In turbo spin echo (TSE), TR is often lengthened to allow multiple echoes to be collected per TR cycle, improving signal-to-noise ratio.
Regarding spin echo sequences:
In T2-weighted scans on fast or turbo spin echo sequences, fat appears as high signal.
TRUE.
This is due to a succession of 180 degree RF pulses which reduce the spin-spin interactions in fat thereby increasing its T2 decay time (also known as J coupling).
Due to multiple 180-degree pulses in TSE, J-coupling effects cause fat to appear bright on T2-weighted turbo spin echo images.
Regarding spin echo sequences:
In T2 weighted scans on fast or turbo spin echo sequences, water appears as high signal.
True.
Water retains its high signal intensity on T2-weighted turbo spin echo sequences because it has a long T2 relaxation time.
Regarding spin echo sequences:
In inversion recovery, the sequence starts with a 180-degree inverting pulse.
TRUE.
In inversion recovery sequences, a 180-degree pulse is applied first to invert the longitudinal magnetization before the standard spin echo process begins.
Regarding inversion recovery sequences:
The TR is the time between successive 180 degrees inverting pulse.
FALSE.
I an inversion recovery sequence, the “TR” (repetition time) refers to the time between successive 90-degree excitation pulses.
NOT the 180-degree inverting pulses;
The key parameter for manipulating contrast in an inversion recovery sequence is the “TI” (inversion time), which is the time between the 180-degree inverting pulse and the following 90-degree excitation pulse.
Fluid-attenuated inversion recovery (FLAIR) uses a short time to inversion (TI).
FALSE.
FLAIR uses a long TI (~2000 ms) to null the signal from CSF. A short TI would not effectively suppress CSF.
CSF has a long T1
Regarding inversion recovery sequences:
Time to inversion (TI) is the time between successive 180 degrees pulse.
False: TI is the time between 180 degrees pulse and the 90 degree pulse.
Regarding inversion recovery sequences:
Time to inversion (TI) is used as a T1 contrast control.
True.
TI controls the degree of T1 contrast by determining how much longitudinal magnetization has recovered before the excitation pulse is applied. Aim is NET ZERO before the 90 flip to SUPPRESS.
FLAIR is used to null the signal from CSF.
FLAIR is specifically designed to suppress CSF signal, making it useful for detecting pathology in periventricular areas.
TR used in gradient echo is shorter than in spin echo.
True.
Gradient echo sequences use a much shorter TR than spin echo, allowing for faster imaging. This is because they do not require a 180-degree refocusing pulse.
Regarding gradient echo sequences:
T1 image uses a large flip angle (60-120 degrees).
True.
For T1-weighted gradient echo imaging, a large flip angle (typically 60-120 degrees) is used to enhance T1 contrast.
Regarding gradient echo sequences:
As in spin echo, TR controls T1 weighting.
True.
TR influences T1 weighting in both spin echo and gradient echo sequences. A short TR enhances T1 contrast, while a long TR reduces it.
Regarding gradient echo sequences:
Moving blood appears as a low signal.
FALSE.
In gradient echo sequences, moving blood often appears as a high signal due to flow-related enhancement (time-of-flight effect), unlike in spin echo where flow voids cause signal loss.
PD image uses a large flip angle (60-120 degrees).
False.
Proton density (PD) images use a small to intermediate flip angle (typically 30-50 degrees), not a large flip angle, to minimize both T1 and T2 effects
Regarding slice selection:
The Z gradient selects axial slices.
True. The Z gradient is applied to select axial slices because it alters the magnetic field along the Z-axis, allowing selection of slices in that plane.
Slice selection transmit bandwidth determines the slice thickness.
True.
The steeper the slice select gradient, the thicker the slice.
FALSE. THINNER FOR A GIVEN BANDWIDTH
During slice selection, increasing transmit bandwidth increases axial spatial resolution.
False: Increasing transmit bandwidth increases slice thickness, thereby decreasing axial spatial resolution.
The slice select gradient is also switched on during the 180 degrees pulse in spin echo sequences.
True. Otherwise your 90 and 180 flips will not be specific for your slice!
So that rephasing can be delivered specifically to the selected slice.
