IRMER Dose Reduction

Question 1

What are the 3 core principles for protecting pts from radiation?

Answer 1

Justification
Optimisation
Limitation

Question 2

What is justification?

Answer 2

Should be benefit for pt
Should provide new diagnostic info to aid pt management

Question 3

What is optimisation?

Answer 3

Getting it right 1st time, technique
Keeping dosages as low as reasonably possibly ALARP
Reduce retakes

Question 4

What is limitation?

Answer 4

Dose limits should not be exceeded for workers and public
No dose limits for individual pts, justification protects pts from unnecessary exposure

Question 5

What factors affect optimisation?

Answer 5

Equipment factors
Viewing conditions
Technique factors

Question 6

For IO radiography which equipment factors should be considered? (6)

Answer 6

Method of x ray generation
Kilovoltage
Filtration
Collimation
Cone length (focus to skin distance)
Image receptor

Question 7

What makes efficient x ray generation?

Answer 7

Constant potential / DC (direct current) waveform
kV kept at its peak throughout exposure
More high energy useful x ray photons
Less low energy harmful x rays

Question 8

Why is direct current DC favoured over alternating current AC waveform?

Answer 8

AC produces more low energy x rays - harmful
DC produces more high energy x rays, photons used efficiently - useful

Question 9

What kV should new equipment operate at?

Answer 9

60 - 70 kV

Question 10

What is the problem with lower kV?

Answer 10

Photoelectric effect dominates, this is pure absorption - harmful

Question 11

What is the advantages of increasing kV from 50 to 65?

Answer 11

Halves the effective dose
Higher kV lowers the dose (more photons pass through) and lowers the contrast

Question 12

What is the relationship between kV and dose?

Answer 12

As kV increases, dose decreases
After 60 kV the dose plateaus even as kV increases

Question 13

What determines exposure time?

Answer 13

Child / adult / large adult
Anterior / premolar / posterior

Question 14

Define filtration

Answer 14

Removes low energy photons which contribute most to dosage

Question 15

What is filtration level up to and including 70 kV

Answer 15

1.5mm Aluminium

Question 16

What is filtration level above 70 kV

Answer 16

2.5mm Aluminium

Question 17

What shapes and limit beam size?

Answer 17

Collimation

Question 18

When should rectangular collimator be used?

Answer 18

Same shapes:
PA
BWs
Occlusals

Question 19

Rectangular vs circular collimator?

Answer 19

Rectangular collimator reduces dose by 50%

Question 20

What is the advantage of a longer spacer cone?

Answer 20

Improves image quality
Reduces pt dose

Question 21

What should the focal spot to skin distance be with spacer cone?

Answer 21

At least 20cm

Question 22

Where should end of spacer cone be positioned?

Answer 22

As close to pt skin as possible without touching

Question 23

What law is spacer cone length determines by?

Answer 23

Inverse square law

Question 24

What is inverse square law?

Answer 24

Doubling the distance, decreases intensity by factor of 4

Question 25

Which image receptor should be used?

Answer 25

Fastest available

Question 26

Which image receptor should not be used?

Answer 26

D speed or some PSPs (phosphor plate)

Question 27

Between F speed and E speed which is better choice and why?

Answer 27

F speed
20% faster

Question 28

What are the 2 types of digital dental imaging systems?

Answer 28

Phosphor plates (CR computer radiography)
Solid state (DR direct digital radiography)

Question 29

What is the advantage of digital radiography over film systems?

Answer 29

Reduced dose for IO radiography

Question 30

When is a thyroid collar used?

Answer 30

When thyroid gland is unavoidably in the primary beam

Question 31

Why should a protective lead apron never be used on patients?

Answer 31

Protective lead apron protects radio-sensitive organs
But primary beam should never be directed at abdomen

Question 32

What can affect viewing conditions of digital radiograph?

Answer 32

Ambient light

Question 33

What should we reduce to optimise viewing conditions? (3)

Answer 33

Ambient light
Glare
Distracting reflections

Question 34

How can we optimise viewing conditions for film radiographs? (4)

Answer 34

Use light box
Reduce ambient light
Mask the film
Magnify the image

Question 35

What kind of technique errors can occur?

Answer 35

Image receptor bent
Cone cutting
Incorrect positioning of image receptor

Question 36

What technique can be used for PAs to avoid technique errors?

Answer 36

Paralleling PA technique

Question 37

How does paralleling PA technique reduce technique errors?

Answer 37

Image receptor and tooth are parallel and visible through beam aiming device

Shortest possible distance between tooth and image receptor

Collimator/x ray beam perpendicular to image receptor and tooth

Question 38

What can be used in panoramic to avoid technique errors?

Answer 38

Light diaphragms to help position pt correctly
- Ala-tragal line
- Mid-saggital line
- Canine line

Question 39

How can dose be reduced in panoramics?

Answer 39

Using sectionals when both sides not indicated

Question 40

Who does dose limitation not apply to?

Answer 40

Patients

Question 41

What are the 3 sources of staff exposure?

Answer 41

Primary beam
Radiation leakage from tubehead
Scatter from patient

Question 42

How is staff exposure limited? (4)

Answer 42

Equipment maintenance
Follow local rules and enforcement in controlled areas
Never hold image receptor in pt mouth during exposure
Never hold tube head during exposure