Radiology Flashcards
What is a radiograph?
An image produced by X-rays passing through an object and interacting with the photographic emulsion on a film. If a digital image is being formed, the X-rays affect a sensor or a phosphor plate.
What do the X-rays have an affect on in digital radiography?
A sensor or phosphor plate
Why are X-rays used in Dentistry?
allow us to look inside the body particularly at mineralised tissues. Teeth are mineralised (enamel more so than dentine). Caries and other dental diseases can cause demineralisation.
What can cause demineralisation?
Caries
What are the two main groups of radiographs?
Intra-oral and Extra-oral
Explain intra-oral radiographs
Film or sensor placed inside the mouth next to the area of interest and a radiation source is directed at the area from an external position.
What are the three main types of intra-oral radiographs?
Periapicals, bitewings and occlusals.
Explain extra-oral radiographs
Nothing is placed in the mouth instead both the radiation source and image receptor are positioned externally. The most common type is a DPT.
What is the most common type of extra-oral radiograph?
DPT
Describe the discovery of X-rays
November 1895, Wilhelm Conrad Roentgen discovered X-rays. Imaged his wife’s hand December 22 1895. Paper published 28th December 1895.
When was the first recorded case of adverse effects of radiation?
March 1896, New England Journal of Medicine - reported a woman had imaging of face and after her hair began to fall out, her skin became swollen, cracked and inflamed and she felt generally unwell.
When were radiographs first used in Dentistry?
1896
Describe the composition of the atom
Nucleus containing protons and neutrons. Overall the nucleus has a positive charge.
Electrons which have a negative charge orbit the nucleus in different energy shells eg. K, L, M etc.
Are the number of electrons in each shell of an atom limited?
Yes, each shell contains a maximum number of electrons.
How many electrons are in the following shells? K, L, M, N, O
K=2 L=8 M=18 N=32 O=50
What is the forbidden zone in an atom?
Electrons can move from shell to shell but cannot exist between shells - the forbidden zone.
What is the binding energy?
Electron binding energy, also called ionization potential, is the energy required to remove an electron from an atom, a molecule, or an ion.
What keeps the electrons in their shells?
Their binding energy. This energy must be overcome to remove an electron from the atom.
Which electrons have the highest binding energy?
Electrons in the outer shells have the highest binding energy however, as they are further from the nucleus they often move out from their shells into the areas between the atoms and can form bonds to form molecules.
What is an isotope?
An atom with the same amount of protons but a different number of neutrons.
What is the atomic number Z?
The number of protons
What is the atomic number N?
The number of neutrons
What is the atomic mass number?
Z+N the number of protons plus the number of neutrons
What is a radioisotope?
An isotope with an unstable nuclei which undergoes radioactive disintegration.
What do protons and electrons in an atom have in common?
An atom contains equal numbers of protons and electrons.
For the symbol of an atom where is the mass number written and where is the atomic number written?
The mass number is at the top (Z+N)
The atomic number is at the bottom (No. of protons)
The atomic number of a sodium atom is 11 and its mass number is 23. Calculate the number of protons, neutrons and electrons it contains.
Protons = 11 Neutrons = 12 Electrons = 11
What is an ion?
A charged atom or molecule. The number of electrons does NOT equal the number of protons. eg. anion or cation
What is an anion?
An ion where there are more electrons than protons so therefore a negative charge.
What is a cation?
An ion with more protons than electrons so therefore a positive charge.
Name the three main radioactive emissions
Alpha particles, Beta particles, Gamma rays
Describe an alpha particle
2 protons and 2 neutrons (helium nucleus) Size - Large Charge - Positive Speed - Slow Penetration - 1-2mm in tissue Energy - 1-8MeV (mega electron volts) Damage potential - extensive ionisation
Describe a beta particle
Electrons (fast electrons) Size - small Charge - negative Speed - fast Penetration - 1-2cm in tissue Energy - 100keV-6MeV Damage potential - ionisation
Describe gamma rays
Electromagnetic radiation Size - Nil Charge - Nil Speed - very fast Penetration - can pass through tissue Energy - 1.24keV-12.4MeV Damage potential - ionisation
Describe the X-rays used in dentistry
Do not occur naturally. Not involved in radioactive decay. Not particulate - no mass or weight Very fast No charge. Identical to gamma rays with lower energy values. Cause ionisation.