Regarding spatial encoding:
Phase encoding occurs during the 180 degrees rephasing pulse.
FALSE.
Phase encoding is applied AFTER slice selection but before frequency encoding, NOT during the 180-degree pulse.
IT can be before the 180 degrees rephasing pulse but it would need to be inverted if AFTER the 180.
Regarding spatial encoding:
The slope of the phase encoding gradient determines spatial resolution.
True: Steeper gradients produce greater phase shifts between 2 points and increase the phase matrix FOY, thus improving spatial resolution along the phase axis.
Regarding spatial encoding:
In standard orientation, the phase encoding gradient produces a gradient across the x-axis.
False: Across the y-axis.
Regarding spatial encoding:
In standard orientation, the frequency encoding gradient produces a gradient across the y-axis.
False: Across the x-axis.
Regarding spatial encoding:
Frequency encoding is applied during TE.
True
SNR in MRI increases with increasing field strength
SNR increases with increasing field strength (Bo) because it enhances magnetisation (Mo) and longitudinal magnetisation (Mz), leading to a stronger signal
SNR in MRI: It is not related to the positioning of the receiver coils.
SNR is strongly dependent on the positioning of receiver coils. Coils placed closer to the region of interest detect stronger signals with reduced noise
SNR in MRI: Increasing TE improves SNR
SNR decreases as TE increases because a longer TE allows more time for T2 decay, reducing transverse magnetisation (Mxy) before signal readout
SNR in MRI: Reducing the receiver bandwidth increases SNR.
True.
Reducing receiver bandwidth reduces noise, thereby increasing SNR. However, this comes at the expense of longer scan times#
Reducing receiver bandwidth reduces the proportion of noise sampled relative to the signal, therefore boosting SNR
SNR in MRI: It depends on flip angle.
TRUE.
SNR is influenced by flip angle. The optimal flip angle (Ernst angle) maximises signal intensity based on T1 relaxation
SNR in MRI: lncreasing TR increases signal.
True. This allows more longitudinal magnetisation to recover with time.
Increasing TR increases signal because it allows more longitudinal magnetisation (Mz) to recover between pulses. This effect is observed up to approximately TR = 5 T1
SNR in MRI: Using a contrast medium increases signal to noise ratio (SNR)
False.
Strictly speaking, using contrast increases contrast to noise ratio, and not SNR.
SNR in MRI:
By halving x,y FOV (field of view) (keeping slice thickness the same), the SNR is halved.
Halving the FOV results in a fourfold decrease in voxel size, leading to an SNR reduction by a factor of 4, not just halved
MRI: Increasing the number of signal averages (NSA/NEX) increases SNR.
True.
NSA (Number of Signal Averages) and NEX (Number of Excitations) are interchangeable terms in MRI.
MRI: Decreasing matrix size increases SNR
A smaller matrix increases the size of each voxel, allowing more signal per voxel, which improves SNR
MRI: Increasing FOV increases spatial resolution.
FALSE.
Increasing the Field of View (FOV) decreases spatial resolution because larger FOVs require larger voxels (keeping matrix size constant), which reduce detail.
Smaller FOV improves spatial resolution by reducing voxel size.
MRI: Increasing matrix size increases spatial resolution.
True.
A larger matrix size means more pixels, reducing voxel size and improving spatial resolution.
Example: A 512 × 512 matrix has better resolution than a 256 × 256 matrix, as each pixel represents a smaller portion of the image.
MRI: Increasing slice thickness decreases spatial resolution.
True.
Thicker slices reduce spatial resolution because they average signal over a larger volume, leading to partial volume effects.
MRI: Spatial resolution affected by number of frequency encoding steps
True.
More frequency encoding steps increase spatial resolution by providing finer sampling in the frequency direction.
Higher encoding steps help in creating sharper images with better detail.
A larger frequency matrix means smaller voxel sizes in the x axis, improving spatial resolution.
MRI SNRL It is improved by using small coils
True.
Using smaller coils improves spatial resolution because they detect signal from a smaller region, reducing noise and improving image quality.
MRI Scan time depends on:
A TR.
