BDS3 X-ray physics and other things Flashcards
What is EM radiation?
Movement of energy as photons
Measured in eV
What is the difference between gamma radiation and X-rays?
Essentially the same but gamma radiation occurs naturally and X-rays are man-made.
How are X-rays produced?
Electrons are fired at atoms at a very high speed.
On collision, kinetic energy is then converted into high energy EM radiation and heat
ESSENTIALLY
Atoms that have been EXCITED emit packages of energy called PHOTONS (x-ray photons).
What are the types of x-rays?
HARD - higher energies, able to penetrate human tissues - medical imaging mostly uses this
SOFT - lower energies - easily absorbed
What are some properties of X-rays?
No charge
No mass
Can travel in a vacuum
Travels at speed of light - 3x10^8 ms^-1
Shorter wavelength and higher frequency than visible light
What is attenuation?
Reduction of intensity of an x-ray beam as it traverses matter.
Reduction may be caused by absorption or deflection (scatter) of photons from the beam.
What are 3 features of a ghost image?
Ghost image can be seen on contralateral side
Ghost image will be horizontally magnified
Ghost image will be superior to actual location
What is collimation?
Restricts the x-ray beam to the area of interest using lead shutters within the X-ray tube
What is the ANODE?
Metal block bombarded with electrons that PRODUCES PHOTONS
Heat produced from electron collisions in target dissipates back into block by thermal conduction
What is the penumbra effect and why does it occur?
Blurring of a radiographic image due to focal spot not being a single point, but rather a small area. (due to omnidirectional x-ray emission) Minimised by shrinking size of focal spot.
Focal spot is where x-rays are coming from. Because beams are coming from different areas why this occurs.
How does rectangular collimation help the patient?
Rectangular collimation is strongly recommended because it can reduce the effective dose to the patient by approximately 50%
What does filtration do?
Filtration removes lower energy (non-diagnostic) x-rays - ones that would be absorbed by patient’s tissues but not contribute to the image
e.g. ones that increase patient dose but NOT increase image quality
ALUMINIUM absorbs these photons
What do X-rays cause in human tissues?
IONISATION - changing overall charge
Displacement/ removal/ adding electrons to an atom.
How can patient dose from X-rays be reduced?
Filtration
Rectangular collimation
Lead shielding
What is rectification and how is it done?
Transforming current from alternating to DIRECT CURRENT.
Direct current is required for x-rays.
TRANSFORMERS - one present at cathode-anode and one present at the filament
What does IRR stand for and who does it protect?
Ionising Radiation Regulations (2017)
Protects staff
What are the 3 IRR principles?
Ensure worker exposure is kept as low as possible
Ensure doses are monitored and recorded
Appropriate training
What does IRMER stand for and who does it protect?
Ionising Radiation Medical Exposure Regulations (2017)
Protects patients
What are the 5 IRMER principles?
Justification - benefit of procedure must outweigh potential risk
Optimisation - radiation dose kept ALARP whilst still providing
Dose Limitation - radiation must be limited to ensure risk of harm is AS LOW AS REASONABLY ACHIEVABLE
Clinical audit
Training
In an OPT, what problem would be seen if the patient tilted their chin down?
Short maxillary teeth, long mandibular teeth
Sometimes overlap of anterior teeth
In an OPT, what problem would be seen if the patient tilted their chin up?
Long maxillary teeth, short mandibular teeth
What would be seen in an OPT if a patient rotated?
Teeth on the side patient rotated to would appear elongated/ stretched.
Teeth on opposite side appear compressed
What would be seen in an OPT if a patient was too far forward?
Anterior teeth appear magnified
Posterior teeth smaller and distorted
Blurry and out of focus
What would be seen in an OPT if a patient was too far back?
Anterior teeth seem smaller/ compressed
Posterior teeth appear larger/ magnified
What size of intra-oral receptors are used for peri-apicals, bitewings and occlusals respectively?
PA - size 0
Bitewing - size 2
Occlusal - size 4
What are some potential causes of a pale image?
Exposure issue - radiation exposure factors too low
Developing issue
- Film removed from solution too early
- Solution too cold
- Solution too dilute/ old
What type of crystals are in FILM?
Silver halide crystals e.g. silver bromide
What does increased film speed lead to?
Leads to less radiation required to achieve image
Affected by number and size of crystals
LARGER crystals = faster film but POORER image quality
What are some advantages of digital radiography over film?
No need for chemical processing
Can be easily transferred to patient notes
Easy storage and archiving of images
Easy back-up of images
Images can be manipulated
What are some disadvantages of digital radiography?
Worse resolution (less pixels)
Risk of data corruption/ loss
Requires diagnostic-level computer monitors for optimal viewing
Image enhancement can create misleading images