When is ionisation a problem?
When it occurs in living cells.
Can cause damage to tissues - eg. cataracts
Can cause damage to DNA directly or produce chemicals that do this damage - tumours or cancer.
What does the electromagnetic spectrum base the spectrum on?
The properties of different parts of the spectrum depend on the wavelength of the particular area eg. radiowaves large wavelength, Gamma rays short wavelength
How fast does radiation in the electromagnetic spectrum travel?
At the speed of light. (299,792,458m/s)
What mass does radiation in the EM have?
No mass.
What is a photon?
A packet of energy.
What is energy measured in?
Electron volts (eV) or volts (V)
What is frequency measured in?
Cycles per second or Hertz (Hz)
What is wavelength measured in?
Metres or nanometres (10 to the -9)
What is the wavelength of visible light?
400-700nm
What is the wavelength?
the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave. S-shaped.
What is the frequency?
Frequency is the number of waves that form in a given length of time. It is usually measured as the number of wave cycles per second, or hertz (Hz).
What is the formula for frequency?
Frequency (Hz) = cycles/seconds
What is the domestic electrical supply?
220/240 volts 13 amp current (usually) 50Hz circuits can be fused at 3, 5 or 13 amps. Cookers etc have 30 amp circuits.
What is the SI unit of voltage?
Volt
What is voltage?
the power or force that causes a current to move along a wire of for electrons to move across a gap from a cathode to an anode.
What is 1 volt?
1 volt is the potential difference between 2 points on a conducting wire, carrying a constant current of 1 amp when the power dissipated between the points is 1 watt.
What direction does current pass along a wire?
from -ve to +ve.
Is electricity supply in one direction?
No electricity supply is alternating.
How is current passed along a wire?
By the vibration of electrons.
Describe the conversion of energy
Energy is not created nor destroyed, it can only be changed from one form to another.
Describe the basic principle/make up of a dental radiograph.
X-ray source, object, receptor.
Name the two types of bitewings
Horizontal or vertical
Name the two types of occlusals
maxilla or mandible
Name 5 extra oral radiographic techniques
DPT Lateral cephalogram Posterior-anterior mandible Lateral-oblique mandible Occipito-mental views of facial bones
Name some of the uses of peri-apicals
Detect apical infection Assess periodontal problems Trauma - fractures of tooth or bone Morphology pre extraction Position/presence of unerupted teeth Endodontics Pre-post apical surgery Evaluation of implants
Name the two different techniques of peri-apicals and their differences
1) Paralleling technique periapical use holders for positioning receptor parallel to tooth accurate/reproducible image 2) Bisected angle periapical can be done without holder operator dependent not reproducible
What is the periodical technique of choice?
Paralleling technique
Explain the paralleling technique for periapicals
uses holders to facilitate positioning
allows accurate geometry of image
receptor parallel to tooth
X-ray beam perpendicular to tooth/receptor
minimises magnification
accurate/reproducible image
holders are bulky and may not be tolerated by all patients.
Can reduce patient dose to patient by reducing repeats and does not expose patients fingers (see bisected angle periapicals)
Name the two types of receptor
digital or film
Name the different parts that make up the holder
bite block - retains the receptor
indicator arm/rod - fits into bite block
Aiming ring - slides onto arm to establish alignment of collimator with receptor
Name two types of holder you can get
Anterior or posterior
What to the holders allow?
Accurate geometry of image
How is the vertical plane of the film positioned in relation to the tooth?
the vertical plane of the tooth should be positioned so that it is parallel to the long axis of the tooth.
Film and tooth parallel vertically
How is the horizontal plane of the film positioned in relation to the tooth?
horizontal plane must be parallel to the dental arch under examination.
How does distortion of an image occur?
If the tooth and film are not parallel
At what angle should the X-ray beam be in relation to the tooth/receptor?
At 90 degrees, right angle.
Name two types of distortion
elongation and fore-shortening
What can affect the image size (magnification)?
1) X-ray source (focal spot) to receptor distance
2) Object (tooth) to receptor distance
What are three things to think about when taking the X-ray?
