10 - Quality assurance and fault analysis Flashcards
What does the quality assurance programme cover?
- procedures
- staff training
- equipment
- patient dose
- imaging processing
- image quality
How often should receptors be checked for quality?
3 months or sooner if required
What should be assessed when quality checking receptors?
- receptor itself
- image uniformity
- image quality
How do you check the receptor itself for damage?
- any visible damage to casing or wiring
- cleanliness
How do you check the receptor for image uniformity?
Exposure to unattenuated beam (ie table surface) and check that image is consistent shade of grey
How do you check the receptor for image quality?
Take radiograph of test object and assess resulting image against baseline
How do scratches appear on a phosphor plate?
White line
How do cracks appear on a phosphor plate?
Network of white lines from flexion
How does delamination appear on a phosphor plate?
White areas at edge where phosphor layer has separated from plate
How does damage appear on solid state sensors?
White squares or lines from dead pixels
How does damage appear on film?
- white scratches if emulsion scraped off
- black marks due to heat or pressure ie fingerprints
What is a step wedge?
- test object used to check image quality
- overlapping layers of lead foil attenuate beam in stepwise style
- should be compared to baseline
How are clinical radiographs analysed for quality?
- image quality rating (grading)
- image quality analysis (calculate success rate over period of time)
- reject analysis (analyse reason behind unacceptable image)
What are the different ratings for radiograph analysis?
- diagnostically acceptable (A)
- diagnostically not acceptable (NA)
What is the target for A rated radiographs?
Digital > 95%
Film >90%
How do you determine if an image is diagnostically acceptable?
- shows correct teeth?
- shows correct parts of teeth?
- shows relevant surrounding structures?
- shows extent of any pathology?
What are the diagnostically acceptable positioning factors for bitewings?
- 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
What are the diagnostically acceptable positioning factors for periapicals?
- show entire root
- shows periapical bone
- shows crown
What are potential faults on images?
- too dark or pale (can be corrected if digital)
- inadequate contrast
- unsharp
- distorted
- over collimated
- receptor damage
What is cone cutting?
- incorrect assembly of receptor holder
- incorrect collimator alignment
What are causes of images being too light or dark?
- exposure settings incorrect
- developing factors if using film
- viewing factors ie light soucre or inappropriate screen
Describe a ghost image.
- appears in position and on contralateral side
- appears distorted
- appears at a different height
Why do teeth appear narrow on an OPT?
- teeth are buccal to focal trough
- patient is too far into machine
Why do teeth appear wider on an OPT?
- teeth are lingual to focal trough
- patient is too far back in the machine