B. TE.
C. The number of frequency encoding steps.
D. The number of signal averages (NSA/NEX).
E. The number of slice encodings.
B and C are false
A. Scan time is directly proportional to TR because each repetition cycle (TR) must be completed before moving to the next phase encoding step.
B. TE does not directly affect scan time because it only determines when the signal is read during each TR cycle.
C. Frequency encoding is applied once per TR and does not influence scan time.
Phase encoding (not frequency encoding) affects scan time because it requires multiple repetitions.
D. Increasing NSA/NEX increases scan time linearly because it requires repeating the entire scan multiple times for noise averaging.
E. For 3D imaging, slice encoding requires additional phase encoding steps, increasing scan time.
In 2D imaging, scan time is usually independent of slice number because slices are acquired sequentially.
Spatial encoding gradients are used to control FOV.
True.
Field of View (FOV) is controlled by the spatial encoding gradients, particularly the phase and frequency encoding gradients.
A weaker gradient increases FOV, whereas a steeper gradient reduces FOV.
The steeper the frequency, and phase encoding gradients, the larger the FOV.
In the frequency encoding direction, all information is acquired during TE.
In the phase encoding direction, all information is acquired after a single gradient step.
Slice selection gradient is used to control thickness.
True.
The slice selection gradient determines slice thickness, as it defines the frequency range excited by the RF pulse.
Large slice selection bandwidth = THICKER slice
The steeper the frequency, and phase encoding gradients, the larger the FOV.
FALSE.
STEEPER GRADIENTS = SMALLER FOV
In the frequency encoding direction, all information is acquired during TE.
Frequency encoding occurs DURING SIGNAL READOUT at TE.
This is when the frequency encoding gradient is applied, and data is collected.
In the phase encoding direction, all information is acquired after a single gradient step.
FALSE.
Phase encoding requires multiple gradient steps, with each phase encoding step contributing one line of k-space.
Each TR cycle collects only one phase encoding step, meaning full image acquisition requires multiple TRs.
Chemical shift artefact: It occurs in the frequency encoding direction.
True.
Chemical shift artefact occurs along the frequency encoding direction because fat and water have different precessional frequencies, leading to spatial misregistration.
Chemical shift artefact: It can be remedied by using a stronger magnetic field.
False.
A stronger magnetic field actually exacerbates chemical shift artefact because the frequency difference between fat and water increases with field strength.
Chemical shift artefact: It is decreased by decreasing receiving bandwidth.
False.
Decreasing receiver bandwidth increases chemical shift artefact because the frequency differences become more pronounced over a smaller range.
Increasing receiver bandwidth reduces chemical shift artefact
By increase sampling range you can fourier transform out different frequency components
Chemical shift artefact: manifests as signal enhancement between areas of fat and water:
False.
Chemical shift artefact does not cause signal enhancement but instead misregistration of fat and water signals.
It appears as a bright and dark band at the interface between fat and water.
Or just as a signal void.
Chemical shift artefact: It can be combated by using short tau inversion recovery (STIR) sequences.
True.
STIR sequences suppress fat signal, eliminating the chemical shift artefact.
Chemical shift artefact: Reducing the FOV can be used to reduce chemical shift artefact.
TRUE.
Reducing the Field of View (FOV) increases the pixel resolution, which reduces the spatial misregistration caused by chemical shift artefact.
Smaller FOV increases sampling density, helping to minimize artefacts.
Chemical shift artefact: It can be reduced by applying a reduced encoding frequency gradient.
FALSE.
It can be reduced by using a steeper gradient.
Chemical shift artefact: The Dixon technique is used to reduce its effect.
True.
In and out of phase imaging with multiple TEs and subtraction for water and fat weight images.
Chemical shift artefact: Is seen around the kidneys.
TRUE.
Chemical shift artefact is commonly seen around the kidneys due to the interface between fat and water in perirenal fat.
Chemical shift artefact: It can be seen in fat around the optic nerve.
True.
Chemical shift artefact can occur in orbital fat around the optic nerve, appearing as bright and dark bands due to the frequency differences between fat and water.
Motion artefact occurs along the phase encoding direction.
False.
Motion artefacts predominantly occur in the phase encoding direction because phase encoding is performed over multiple TR cycles, making it more susceptible to patient movement.