Receptor position - horizontal and vertical
Beam alignment - horizontal and vertical
Distance
In what orientation should an image receptor be in the posterior region?
Horizontally/ Landscape
In what orientation should an image receptor be in the anterior region?
Vertically/portrait
Name four barriers to good positioning
Mouth size
Film size
Gag reflex
Digital sensor size and shape
Name the four most common sizes of film/PSP receptor
0, 1, 2, 4
What size film should be used for an adult bitewing (horizontal or vertical)?
2 only
What size film should be used for a child’s bitewing? under 10 and then over 10
Under 10 -> 0 or 1
Over 10 -> 2
What does the dot on a radiographic film represent?
Left or Right
Periapical - towards the crowns of the teeth
Bitewing - towards the palate
What does IRR17 and IRMER17 stand for?
Ionising Radiations Regulations 2017 (IRR17) and Ionising Radiation (Medical Exposure) Regulations 2017 (IRMER17)
Where in the X-ray machine are the X-rays produced?
The tube head is where the domestic electric supply is converted into ionising radiation so that we can produce the X-rays.
What is the potential difference between the cathode and the anode?
70kV
What charge does the anode have?
Positive
What charge does the cathode have?
Negative
Where is the filament?
At the cathode
What is the cathode made of?
It is a very fine wire made of tungsten - high mp and high tensile strength
Explain the workings of the cathode
Firstly the domestic supply current (13A) goes through a step down transformer small current passed along it 8-10mA electrons are excited - they vibrate wire gets hot - may give off light excited electrons lost from outer shells electrons form cloud around cathode
What is the anode made of?
Small tungsten target embedded in copper
Explain what happens at the anode
-ve electrons bombard +ve anode
high energy electrons come to sudden stop or decelerate and energy form changes.
99% heat, 1% X-rays
Why is tungsten chosen for the anode?
it will give rise to X-rays in the wavelength or power required for dental imaging.
Explain the use of a step up transformer at the anode
Domestic supply is 240V so we need to increase it with a step-up transformer within the tube head again which is made out of copper coils.
Name the two types of X-ray spectra
Continuous spectra - Bremsstrahlung or breaking radiation, wide range of photon energies
Characteristic spectrum - emitted by loss of electrons from K and L shells, depends on material in anode
Name the other two names for a DPT
OPG, OPT
What happens during Bremsstrahlung (continuous spectrum) radiation production?
An electron from the cathode is attracted to the positively charged atom of tungsten in the anode. As it moves round the nucleus it loses its energy, maybe not all of it but there will then be an electron with much less energy moving off to react with other atoms, much of the energy given off is heat but you also get some Bremsstrahlung radiation produced too.
Name some of the features of continuous spectrum radiation (Bremsstrahlung radiation)
wide range of photon energies
small deflections most common - many low energy photons
little penetrating power - need filtering out
large deflections less likely - few high energy photons
Maximum photon energy directly related to kV across X-ray tube
Explain the reason for the wide range of photon energies in continuous spectrum radiation
There are multiple electrons being attracted towards the anode and so we get multiple reactions and multiple X-ray photons being produced. These all have a wide range of energies.
Explain the energy of photons produced in small deflections in the continuous spectrum and their effect on the body
when there is a small deflection around the nucleus (most common), we have low energy X-ray photons produced. They have little penetrating power and would be absorbed by the body therefore they need to be filtered out as it is absorbed radiation that gives rise to X-ray dose.
What gives rise to the X-ray dose?
The absorbed radiation
Explain large deflections of photons in the continuous spectrum
Large deflections are less likely and give rise to high energy photons, therefore there are going to be few of them produced.
What is the maximum photon energy produced directly related to?
the kV used across the X-ray tube
Explain how characteristic radiation is produced
for characteristic radiation to be produced an incident electron has a direct hit with an electron in the K shell, it knocks the K shell electron out which is called the ejected orbital electron. The initial electron may also be expelled from the atom as an inter-incident electron and it may have less energy now. The K shell is now deficient of one electron so it is unstable, therefore an electron from the L shell falls down to fill the space. However, that electron has too much binding energy so it gets rid of the excess energy as an X-ray photon. The gap in the L shell is then filled by an M shell electron and so on until you reach the outer shell.
What photon energy level is needed in a dental X-ray machine?
