Introduction to Radiology Flashcards
What are X-rays
X rays are a form of high energy electromagnetic radiation that can be produced in packets of energy called photons.
Name the different types of waves on the EMS from longest to shortest wavelength
Radiowaves Microwaves Infra Red Waves Visible light Ultra violet rays X rays (ionising) Gamma rays (ionising)
What is ionising radiation
This is radiation that has enough energy to detach electrons from atoms and molecules
In which direction do x-rays travel
In a straight line
How are x-rays produced
High-speed energetic electrons bombard a target material and are brought suddenly to rest
What are the functions of the cathode and the anode in an x-ray tube
The cathode produces electrons
The anode acts as a target for electrons and converts the high energy electrons into x-ray photons
What happens in an x-ray tube
- the cathode filament is heated and electrons are emitted by the hot filament
- These electrons travel to the anode
What is the cathode filament made out of
Tungsten
What is tube current and how is it measured
Tube current is the flow of electrons from the cathode to the anode and is measured in milliamperes (mA)
Why is a high voltage used between the cathode and the anode
To accelerate the electrons to provide the energy needed to remove an electron from the K shell of a tungsten atom
What is the targets in the anode made from and why
It is a small piece of tungsten, which is set into the angled face of a large copper block
The copper is used to allow the efficient removal of heat
Why do we use a vacuum chamber in an x-ray tube
Air molecules would block or scatter the electrons away from the target
What are the two types of x-ray producing collisions with the tungsten atom
Continuous spectrum
Characteristic spectrum
What is continuous spectrum x-ray production
This is when the high-speed electrons collide with a tungsten atom and slow down and change direction as they interact with the positively charged nucleus and produce an x-ray as they lose this energy
What is the name of the radiation produced in continuous spectrum x-ray production
Breaking radiation (bremsstrahlung radiation)
How does characteristic spectrum x-ray production work
Electrons collide with the K-shell electrons (strongest binding) in tungsten and if the displace it or move it to another electron shell
What is the critical voltage in an x ray tube
69.5 KV
What is combined spectrum x ray production and when is it used
Combined = characteristic + continuous and is used when the x ray tube uses above 69.5 KV.
What is scattering in terms of radiology
This is a change in the direction of photons with or without the loss of energy
What is absorption in terms of radiology
This is the deposition of energy like removal of energy from an atom
What is attenuation in terms of radiology
This is a reduction in the intensity of the main x-ray beam caused by absorption and scattering
Name and describe the different types of interaction and x-ray can have with patient tissue
- Unmodified/Rayleigh Scattering - Pure scatter = scatter without change
- Photoelectric effect = pure absorption*
- Compton effect = scatter + absorption*
- Pair production = pure absorption
How is heat produced in the X ray tube
When electrons change direction by colliding with outer shell tungsten electrons lose energy and form heat
Why does heat need to be removed in an X ray tube
To prevent damage to the target
Name some uses of X rays in dentistry
- Developing dentition
- Caries Diagnosis
- Periodontal assessment (bone level)
- Endodontics
- Trauma
- Implants
What is radiation absorbed dose, name its units and what is used to measure it
This is the amount of energy absorbed from the radiation beam per unit mass of tissue it is measured in milligray (mGy)
measured using dosimeter
What is equivalent those and what are the units
This is the dose quantitiy for individual organs and is based on the absorbed dose to an organ
Unit = sievert (Sv)
What is the calculation for equivalent dose (Ht)
radiation absorbed dose x radiation weighing factor (Wr) of a particular tissue
What is the radiation weighing factor (Wr)
This represents the biological effects of different radiation on different tissues.
more absorption into the tissue = higher value.
What is the radiation weightings factor (Wr) for x-rays, gamma rays and beta particles
1
What is a tissue weighting factor (Wt)
This is a value assigned to each organ to represent how likely it is to be damaged by radiation, higher factor = higher risk
How can age affect risk of radiation
Risk is reduced as you get older, when you are young the risk is much higher.