Frequency encoding occurs within a single TR, so motion artefacts are less visible in the frequency encoding direction.
Magnetic susceptibility artefacts are likely to be more noticeable in gradient echo (GRE) than on spin echo (SE) images.
True
Magnetic susceptibility artefacts are more pronounced in GRE sequences because GRE lacks a 180° refocusing pulse, which in SE sequences helps to correct for local field inhomogeneities.
GRE sequences amplify susceptibility artefacts, making them more visible in areas with metal implants or air-tissue interfaces.
MRI: Aliasing often occurs as a result of the FOV being too large.
False
Aliasing occurs when the FOV is too small, not too large.
When an object extends beyond the defined FOV, signals from outside the FOV “wrap around” and appear on the opposite side of the image.
Aliasing produces a wrap around image in the frequency encoding direction.
FALSE.
Aliasing (wrap-around artefact) primarily occurs in the phase encoding direction because phase encoding samples discrete steps across multiple TR cycles.
Aliasing in the frequency encoding direction is rare and is usually corrected by ensuring proper sampling bandwidth.
Chemical shift artefact occurs in the phase encoding direction.
FALSE. Frequency direction.
Since the Fourier transform takes into account the phase difference in assigning spatial location to a signal in this direction, no water-fat misregistration will occur along the phase-encoding axis in routine spin-echo or gradient-echo imaging.
https://mri-q.com/chemical-shift-in-phase.html
Gd-DTPA is a paramagnetic contrast agent.
True.
Gd-DTPA shortens only T1 recovery time.
FALSE.
Gd-DTPA primarily shortens T1 relaxation time, making tissues appear brighter on T1-weighted images.
However, it also has some effect on T2 relaxation at high concentrations, causing a reduction in signal intensity on T2-weighted images.
Gadolinium cannot be excreted by the body
True. Hence it is used with a chelating agent such as DTPA. Gd-DTPA is formed which can be safely excreted. Gd itself is extremely toxic.
Gd-DTPA is contraindicated in sickle cell anaemia.
FALSE.
There is no specific contraindication for Gd-DTPA in sickle cell anaemia.
However, patients with sickle cell disease who have impaired renal function may be at risk of nephrogenic systemic fibrosis (NSF).
Gd-DTPA is contraindicated in pregnancy.
Gd-DTPA is contraindicated in pregnancy. ✅ True (with caution)
Gadolinium crosses the placenta and is classified as pregnancy category C, meaning risk cannot be ruled out.
Gd-DTPA should only be used in pregnancy if absolutely necessary and if the benefit outweighs the risk.
Iron oxide (Fe3O4) is a positive contrast agent.
FALSE.
Iron oxide (Fe₃O₄) is a negative contrast agent that primarily affects T2-weighted images by causing signal loss.
Area of uptake in normal tissue of iron oxide (Fe3O4) appears as a low signal.
True.
It is taken up by reticulo-endothelial system and excreted by liver.
Normal liver tissue will appear as a low signal and liver lesions will appear as a high signal on T2 weighted images.
This effect occurs because iron oxide nanoparticles create local magnetic field inhomogeneities, shortening T2 relaxation.
Dysprosium-DTPA is known as a superparamagnetic contrast agent.
Dysprosium-DTPA is classified as a superparamagnetic contrast agent, meaning it enhances magnetic susceptibility effects in MRI.
Iron oxide (Fe₃O₄) is known as a T1-enhancing agent.
False
Iron oxide (Fe₃O₄) is not a T1-enhancing agent; it predominantly affects T2-weighted sequences, reducing signal intensity.
Gadolinium-based agents are typically used for T1 enhancement.
Iron (Fe2+) with four unpaired electrons can be used as paramagnetic contrast.
True.
Paramagnetic compounds contain one or more unpaired electrons and are attracted to the poles of a magnet.
An iron ion (Fe²+) has four unpaired electrons in its d orbitals, making it paramagnetic; this is due to its electron configuration of [Ar] 3d⁶, where each of the first four d orbitals contains a single unpaired electron.
A controlled area is defined as an area where stray fields are greater than 0.2T.
FALSE.
