iaea human health series publications - SEDIM

artefacts are typically best seen while observing the phantom image as a whole, not piecewise. Detailed artefactsare typically best seen while observing the phantom image at full spatial resolution, where one pixel on thedisplay matches one pixel in the image, or even in magnified form (with a magnification greater than 1.0).Record the absence or presence of artefacts on the full field artefacts chart (Chart 10 in Annex I).Note: An artefact is considered significant if it may mimic or obscure anatomic features.(8) Display the uniformity image with a zoom factor that displays full resolution (1:1 pixel mapping). Reduce thewindow width until the texture (noise pattern) becomes apparent. Pan over the entire image, examining theimage for pixels that appear much brighter or darker than the background (referred to as ‘bright’ and ‘dark’pixels, respectively) and for variations in the amount of noise and texture from place to place in the image.The texture of the image should be uniform over the entire image or at least be similar to the baseline. If thisplace to place variation changes over time, areas where there appears to be less noise may indicatedegradation in the detector, causing a loss of sharpness. At the same time, the presence in the image of pixelsthat are substantially brighter or substantially darker than the average should be noted. This may indicate deadelements in, or other degradation of, the detector. Report this finding to the medical physicist and/orradiologist for further investigation and consideration of whether the problem is of a magnitude and naturethat is likely to cause a reduction in diagnostic image quality.(9) If patient images are interpreted on hard copy, print the image using the window width and window level thatwould be used for a patient image. View the image on a mammographic quality viewbox, preferably the oneused by the radiologist. Evaluate the entire phantom image for artefacts, recording the absence or presence ofartefacts on the full field artefacts chart (Chart 10 in Annex I). Record whether the phantom image wasevaluated on hard copy (H), soft copy (S) or both (B).Note: It is not necessary to view the image on all available soft copy monitors. This is a test of imageacquisition, not display. Monitor performance is assessed separately.(10) Repeat steps 1–9 for all clinically used filters and also using fine focus and magnification, if applicable.(11) Record the outcome of the test on the monthly, quarterly and semi-annual checklist (Chart 2 in Annex I).7.3.2.4. Interpretation of results and conclusions(1) There should be no blotches or regions of altered texture appearance.(2) There should be no observable lines or structural artefacts.(3) There should be no ‘bright’ or ‘dark’ pixels evident.7.3.2.5. Recommendations and corrective actionsIf results are unacceptable, the tests should be repeated. If the results remain unacceptable, it may beappropriate to contact the responsible medical physicist for further advice on implementing the recommendationlisted below:If any artefacts are visible that could mimic or obscure anatomical information, or if any patterns are seen, arecalibration or flat fielding of the digital detector is needed. After this has been done, repeat the test. If artefactspersist, contact the authorized service representative.7.3.2.6. Time frame for corrective actionImmediately: If this test fails, do not image patients until corrective action has been taken.67