X-ray tube needs to be operating above 69.5kV for the characteristic spectrum to be produced.
If you are using a dental X-ray tube that works between 60-65kV what kind of radiation is produced?
only Bremsstrahlung radiation not tungsten characteristic radiation
X-rays are a part of what spectrum?
The electromagnetic spectrum
What two categories is the EM spectrum split into?
Ionising and non-ionising radiation
Discuss the link between energy, wavelength and ionising vs non-ionising radiation
the larger the wavelength the more likely we are to be talking about non-ionising radiation
as wavelength gets shorter, energy of photons increases and this is where ionising radiations form
Define scattering
random change in direction after hitting something
Define absorption
deposition of energy in tissues (represents dose)
Define intensity
number of X-ray photons in a defined area of the beam - further we are from the source, the more the intensity of photons decreases
Define attenuation
reduction in intensity of beam due to scattering and absorption
Define ionisation
removal of electron from a neutral atom to give -ve and +ve (atom) ions.
Define penetration
the ability of photons to pass through or into tissues/materials
Name 4 X-ray interactions
1) completely scattered with no loss of energy
2) absorbed with total loss of energy
3) scattered with some absorption and loss of energy (mix)
4) transmitted unchanged (no scattering, no absorption, no loss of energy)
What is internal scatter?
radiation passing down and scattered elsewhere in the patient’s body
What features do X-rays have in common with visible light?
it travels in straight lines in free space X-ray photons form a divergent beam can travel through a vaccum Penetrate matter can be absorbed
What features do X-rays not have in common with visible light?
Not detectable by human senses produce a latent image on film emulsion Cause ionisation can cause biological damage cause certain salts to fluoresce and emit light
What is the radiation dose?
the radiation dose is the amount of radiation absorbed by the patient.
What kind of photons are absorbed by soft tissues?
Low energy photons - therefore they are the ones most likely to cause damage
What do different types of electromagnetic radiations properties depend on?
Their wavelength
Is biological harm limited to ionising radiation?
No - people believe microwaves can also be damaging and they are a type of non-ionising radiation
What is an image receptor?
the technical term for the item the X-ray image is formed on ie. film, plate or digital sensor
What causes fogging of a film?
some photons do not have enough energy to make a useful interaction with the receptor and this scatter can degrade the image.
When was the first permanently fixed image taken?
1827 and it required an exposure time of 8 hours.
What are the two ways we now use to capture X-ray images?
Film or Digital
What are the two sub-categories of Film X-rays?
Direct action film and indirect action film
What are the two sub-categories of Digital X-rays?
Solid state sensor and photo-stimulable phosphor
Describe a direct action film
Dental intra-oral. X-rays act directly on silver halide crystals in film emulsion.
Describe an indirect action film
Dental Extra-Oral. Light from intensifying screens act on silver halide crystals in film emulsion. The X-ray photons react with the intensifying screens to produce photons which expose the film to produce the image.
Describe how a solid state CCD or CMOS sensor works (types of digital X-ray)
CCD = Charge-coupled device
CMOS = complimentary metal-oxide semiconductor
They work by converting light into electrons. The info is then collected by a computer programme and made into an image.
Describe how a PSP works (type of digital X-ray)
PSP = Photostimulable phosphor plate
Latent image produced by interaction of X-rays with phosphor layer on plate. The phosphor coating is exposed to X-rays which causes a reaction with the phosphor which is known as the stable excited state.
The plate is then dropped into the vista scan unit where it is scanned by a red laser. This is then the unstable excited state. The blue light emitted is collected and converted into the image.
What does a vista scan tower do?
Scan PSP Plates
Name differences between PSP plates and solid state sensors
Phosphor plate = used with existing film holders, tolerated well by patients, plates easily damaged, relatively expensive, sensitive to background radiation
Solid state sensor = only used with its own holders, not tolerated well by patients, sensors are very expensive, easily damaged, image resolution better than PSP.
Describe the two sides of a PSP
one pale side with a phosphor coating (coating can be of various compounds eg. barium fluoride). This is the side the image is formed on.
Other side is black and shows size of film and orientation dot. This is the back of the plate.