Controlled area
5 Gauss line (0.5 mT) is drawn around the room in which the static magnetic power is greater than or equal to 5 Gauss.
Patients / staff with contraindications (pacemakers etc.) to MRI should not enter this area.
Anyone with a cardiac pacemaker should be excluded from areas where stray fields are greater than 0.5mT.
True
Patients with pacemakers should not enter areas where the magnetic field exceeds 0.5mT, as it can interfere with pacemaker function.
This is an established MRI safety guideline to prevent device malfunction.
MRI specific absorption ratio (SAR):
It is greater for large body parts.
True.
SAR increases for larger body parts because larger tissue volumes absorb more RF energy.
Static magnetic fields used can cause peripheral nerve stimulation.
Rapid changes in magnetic fields (such as those used in MRI) can induce peripheral nerve stimulation, leading to tingling sensations.
This is due to eddy currents generated in the body.
MRI: It is not recommended for pregnant patients to be scanned during the first three months of pregnancy.
True.
The theoretical risk is due to excessive heating acting as a potential teratogen.
Because of uncertainties in the RF dosimetry during pregnancy, it is recommended that exposure duration should be reduced to the minimum and that only the normal operation level is used, and to exclude pregnant women during the first three months of pregnancy.
While no proven risks have been established, radiofrequency (RF) heating and acoustic noise exposure are potential concerns.
MRI: Anaesthetized patients do not require hearing protection.
All patients, including anaesthetized ones, require hearing protection due to the high noise levels produced by MRI gradient switching.
Lack of hearing protection can cause permanent hearing damage.
MRI specific absorption ratio (SAR):
Is greater for SE than for GRE.
True.
SE sequences utilize a 90° excitation pulse followed by one or more 180° refocusing pulses, which require more radiofrequency (RF) energy. In contrast, GRE sequences use lower flip angles and rely on gradient reversals for signal refocusing, resulting in lower RF energy deposition and thus lower SAR.
MRI specific absorption ratio (SAR):
is greater for higher static fields.
True
SAR increases with higher magnetic field strengths (B₀) because the RF power required for excitation increases with field strength.
MRI specific absorption ratio (SAR):
is greater for a 180-degree pulse than a 90-degree pulse.
True
A 180-degree RF pulse deposits more energy than a 90-degree pulse, leading to a higher SAR.
MRI specific absorption ratio (SAR):
Restricting whole-body SAR to 1W/kg restricts whole-body temperature rise to 0.5°C.
True
Regulatory guidelines state that limiting whole-body SAR to 1W/kg prevents excessive heating, restricting body temperature rise to approximately 0.5°C
MRI Emergencies:
Quenching superconducting electromagnets only results in minimal downtime.
Quenching a superconducting magnet leads to significant downtime and costly repairs.
The process disrupts superconductivity, requiring extensive recommissioning.
MRI Emergencies:
Quenching does not result in damage to the superconducting magnet.
Quenching can cause severe damage to the superconducting magnet.
The rapid loss of liquid helium leads to thermal stress and potential mechanical failure.
MRI Emergencies:
When quenching occurs, the room should be shut and ventilation turned off.
False
Proper ventilation should always remain active during a quench to prevent helium gas buildup, which can displace oxygen and cause asphyxiation.
MRI rooms have quench pipes for controlled gas venting.
MRI Emergencies:
In the event of cardiac arrest in a superconducting magnet, the patient should remain in the MRI scanner with the arrest teams called in.
False. The patient should be transferred to an MR-compatible trolley and then be taken outside the control area where the arrest team can take over.
MRI Emergencies:
In case of fire, fire extinguishers can be used safely as normal.
FALSE.
Standard fire extinguishers containing ferromagnetic materials must NOT be used near an MRI scanner.
MRI-safe fire extinguishers (non-ferrous CO₂ or specific MRI-compatible models) must be used instead.
Fire fighting equipment should be used only at a safe distance which depends on field gradient, strength, and active shielding. Ideally, only carbon dioxide extinguishers should be used. Quenching should occur if firemen need to enter inner controlled areas. As a general rule, it is not advisable to take non-MRI safe equipment into the scan room.
MRI Electromagnets:
Resistive magnets can be turned off instantaneously.
True.
