10 - Quality assurance and fault analysis

Question 1

What does the quality assurance programme cover?

Answer 1

• procedures
• staff training
• equipment
• patient dose
• imaging processing
• image quality

Question 2

How often should receptors be checked for quality?

Answer 2

3 months or sooner if required

Question 3

What should be assessed when quality checking receptors?

Answer 3

• receptor itself
• image uniformity
• image quality

Question 4

How do you check the receptor itself for damage?

Answer 4

• any visible damage to casing or wiring
• cleanliness

Question 5

How do you check the receptor for image uniformity?

Answer 5

Exposure to unattenuated beam (ie table surface) and check that image is consistent shade of grey

Question 6

How do you check the receptor for image quality?

Answer 6

Take radiograph of test object and assess resulting image against baseline

Question 7

How do scratches appear on a phosphor plate?

Answer 7

White line

Question 8

How do cracks appear on a phosphor plate?

Answer 8

Network of white lines from flexion

Question 9

How does delamination appear on a phosphor plate?

Answer 9

White areas at edge where phosphor layer has separated from plate

Question 10

How does damage appear on solid state sensors?

Answer 10

White squares or lines from dead pixels

Question 11

How does damage appear on film?

Answer 11

• white scratches if emulsion scraped off
• black marks due to heat or pressure ie fingerprints

Question 12

What is a step wedge?

Answer 12

• test object used to check image quality
• overlapping layers of lead foil attenuate beam in stepwise style
• should be compared to baseline

Question 13

How are clinical radiographs analysed for quality?

Answer 13

• image quality rating (grading)
• image quality analysis (calculate success rate over period of time)
• reject analysis (analyse reason behind unacceptable image)

Question 14

What are the different ratings for radiograph analysis?

Answer 14

• diagnostically acceptable (A)
• diagnostically not acceptable (NA)

Question 15

What is the target for A rated radiographs?

Answer 15

Digital > 95%
Film >90%

Question 16

How do you determine if an image is diagnostically acceptable?

Answer 16

• shows correct teeth?
• shows correct parts of teeth?
• shows relevant surrounding structures?
• shows extent of any pathology?

Question 17

What are the diagnostically acceptable positioning factors for bitewings?

Answer 17

• shows entire crown for upper and lower teeth
• includes distal aspect of canine
• includes mesial aspect of last standing tooth (ok to require more than 1 BW)
• approximate surfaces are shown without overlap

Question 18

What are the diagnostically acceptable positioning factors for periapicals?

Answer 18

• show entire root
• shows periapical bone
• shows crown

Question 19

What are potential faults on images?

Answer 19

• too dark or pale (can be corrected if digital)
• inadequate contrast
• unsharp
• distorted
• over collimated
• receptor damage

Question 20

What is cone cutting?

Answer 20

• incorrect assembly of receptor holder
• incorrect collimator alignment

Question 21

What are causes of images being too light or dark?

Answer 21

• exposure settings incorrect
• developing factors if using film
• viewing factors ie light soucre or inappropriate screen

Question 22

Describe a ghost image.

Answer 22

• appears in position and on contralateral side
• appears distorted
• appears at a different height

Question 23

Why do teeth appear narrow on an OPT?

Answer 23

• teeth are buccal to focal trough
• patient is too far into machine

Question 24

Why do teeth appear wider on an OPT?

Answer 24

• teeth are lingual to focal trough
• patient is too far back in the machine