Explain the production of an image on PSP plates
Phosphor layer exposed to X-rays
X-ray energy stored in electrons of phosphor crystals (trapped signal) - latent image
plate inserted into scanner
phosphor layer scanned by red laser
stored energy released as blue light
light detected by photodetector and sent to signal digitiser (ADC = Analogue to digital converter)
ADC converts light to digital signal - each pixel assigned numerical value according to intensity
Numerical values represent different shades of grey which are used in image.
After a PSP plate has been used how is it cleared to be re-used?
After a PSP plate has been scanned and image obtained there is still residual trapped energy in phosphor electrons after scanning. Image on plate is erased by exposing phosphor to bright light (releases any remaining trapped energy in phosphor electrons).
Plates then ready to re-use.
Name the four layers in a Charge coupled device detector
Front to back
Front cover, scintillator layer, silicon wafer, back cover
Describe the role of the 4 layers in a CCD detector
Front cover
Scintillator layer - converts X-ray energy to light
Silicon Wafer - converts light into electrical signal
Back cover - often incorporates a cable to carry signal to PC (or wireless)
What is the scintillator layer in a CCD detector made of?
either caesium iodide or gadolinium oxysulphide
Describe how CCD creates X-ray image
X-rays hit scintillator layer (caesium iodide or gadolinium oxysulphide)
reaction gives off light which hits photosensitive cells in silicon wafer layer
electrons within each cell (pixel) are released and these form a charge (voltage) which its converted into an image by the computer.
Each cell is connected to its neighbour and the signal converted to the image is from a line of neighbouring cells.
Describe the difference between CCD and CMOS
CMOS is very similar to CCD
Only difference is that the photocells are electrically isolated therefore a signal (voltage) is sent from each individual cell (pixel) rather than a line of cells (pixels).
What is an issue with digital images?
There is no orientation dot. With many radiographs it can get confusing and be easy to look at an image in the wrong orientation.
Which has better image quality - CCD or CMOS?
CCD but CMOS catching up
Which is cheaper to manufacture - CCD or CMOS?
CMOS
Which has been around longest - CCD or CMOS?
CCD
Which uses less power - CCD or CMOS?
CMOS
Name some advantages of digital imaging
No chemicals, faster processing, easy archiving, easy image transfer, image manipulation, dose reduction
Name some disadvantages of digital imaging
expensive-damage, reduction in resolution due to pixel size, archiving-back up, easy image transfer-security issues, image manipulation, dose reduction-shorter exposure=drop in image resolution
What kind of exposure have you given if the image is too dark?
High exposure, too much radiation given
What kind of exposure have you given if the image is too pale?
Low exposure, not enough radiation
Can radiographs be stored as just one copy?
No, there must be some form of back-up to allow access to images in case something goes wrong, eg. CD, DVD, remote hard drive
What archive system does DDH use to store radiographs?
PACS - Picture Archiving and Communication System
Explain how PACS works
Most NHS hospitals in Scotland subscribe to a company called Carestream to provide PACS. In Tayside, images are initially uploaded to the local PACS and then national PACS server which is in Livingstone. Therefore you can access them anywhere in Scotland as long as the hospital uploads to PACS.
What unique accession number on PACS do DDH images start with?
T113H
What size of digital receptor is used for anterior mouth periapicals in adults?
0 or 1
What size of digital receptor is used for posterior mouth periapicals in adults?
2
What size of digital receptor is used for occlusals?
4
What size of digital receptor is used for periapicals in all regions for children?
0 or 1
What size do solid state CCD or CMOS receptors tend to come in?
Tend to come in size 2 only. Can make X-raying anterior teeth more difficult due to the size of receptor.
Who is the man who claimed he was “immune” to radiation and also has many patents to his name relating dentistry?
Dr Edmund Kells - Dentist in New Orleans
Prolific inventor - eg. surgical aspirator, 40+ patents
1885 employed first female dental assistant
Supported conservative cavity prep
suggested “saving” pulp-less teeth
1st to take radiographs in America
Noticed adverse effects of radiation on hands of other dentists but claimed he was immune. He later suffered changes to skin and lost a number of fingers to surgery and developed a tumour on his hand.
