Quality assurance

Published on 12/06/2015 by admin

Filed under Radiology

Last modified 22/04/2025

Print this page

This article have been viewed 1414 times

11 Quality assurance

Definition of quality assurance

	A method of testing digital imaging systems to ensure consistency of results within the computer network. (See also Appendix F: Quality Assurance and Tests.)
Equipment Required	• 1 mm copper filter • 1 straight edge metal strip • Leeds Tor 18 test tool • Leeds test object N3 • Leeds test object GS2 • Leeds test object T010

Test for low contrast sensitivity and resolution

Equipment Required	• Leeds Tor 18 test object • 1 mm copper filter • 24 × 30 cm cassette • X-ray tube
Equipment Tested	• Viewing stations • Laser printers
Testing Frequency	Weekly
Testing Method	• Test tool is placed in the centre of the cassette • X-ray tube centred to the cassette • Collimators are fully opened • Copper filter placed next to the tube • Expose plate using: 100 cm, 55 kVp, 45 mAs • Process the film
Results	• View the image on the main workstation monitor • The monitor should not be adjusted • 18 discs around the inside edge of the circular image should be seen This gives the grey scale of contrast • The line pairs in the middle of the pattern are counted Note if the lines appear to merge they are not counted This gives the resolution of the system • The test is repeated on the other monitors by the same person • The test is sent to the laser printers and evaluated by the same person
Evaluation	• Using the table for testing fluoroscopic equipment • Acceptable results are: 16 discs seen, 14 line pairs 2.24 spatial frequency cycles per millimetre A difference of 3 or more discs or 3 or more line pairs indicates a problem, but note that a difference of one could be due to the eyesight of the person doing the test If only one monitor shows a different result the problem is with that monitor If all show a different result the cause could be: – The processor – The cassette – The X-ray tube

Phosphor screen check

Equipment Required	• X-ray tube • Cassettes
Equipment Tested	5 random cassettes of different sizes and resolution
Testing Frequency	Weekly
Testing Method	• Cassettes are exposed • Collimators fully opened • Expose plate using: 100 cm, 55 kVp and 6.3 mAs
Results	• Process as usual • View on main workstation monitor
Evaluation	• Look for: Scratches Dirt Artefacts • If any damage is seen the cassette should be replaced

Laser beam function in the processor

Equipment Required	• A straight edged metal strip • 35 × 43 cm cassette
Equipment Tested	Processor laser beam: • Focus • Movement • Scan line alignment
Testing Frequency	• Every 3 months • After every service
Testing Method	• A straight edged metal strip is placed diagonally over the cassette • Expose plate using: 100 cm, 55 kVp and 6.3 mAs
Results	• Process as usual • View on main workstation monitor • View on one other monitor • Print a copy
Evaluation	• The edges of the metal strip should be: Straight Continuous • Wavy edges or gaps indicate Timing problems Laser beam modulation problems

Receptor reproducibility, uniform density, artefact analysis

Equipment Required	2 metal objects to represent artefacts (e.g. paper clips)
Equipment Tested	• Processor • Cassette
Testing Frequency	• Every 3 months • After every service
Testing Method	Metal artefacts are placed on two adjacent corners of the cassette • Expose plate using: 180 cm, 55 kVp and 10 mAs
Results	• Process as usual • View on main workstation monitor • The image should be even
Evaluation	• Black or white areas, streaks Repeat the test with the cassette rotated through 180° • If the artefact has moved sides Check and clean the cassette Repeat the test • If the artefact is on the same side Indicates processor fault Report to service department

Screen cleaning

Equipment Required	Proprietary screen cleaner
Equipment Tested	All cassettes
Frequency	Every 2 weeks
Method	• Only clean screens with the cleaning solution recommended by the manufacturer of the screens • Dust and dirt should be removed with a soft brush, such as a camera lens cleaning brush • For ingrained dirt, use a lint-free cloth and screen cleaner, rubbing in a circular motion without undue pressure • Once the screens have been cleaned, leave the cassettes partially open so the screens can dry naturally
Method	Note Most screen cleaners contain an antistatic element as static will attract dirt and dust

Danson D 2002 Quality assurance for computed radiography. Synergy, April

Digital and Radiographic Imaging A Practical Approach