Resistive electromagnets can be turned off quickly by simply cutting off the power supply, unlike superconducting magnets which require controlled quenching.
A resistive magnet is a type of electromagnet used in MRI that generates a magnetic field using electrical current flowing through wire coils.
Unlike superconducting magnets, which require cryogenic cooling, resistive magnets operate at room temperature and use standard conductive materials like copper or aluminum.
MRI Electromagnets:
Permanent magnets can produce magnetic fields up to 1.5 T.
FALSE.
Permanent magnets typically operate at lower field strengths, around 0.2T to 0.5T.
1.5T is generally achieved with superconducting magnets, not permanent magnets.
MRI Electromagnets:
Permanent magnets typically weigh up to 80 tonnes.
✅ True
Permanent magnets can be extremely heavy, sometimes reaching 50–80 tonnes due to the need for large amounts of ferromagnetic material.
MRI Electromagnets:
Superconducting magnets are supercooled to absolute zero so that negligible resistance can be achieved.
False
Superconducting magnets are cooled close to absolute zero (typically 4K or -269°C using liquid helium).
Absolute zero (0K or -273.15°C) is not practically achievable.
MRI Electromagnets:
Faraday cage is used to eliminate fringe fields.
False
A Faraday cage is used to shield the MRI room from external radiofrequency (RF) interference, not to eliminate fringe fields.
Fringe fields are managed using passive or active shielding techniques, not a Faraday cage.
Shim coils are used to minimize magnetic field inhomogeneities.
True.
For imaging purposes, homogeneity in the order of 30 parts per million (ppm) is required.
FALSE.
The minimum acceptable main magnetic field homogeneity for an MRI scanner is typically considered to be around 1-2 parts per million (ppm)
For spectroscopy, more homogenous an environment is required than for standard imaging
TRUE
< 1ppm
It is the switching off of shim coils that makes a loud banging noise.
False.
The loud banging noise in MRI is caused by rapid switching of gradient coils, not shim coils.
Gradient coils generate strong Lorentz forces, leading to mechanical vibrations against the magnet structure.
Insignificant stray fields are present in superconductive electromagnets.
Superconducting magnets can produce significant stray fields; however, these are often managed using active or passive shielding techniques.
Small stray fields are present in resistive magnets compared with superconductive electromagnets.
FALSE.
Resistive magnets generally have larger fringe fields compared to superconducting magnets, which often employ active shielding to reduce stray fields.
The RF coils are positioned close to the patient in order to maximize the signal.
True
RF coils detect the signal from the patient, and placing them closer increases signal-to-noise ratio (SNR).
This is why dedicated local coils (e.g., head, knee, or spine coils) are used.
The RF coils produce a magnetic field at right angles to the main field.
True
RF coils generate an oscillating magnetic field (B1) that is perpendicular to the main magnetic field (B0).
This interaction is essential for exciting hydrogen nuclei.
The slice select (z-axis gradient) is switched on during the application of the RF pulse.
True
The slice-select gradient (Gz) is applied simultaneously with the RF pulse to ensure only a specific slice of tissue resonates.
Surface coils are part of the main scanner.
False
Surface coils are separate, external coils used for localized imaging.
They are not built into the main magnet, unlike body coils.
Staff should not be exposed to more than 1T of static magnetic field to their whole body.
FALSE.
The MHRA guidelines do not specify an exact 1T limit for whole-body occupational exposure.
However, exposure to high static magnetic fields (>2–4T) can induce transient effects such as vertigo, nausea, and metallic taste
Need to control access to areas where fringe field ≥ 0.5mT
Fringe field is not usually a problem for permanent magnets, but will need to be actively shimmed for superconducting system
Staff should not be exposed to more than 5T of static magnetic field to their limbs.
However, exposure to high static magnetic fields (>2–4T) can induce transient effects such as vertigo, nausea, and metallic taste
Similar to whole-body exposure, there isn’t a specific 5 Tesla limit for limb exposure. The ICNIRP provides guidelines, but individual susceptibility varies. It’s crucial to adhere to safety protocols to minimize exposure.
Fringe fields depend on magnetic field strength.