Regarding the biological effects of radiation, define deterministic effects (non stochastic)
Those we know WILL occur
Regarding the biological effects of radiation, define non-deterministic effects (stochastic)
Those which MAY occur
Explain deterministic effects of radiation and the threshold dose
Deterministic effects definitely occur with specific doses
Threshold dose - below this the effect does not occur
SOMATIC effects
Radiotherapy - use of somatic effects in positive way
Name the two types of deterministic effects and what they involve
1) Acute - radiation sickness 2-10Sv whole body irradiation. Death >10Sv whole body irradiation
2) Chronic - hair loss, cataracts, sterility, obliterative endarteritis
Explain non-deterministic effects of radiation including examples of somatic and genetic effects
non-deterministic effects of radiation occur at random.
There is no threshold dose.
Damage affects patient and future children.
Amount of damage not related to dose.
Somatic effects - development of malignancy
Genetic effects - congenital abnormality which may include malignancy.
For genetic effects to occur reproductive organs need to be exposed to radiation.
Which type of radiation effects are we likely to have in dentistry?
Non-deterministic - this is the issue.
We do not expose patients to sufficient radiation to reach threshold dose.
In the UK what % of all X-ray examinations are taken by the GDP?
estimated 26%
In 2008 how many dental radiographs were taken?
20.5 million
What are the three factors that affect the dose of radiation?
1) Type of radiation (we only use X-rays)
2) Tissue being irradiated (diff tissues diff sensitivity)
3) Age of the patient
What is the typical effective dose in mSv for a bitewing/periapical?
0.0003-0.022mSv
What is the typical effective dose in mSv for a DPT?
0.0027-0.038mSv
What is the typical effective dose in mSv for a maxillary occlusal?
0.008
What is the typical effective dose in mSv for a lateral cephalometric?
0.0022-0.0056
What is the typical effective dose in mSv for a craniofacial CBCT?
0.03-1.1
What is the typical effective dose in mSv for a CT mandible and maxilla?
0.25-1.4
What is the recommended dose limit per annum for a dentist?
1mSv (same as general public)
What is the recommended dose limit per annum for a classified worker?
20mSv
What is the recommended dose limit per annum for a non-classified worker?
6mSv
What is the recommended dose limit per annum for the general public?
1mSv
What does ALARP stand for regarding the dose limits for patients?
As Low As Reasonably Practicable
Will there be people who die as a result of their exposure to radiation in dentistry?
Although the risks from ionising radiation in dentistry are low, there are still a number of people who will die yes.
What is the estimated risk of developing fatal malignancy from X-ray Examination using a dental intra-oral 70kV, D speed, round?
1 in 1 million
Explain the link between age and the risk of developing adverse effects from radiation
The younger a patient is, the greater the risk of developing adverse effects.
Provide the multiplication factor for risk of cancer by ages <10 10-20 20-30 30-50 50-80 >80
<10 = 3 10-20 = 2 20-30 = 1.5 30-50 = 0.5 50-80 = 0.3 >80 = negligible
What percentage of the estimated average UK dose is made up from medical and dental?
15%
Name some foods that are radioactive
Brazil nuts, butter beans, bananas, potatoes, carrots, red meat, avocado, beer, water, peanut butter - mainly from radioactive potassium
What does BED stand for?
Banana equivalent dose
What is 1 banana equivalent to as the percentage of average daily exposure?
1%
In terms of BED, how many BED make up the average daily exposure?
100 BED
How many BEDs are there in a Chest CT scan?
Chest scan = 70,000 BED = 7mSv
What two things must we weigh up every time we need to take a radiograph?
the information vs the radiation dose to the patient
Provide some practical means of dose reduction
avoid unnecessary radiographs
use of selection criteria
film speed - preferably use F speed
kV of machine - higher the kV, lower the dose
Rectangular collimation - keeps dose lower than round beam
Collimated DPT viewer - restricts beam to area of interest
Regular servicing of machines
Does a higher or lower kV of machine produce a lower dose of radiation?
The higher the kV of the machine, the lower the radiation dose to the patient.
Explain intensity and the inverse square law
The further away we are from the source, the less likely we are to be exposed to many X-ray photons.
The intensity of radiation is proportional to 1/(distance squared)
ie. you double the distance then you have quarter the intensity across the area
What is the controlled area?
The area around the patient and the X-ray tube where only the patient should be present, the rest of the controlled area should be considered a no go zone.
