Radiology

Question 1

Radiation protection

1. 3 principles of radiation protection – define, how achieved
2. IRMER regulations
3. Image receptors colours
4. Risk categories

Answer 1

1. Justification - any exposure must benefit patient/provide new information for diagnosis/treatment planning
   Optimisation - must be ALARP
   Dose limitation - for radiation workers and members of public. Achieved via rectangular collimation, high KVp, rare-earth screens, digital/fast film speed
2. Employer, referrer, practitioner (authorisation, justification, optimisation), operator (dose radiation)
3. Blue - anterior PA
   Yellow - posterior PA
   Red - BW
   Green - endo
4. High risk - every 6mths
   Moderate risk - every 12mths
   Low risk - every 24mths (12-18mths for primary dentition)

Question 2

Define radiographic image

Answer 2

Pictorial representation of a part of the body. Record of the pattern of attenuation of the x-ray beam after it has passed through matter

Question 3

Techniques

1. 2 PAs
2. BW

Answer 3

1. Paralleling - image receptor and object parallel but not in contact. Some distance apart, so long fsd used to reduce magnification
   Bisecting angle - image receptor and object in partial contact but not parallel. Beam 90 degrees to bisceting line, halfway between long axis of tooth and plane of image receptor
2. Image receptor parallel to line of arch. Front edge of film packed mesial to 3/4 contact. collimation, tube head alignment

Question 4

OPT

1. 2 reasons
2. 2 cons
3. Technique (lining up patient, etc.)

Answer 4

1. Trauma, development of dentition, can’t tolerate IO x-ray
2. Increased exposure time, positioning difficulties
3. MS plane centred, FP horizontal (parallel to floor). vertical canine line shines on U3, hold handles, bite on bite block, tongue to palate, no jewellery/dentures

Question 5

Focal trough

1. Define
2. 2 factors it depends on
3. Why do positioning faults occur (why are there different layer position speeds)
4. How are positioning faults prevented
5. Why OPT stretched/maginfied horizontally
6. 3 features of ghost images

Answer 5

1. Layer in patient containing structures of interest, demonstrated with sufficient resolution to be recognisable
2. Distance from rotation centre, x-ray beam width
3. Posterior teeth are further from rotation centre (closer to x-ray source) = faster beam and image receptor
4. Synchronising
5. Canines behind vertical canine line (too close to x-ray source), and not corrected
6. Reflected onto opposing side of image (absorb remaining x-ray beam before it reaches image receptor after passing through opposing side), always horizontally magnified, approx. 8 degrees higher, can interfere with diagnosis

Question 6

Quality assurance

1. 3 grades
2. Describe coin/safelight test description

Answer 6

1. Grade 1 - excellent (>70%)
   Grade 2 - diagnostically acceptable (<20%)
   Grade 3 - unacceptable (<10%)
2. In the dark, place coins at specific intervals on an EO film and cover, turn safelight on, uncover coins at specified (10s/30s) intervals leaving last one covered, process, identify what can be seen

Question 7

X-ray production – describe

Answer 7

X-rays are produced by the rapid deceleration of electrons.
Electrons fired at atoms at high speed and collide (lower electron speeds), releasing kinetic energy, which is converted into EM radiation (x-rays) and heat. X-ray photon is the aimed at subject

Question 8

3 components of tubehead and function

Answer 8

Filament - provides current for x-ray production
Target - focal spot
Lead - shielding
Aluminium - filtration
Rectangular collimator - reduce scatter, reduce area irradiated
Spacer cone - controls target fsd

Question 9

3 types of attenuation and appearance/colour

Answer 9

No attenuation - black - pass through unaltered
Partial - grey - absorbed and scattered (partially absorbed)
Complete - white - complete absorption, electron energy lost in tissues

Question 10

Tissue interactions 1

1. Describe photoelectric effect
2. What makes a photon more likely to be absorbed
3. Effect on dose and image quality

Answer 10

1. Low energy phenomenon. Photon interacts with inner shell electron and so the photon energy is just greater than the electron binding energy. Photon energy used to eject electron. Atom rearranges, releasing energy as characteristic spectrum radiation. Outer void filled by colliding photon (as it has delivered its total energy to a single electron and is completely absorbed)
2. Lower/reduced energy, thicker/denser tissue/object
3. Increase in dose and increase in image quality

Question 11

Tissue interactions 2

1. Describe Compton scatter
2. Describe effect of Compton scatter
3. 2 ways it is reduced
4. What affects the probability of Compton scatter occurring
5. Effect on dose and image quality

Answer 11

1. Mid energy phenomenon. Photon interacts with loosely bound electron and so the photon energy is much greater than the electron binding energy. Photon collides with electron, ejecting it. Atom rearranges, releasing energy as continuous spectrum radiation. Outer void filled by free electron capture. During collision, the photon loses some of its energy (decelerated) and is deflected/scattered (recoil electron), free to interact with other atoms.
2. Photons scattered backwards after the image receptor may reach the image receptor and contribute to a darker image
3. Collimation and lead foil lining packets
4. Electron density
5. Increase in dose, no increase in quality

Question 12

Absorbed dose

1. Define
2. How reduced

Answer 12

1. Energy impaired by radiation to unit mass of tissue

2. High kVp (higher energy photons, less absorbed)

Question 13

Digital

1. 3 benefits
2. 2 cons
3. 2 types and describe differences
4. 4 image receptor sizes

Answer 13

1. Image enhancement, instant image production, dose reduction, constant quality, no chemicals/processing
2. Expensive, large size of image receptors, expensive
3. CCD - image detected on photomultiplier. Direct link to computer, active area smaller than film
   PSP - latent image stored after x-ray exposure, transferred from sealed packet, laser scanning, light emission, electronic signal. Flexible plate, variable light sensitivity
4. Size 0 - 21x34mm
   Size 1 - 24x40mm
   Size 2 - 30x40mm
   Size 4 - 57x75mm

Question 14

Lat ceph

1. 3 EO reference lines
2. Define
3. Why reproducible
4. 2 indications
5. Technique

Answer 14

1. MS reference line/plane, FP, pupillary line, OM line
2. Standardised and reproducible true lateral view of facial bones, base of skull and upper C-spine. Also shows sinus and soft tissues
3. Patient positioned in cephalostat, a set distance (5ft) from x-ray source
4. Ortho patients, patients with AP/vertical discrepancies, monitor and track growth
5. X-ray tube head and cephalostat lined up with image receptor, thyroid collar, FP horizontal, MS plane vertical and 5ft from source, centric occlusion, ear rods in EAM, nation support, magnification scale in image

Question 15

X-ray film

1. Function of lead foil
2. What speeds
3. Function of intensifying screen
4. Processing chemical process stages
5. Why image darker

Answer 15

1. Absorbed scatter x-rays, preventing image degredation
2. E or faster (E is 2x faster than D; F shows 20% does reduces vs. E)
3. Fewer photons, reduce dose reduction (and image quality)
4. Development, rinse, fixation, wash, dry
5. Increased time, temperature, concentration

Question 16

Localisation

1. 2 indication
2. Important requirements
3. Parallax definition

Answer 16

1. Unerupted tooth position, trauma, root/canal location
2. Stable reference point, horizontal/vertical tube shift (for non-right-angle views)
3. Apparent change in position of object caused by real change in position of observer