BDS3 X-ray physics and other things

Question 1

What is EM radiation?

Answer 1

Movement of energy as photons
Measured in eV

Question 2

What is the difference between gamma radiation and X-rays?

Answer 2

Essentially the same but gamma radiation occurs naturally and X-rays are man-made.

Question 3

How are X-rays produced?

Answer 3

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).

Question 4

What are the types of x-rays?

Answer 4

HARD - higher energies, able to penetrate human tissues - medical imaging mostly uses this
SOFT - lower energies - easily absorbed

Question 5

What are some properties of X-rays?

Answer 5

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

Question 6

What is attenuation?

Answer 6

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.

Question 7

What are 3 features of a ghost image?

Answer 7

Ghost image can be seen on contralateral side
Ghost image will be horizontally magnified
Ghost image will be superior to actual location

Question 8

What is collimation?

Answer 8

Restricts the x-ray beam to the area of interest using lead shutters within the X-ray tube

Question 9

What is the ANODE?

Answer 9

Metal block bombarded with electrons that PRODUCES PHOTONS
Heat produced from electron collisions in target dissipates back into block by thermal conduction

Question 10

What is the penumbra effect and why does it occur?

Answer 10

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.

Question 11

How does rectangular collimation help the patient?

Answer 11

Rectangular collimation is strongly recommended because it can reduce the effective dose to the patient by approximately 50%

Question 12

What does filtration do?

Answer 12

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

Question 13

What do X-rays cause in human tissues?

Answer 13

IONISATION - changing overall charge
Displacement/ removal/ adding electrons to an atom.

Question 14

How can patient dose from X-rays be reduced?

Answer 14

Filtration
Rectangular collimation
Lead shielding

Question 15

What is rectification and how is it done?

Answer 15

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

Question 16

What does IRR stand for and who does it protect?

Answer 16

Ionising Radiation Regulations (2017)
Protects staff

Question 17

What are the 3 IRR principles?

Answer 17

Ensure worker exposure is kept as low as possible
Ensure doses are monitored and recorded
Appropriate training

Question 18

What does IRMER stand for and who does it protect?

Answer 18

Ionising Radiation Medical Exposure Regulations (2017)
Protects patients

Question 19

What are the 5 IRMER principles?

Answer 19

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

Question 20

In an OPT, what problem would be seen if the patient tilted their chin down?

Answer 20

Short maxillary teeth, long mandibular teeth
Sometimes overlap of anterior teeth

Question 21

In an OPT, what problem would be seen if the patient tilted their chin up?

Answer 21

Long maxillary teeth, short mandibular teeth

Question 22

What would be seen in an OPT if a patient rotated?

Answer 22

Teeth on the side patient rotated to would appear elongated/ stretched.
Teeth on opposite side appear compressed

Question 23

What would be seen in an OPT if a patient was too far forward?

Answer 23

Anterior teeth appear magnified
Posterior teeth smaller and distorted
Blurry and out of focus

Question 24

What would be seen in an OPT if a patient was too far back?

Answer 24

Anterior teeth seem smaller/ compressed
Posterior teeth appear larger/ magnified

Question 25

What size of intra-oral receptors are used for peri-apicals, bitewings and occlusals respectively?

Answer 25

PA - size 0
Bitewing - size 2
Occlusal - size 4

Question 26

What are some potential causes of a pale image?

Answer 26

Exposure issue - radiation exposure factors too low

Developing issue
- Film removed from solution too early
- Solution too cold
- Solution too dilute/ old

Question 27

What type of crystals are in FILM?

Answer 27

Silver halide crystals e.g. silver bromide

Question 28

What does increased film speed lead to?

Answer 28

Leads to less radiation required to achieve image

Affected by number and size of crystals
LARGER crystals = faster film but POORER image quality

Question 29

What are some advantages of digital radiography over film?

Answer 29

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

Question 30

What are some disadvantages of digital radiography?

Answer 30

Worse resolution (less pixels)
Risk of data corruption/ loss
Requires diagnostic-level computer monitors for optimal viewing
Image enhancement can create misleading images