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Mobile Units Equipment Quality Control


Referenced from the Policy Guidance Help System:


900.12(e)(7): Mobile Units. The facility shall verify that mammography units used to produce mammograms at more than one location meet the requirements in paragraphs (e)(1) through (e)(6) of this section. In addition, at each examination location, before any examinations are conducted, the facility shall verify satisfactory performance of such units using a test method that establishes the adequacy of the image quality produced by the unit. 


Question 1: Does a mobile unit need to include a film processor?

No. A mobile unit does not need to include a film processor. However, any processor used for films taken by the unit must be identified and is subject to MQSA inspections for verification that the equipment meets quality standards. 

Question 2: What would represent an appropriate method for repeat analysis for my mobile service that consists of several individually certified facilities? Should there be an independent analysis for each facility or a combined analysis for all of my facilities?

The repeat analysis must be facility based and not combined with your other facilities. The analysis must be done at least quarterly, and, if possible include at least 250 examinations. 

Question 3: 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.  

Question 4: We are a mobile facility with a van that does not have on-board processing. We have a film-changing room on the van where we load and unload cassettes with film during the day. When the van returns to our main office, we batch process the films. Do we have to perform a semiannual test for darkroom fog in this film-changing room?

Yes. Since you use a room to load and unload cassettes with film, you must test this room for darkroom fog as well as the darkroom for your processor. Both rooms have the potential to fog films and degrade image quality. 

Question 5: We use FDA’s guidance for mobile facilities where we produce a phantom image after a move of the mobile unit and we monitor the mAs. We then process the phantom image later, prior to processing the mammograms. If we move the mobile unit more than once per week, do we also have to produce a weekly phantom image in addition to the phantom produced after each move?

If you use the mode of operation and/or technique factors used clinically for a standard breast for the phantom images that you produce after each move, you do not have to perform an additional weekly phantom image. However, the image used for the weekly phantom test must be evaluated for all required density measurements in addition to the object scores. 21 C.F.R. 900.12(e)(2).


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