What are the classifications of the potential biological effects of x-rays
- somatic deterministic
- somatic stochastic
- genetic stochastic
What are somatic deterministic effects
These are the damaging effects to the body that definitely results from a high specific dose of radiation
The higher the dose the more severe the effect and in most cases below a certain threshold dose there will be no effect
What are somatic stochastic effects and gives some examples
These are effects that occur by chance and their development is random - leukaemia and certain tumours
How can indirect damage occur from x rays
Water in cells are ionised and cause free radicals to form Hydrogen peroxide and hydroperoxyl that can damage DNA
AY BAWS CAN I HABE DE NOTE PLZ
must be able to clinically justify the use of X rays
What are the 4 techniques used to reduce x ray doses
- Equipment
- Clinical Decision
- Practical Technique
- Diagnostic Interpretation
What is Aluminium Filtration used for in X rays
To remove harmful low energy x rays (soft x rays)
Why are soft x rays harmful
they dont really pass through and get absorbed
What is a collimator and what does it do
This is a metal barrier that has a hole that reduces the size and shape of x ray beam, it minimises scattered radiation, provides sharper image, less exposure innit
What are the different types of collimator
Diaphragm, round, rectangular and slit,
rectangular is most effective at reducing radiation
What are the 3 principles of radiology use defined by the International Commission on Radiological Protection (ICRP)
- Justification - availability and findings of previous radiographs, objectives of treatment, level of benefit to patient, alternative techniques
- Optimisation - all exposures kept as low as possible
- Limitation - equivalent dose shouldnt exceed limits recommended by the ICRP to protect, patients, radiation workers and general public
How often should X ray tubes and all be checked
1-3 years
What is a Beam Indicating Device (BID) and what is it used for
used for indicating the direction of the beam
setting ideal distance from focal spot on the target to skin
What is a focusing device used for
Aims the stream of electrons at the focal point on the target
Why is lead used in radiation protection
Has a high atomic number so the probability of photoelectric interactions is quite high
What is the penumbra effect and how does it relate to X ray use
Means that the focal spot (source of the x rays) should be a single point source to reduce blurring of the image
What is the voltage of the main supply to the tube voltage (KV)
240V
How is the voltage of the main supply to the tube voltage (KV) altered in the X ray tube
Step up transformer = higher voltage to accelerate electrons = more compton effect, higher penetrating energy of photons, so less absorbed energy and less damage to tissue
Step down transformer= low voltage used to heat the filament
What is film speed and what determines it
This is the sensitivity of the radiograph to radiation
- size of the silver halide crystals
- thickness of emulsion
- presence of radiosensitive dyes
What are the speeds of film categorised as and what is the fastest
D, E and F
F is the fastest
How can digital imaging be used to reduce dose
Both types of digital image receptors are much more
efficient at recording photon energy than conventional
film.
Gives an example of direct digital imaging
- Sensor or imaging plate, replacing conventional film
Give examples of indirect digital imaging and roughly how they work
- Real time/corded CCD
- Cordless, photostimulated phosphor plates (PSP)
scanning and digitalising a film captured image
How do solid state sensors compare to PSP sensors and why do PSP sensors
solid stat sensors allow much more dose reduction as PSP sensors have a wide dynamic range (latitude), which can result in higher doses
Should lead aprons be used routinely in dental radiography
no there is no justification and is positively discouraged
How can pregnancy affect dental radiography
the associated risk is regarded as negligible but patient is given option of delaying radiography due to emotive nature
What does IRMER stand for
Ionising Radiation (Medical Exposures) Regulations
What is the role and duty of the referrer in X rays stufffs
A health professional is entitled to refer a patient for medical exposure and must supply sufficient info to justify an exposure
What is the role and duty of the practitioner in X rays stufffs
Health professional entitled to take responsibility for a medical exposure
What is the role and duty of the operator in X rays stufffs
Pratical element of medical exposure, exposure of radiograph and processing film
What is the role and duty of the employer in X rays stufffs
Ultimate responsibility for a radiological installation
Who should you notify if there is a radiograph equipment malfunction
Health and Safety office
Who should you notify if there is a clinical error, error of judgement, operator error
IRMER inspectorate
