How does a facility demonstrate satisfactory performance for mobile units after they are moved to a new location?
For those facilities with mobile units, each mammography unit must be tested after moving to a new examination location and before examining any patients to verify the adequacy of the image quality produced by each unit.
As an example of an acceptable test, a phantom image can be taken in the AEC mode (or the mode used clinically) after the move but prior to patient examination. This image is then either processed and evaluated at the mobile unit site (if possible), or processed off-site and evaluated to verify performance prior to examining patients. A passing object score for this phantom image will be accepted as evidence that the unit is performing adequately after the move and before patient examination.
Another example, for use when processing is not immediately available, is to (1) for a given kVp, record the mAs resulting from a phantom exposure (in the AEC mode under typical clinical conditions or the mode used clinically); (2) compare that mAs to a standard mAs value previously established as ensuring output consistency; and (3) if the two readings are within +/- 10%, proceed with clinical examinations; otherwise take corrective actions to bring the two values within this limit before proceeding with clinical examinations. A crucial follow-up to this test by the facility is to process (using a processor in control) and score the objects in the phantom image taken in step (1) at the earliest time available and before batch processing any of the clinical images. If this phantom image score fails because of any processing problems, the problems should be corrected prior to processing any of the clinical images. If the phantom image score fails due to a non-processor problem, the mobile facility should still process all the films. Each clinical exam should be evaluated individually to determine whether any of the patients have to be recalled to have their images repeated. The entire imaging chain must be checked and adjusted or repaired prior to further clinical use.
If the facility takes a phantom image as part of its post-move/pre-examination testing, it needs to document the object score of the phantom image. The facility needs to keep the written records of post-move/pre-examination tests for the last 12 months or since the last inspection, whichever is longer, and the phantom images for the last 30 days.
Other tests designed by qualified personnel (the medical physicist should be consulted) could be acceptable but may have to be evaluated by the inspector on a case-by-case basis.