True
Fringe fields are influenced by the strength of the main magnetic field. Higher field strengths can result in more extensive fringe fields, which can pose safety risks if not properly managed.
The fringe field is independent of shielding.
False.
The extent and steepness of the fringe field gradient depends on the main magnet field strength, the design of magnet (open versus tunnel bore) and the shielding employed (active, passive cladding, or whole room shielding). Each installation will differ
due to the surrounding structures and therefore it is essential that staff at every MR site should have a thorough understanding of the fringe fields relating to each scanner that is on their site.
A field strength of 3mT (30 Gauss) is chosen for the inner MR controlled area to avoid the projectile hazard.
True
A field strength of 0.5mT (5 Gauss) was chosen for the MR CONTROLLED AREA to avoid interaction with medical implants.
A field strength of 3mT (30 Gauss) was chosen for the INNER MR CONTROLLED AREA to avoid the projectile hazard.
MRI Safety:
In the case of infants and persons with cardiovascular impairment, the temperature increase should not exceed 0.5°C.
True
Infants and individuals with cardiovascular impairment have reduced thermoregulatory ability, making them more susceptible to overheating.
A maximum temperature increase of 0.5°C is recommended for these vulnerable groups
MRI Safety:
There is a theoretical risk of peripheral nerve stimulation.
True
Time-varying magnetic fields induce currents in nerve cells, leading to peripheral nerve stimulation (PNS).
PNS is a well-documented effect of MRI gradient fields, especially at high gradient switching rate
MRI Safety:
There is a theoretical risk of ventricular fibrillation
Ventricular fibrillation can theoretically be induced by strong time-varying magnetic fields, but MRI scanners operate within safety limits to prevent this.
The risk of fibrillation is highest at frequencies between 10 Hz and 100 Hz, but standard MRI systems are designed to remain below these thresholds
MRI Safety:
For whole-body exposures, no adverse health effects are expected if the increase in body core temperature does not exceed 1°C
True.
The MHRA recommends limiting whole-body heating to 1°C in controlled mode and 0.5°C in normal mode
MRI Safety:
Burns are the most often reported MRI adverse incident in England.
True
Burns are the most frequently reported MRI-related adverse event in England.
These burns typically result from contact with conductive materials, improper patient positioning, or induced currents
Important in MRI Quality Assurance?
Uniformity.
True.
MHRA Guidelines
Uniformity is a critical parameter in MRI quality assurance as it ensures consistent signal intensity across the image.
Important in MRI Quality Assurance?
Ghosting.
True
Ghosting artefacts are an important consideration in MRI quality assurance, as they can arise from
- patient movement,
- gradient instability, or
- RF interference.
The guidelines emphasize identifying and minimizing image artefacts, including ghosting, as part of QA procedure
Important in MRI Quality Assurance?
Geometric distortion.
True.
Geometric accuracy is essential, particularly for applications like MR-guided interventions and radiotherapy planning.
Geometric distortion is a key quality assurance parameter and should be measured and quantified regularly
Important in MRI Quality Assurance?
Spatial resolution.
True.
Spatial resolution assessment is a fundamental part of MRI QA to ensure images maintain sufficient detail.
The guidelines emphasize monitoring resolution parameters as part of a broader QA programme
Important in MRI Quality Assurance?
Slice thickness.
True.
Slice thickness accuracy is a key component of MRI QA, as incorrect slice thickness can lead to misinterpretation of images.
‘Moving blood’ appears as a high signal on an SE sequence.
False.
This occurs because blood moves out of the imaging slice before the refocusing pulse can be applied, preventing signal detection sequences produce a high signal in blood.
Gradient Echo (GRE) sequences do not use a 180° refocusing pulse, meaning blood flow remains bright as there is less dephasing and more signal retention.
Gradient echo sequences produce a high signal in blood.
True.
Gradient Echo (GRE) sequences do not use a 180° refocusing pulse, meaning flowing blood retains high signal intensity, making it ideal for MRA
Time of flight angiography uses a gradient echo sequence with a very short TR.
TRUE.
ToF MRA uses short TR GRE sequences to maximize inflow enhancement, keeping moving blood bright while suppressing stationary tissues.
In phase-contrast MRA, the gradient strength may be adjusted to make the sequence sensitive to slow or fast flows.
