H - Radiology

Question 1

What are the 3 basic principles of exposures that must be considered?

Answer 1

Justified - Is there sufficient benefit to offset any detriment caused by x-ray exposure.
Optimised - ALARP (as low as reasonably practical)
Limited - Radiation dose limits applied

Question 2

How do you combat undesirable magnification in paralleling technique?

Answer 2

use long fds (focus to skin distance)

Question 3

What is binding energy?

Answer 3

The amount of energy required to remove an electron from its shell.

Question 4

If you double the distance from x-ray source? what happens to the dosage levels?

Answer 4

Double distance - 1/4 dose

Question 5

What is attenuation?

Answer 5

Reduction in the number of photons
Occurs due to scattering and absorption
partial attenuation grey
complete attenuation white

Question 6

What kV is chosen for intra-orals and why?

Answer 6

60-70kV

Compromises between patient dose and image quality

Question 7

What is an absorbed and equivalent dose?

Answer 7

Absorbed - energy deposited by radiation (Gy)

Equivalent dose - Absorbed dose x weighting factor (depending on type of radiation) X-ray WF = 1

Question 8

Format of digital x-ray images?

Answer 8

DICOM

Question 9

5 steps in film processing?

Answer 9

DWFWD
Developing 
washing 
fixing 
washing 
Drying

Question 10

How to affect film speed?

Answer 10

Number and size of halide crystals
Faster image with larger crystals
However, poorer image quality

Question 11

What are some developing issues and fixing issues?

Answer 11

Developing
- image too light or too dark
Fixing
- brown or yellow image

Question 12

How to use the parallax technique?

Answer 12

Take 2 radiographs to determine if a superimposed structure is lingual or buccal to the reference point.
PAL - if it’s palatal or lingual it will follow the beam of the radiograph.
For example, if you are looking for ectopic canines and take OPT and maxillary occlusal. If the canine is now closer to the apex in the MO then it’s palatally placed.

Question 13

Image quality grades?

Answer 13

Grade 1 - excellent
Grade 2 - diagnostically acceptable
Grade 3 - unacceptable

Question 14

Electrical requirements for an x-ray unit?

Answer 14

Direct current
2 voltages - one high one low
Two transformers - set up across tube and step down across the filament

Question 15

Limitations of OPT?

Answer 15

Patients occlusions e.g class lll
Long exposure time, needs to cope
movement
broad shoulder

Question 16

head position for oblique occlusal? mand + maxilla

Answer 16

Maxilla - horizontal to the ala-tragus line

Mandible - Corner of the mouth-tragus line horizontal

Question 17

The angle of beam for OPT?

Answer 17

8 degrees upwards

Question 18

Head positioning for true occlusal?

Answer 18

Head tipped back as far as possible

Beam at 90 degrees to the image receptor(i.e approaching from under the chin)

Question 19

What is the ideal projection geometry?

Answer 19

Image receptor + Object parallel + in contact

X-ray perpendicular to both

Question 20

What is the bisecting angle technique?

Answer 20

This is used in oblique occlusal to prevent magnification
image + receptor partly in contact, not parallel
X-ray beam at 90 degrees to the line bisecting the angle between tooth and receptor

Question 21

Indications for an occlusal radiograph?

Answer 21

Peri-apical not possible
Pathology too large for peri-apical
Trauma

Question 22

What are IRR17 and IRMER17?

Answer 22

Ionising radiation regulations which deal with occupational exposures and the general public
Ionising radiation medical exposure regulations
- deals with patient exposures

Question 23

Size of films for intra-orals?
Anterior PA 
Posterior PA
Bitewing 
Occlusal

Answer 23

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

Question 24

What are the two occlusal plane curves?

Answer 24

The curve of spee - A-P

The curve of mansion - B-L

Question 25

Cause of horizontal magnification of anterior teeth in an OPT?

Answer 25

Patient too far back in the machine

To close to the X-ray source

Question 26

What does KvP stand for?

Answer 26

Peak kilovoltage