Editing Archive (section)

===Corrections for Ring Artifacts and Filter Use===
''email, forwarded from Alexander Sasov, sasov@skyscan.be''
# <U>If ring artifacts appear only when you scan with a filter, you should acquire new flat-field reference for that particular filter and save it. Possible reasons for the rings are switching to another voltage or current or exposure, some particles in the filter surface, cracks or just small changes in the x-ray spectrum of the source, which normally appear in several years of usage.</U>
# Normally one should acquire new flat-field references t wice per year or in the case of the appearance of strong ring artifacts. Another reason to acquire new flat-field references is a system operation with new voltage/current/exposure. Don't forget to save new flat-field references directly after acquisition.