TRUE.
Phase-contrast MRA (PC-MRA) adjusts velocity encoding (VENC) gradients to optimize sensitivity for slow or fast blood flow, allowing measurement of different flow velocities.
A STIR sequence is used to suppress a high signal such as that from fat.
True.
True. Although it is not specific to it, i.e. fat, methaemoglobin, melanin, lesions enhanced by gadolinium.
Short Tau Inversion Recovery (STIR) using an inversion recovery sequence with a short TI (inversion time)
Tissues with short T1, such as fat, will always appear dark on time-of-flight (ToF) angiography.
FALSE.
Fat has a short T1 and can appear bright on ToF MRA unless fat suppression is applied.
ToF MRA often uses fat saturation techniques to reduce bright fat signal and enhance vascular contrast.
Diffusion-weighted imaging utilizes the restriction of Brownian motion of water molecules to give a signal.
True.
Diffusion-Weighted Imaging (DWI) detects variations in the Brownian motion of water molecules, providing high signal in areas with restricted diffusion, such as acute stroke
Sequences Suitable for Gadolinium-DTPA
A diffusion-weighted imaging sequence on its own is normally sufficient for the interpretation of restricted water diffusion.
FALSE.
DWI alone is not always sufficient;
Apparent diffusion coefficient (ADC) maps are used alongside DWI to differentiate true restricted diffusion from T2 shine-through effects
Intracellular methaemoglobin appears as a high signal on T1-weighted images.
TRUE.
Intracellular methaemoglobin has paramagnetic properties, causing T1 shortening and appearing bright on T1-weighted images
Sequences Where Gadolinium Is NOT Recommended
Gadolinium-DTPA is normally used with a STIR sequence.
FALSE.
Gadolinium-DTPA should not be used with STIR sequences because STIR uses a non-selective inversion recovery pulse, which also nullifies gadolinium-enhanced tissues, reducing contrast enhancement
A fat saturation sequence uses an RF pulse centred on resonance frequency.
TRUE.
Fat saturation uses an RF pulse tuned to the resonance frequency of fat protons, allowing selective pre-saturation of fat signal before the main imaging sequence
A fat saturation sequence requires a homogenous field.
True.
Fat saturation techniques require a homogeneous magnetic field because field inhomogeneities cause incomplete fat suppression, leading to uneven image contrast
STIR is usually combined with a fast spin echo.
TRUE.
STIR (Short Tau Inversion Recovery) is often combined with Fast Spin Echo (FSE) sequences, which improve image contrast and reduce scan times.
Melanin appears as a high signal on T2-weighted images
False.
Melanin appears as a high signal on T1-weighted images, not T2. On T2-weighted images, it is typically low or intermediate in signal
Superparamagnetic iron oxides are known to cause back pain.
True.
Frequent side effect and may require stopping infusion.
Gd-DTPA has been reported to cause nephrogenic systemic fibrosis.
Gadolinium-based contrast agents (including Gd-DTPA) have been linked to nephrogenic systemic fibrosis (NSF) in patients with renal impairment.
The MHRA recommends caution in patients with kidney disease and avoiding high-risk agents in those with GFR <30 mL/min/1.73m²
A water-suppressed STIR sequence is used in silicone breast imaging.
True.
STIR sequences can be used in breast MRI, including silicone breast imaging, to suppress fat and enhance lesion detection. Water suppression in STIR improves contrast in silicone breast implant assessment
Manganese chelates are taken up by normal tissue and excreted in bile.
True. Manganese chelates are known as hepato-biliary contrast agents and normal tissues that take up contrast will display a high signal on T1.
Manganese-based contrast agents are hepatobiliary agents, meaning they are absorbed by NORMAL liver tissue and excreted in bile, making them useful for liver imaging.
Functional MRI sequences are normally acquired using the ultrafast echo planar (GE-EPI) sequence.
True.
Functional MRI (fMRI) relies on gradient-echo echo-planar imaging (GE-EPI) due to its high-speed acquisition capability, which is essential for detecting blood oxygen level-dependent (BOLD) contrast changes
This is to cope with the constraints of temporal resolution and T2* sensitivity.
