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U.S. Department of Health and Human Services

Radiation-Emitting Products

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Phantom Image - Weekly Equipment Quality Control Tests

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Citation: 

900.12(e)(2)(i),(ii),(iii),(iv): (2) Weekly quality control tests. Facilities with screen-film systems shall perform an image quality evaluation test, using an FDA-approved phantom, at least weekly.

(i) The optical density of the film at the center of an image of a standard FDA-accepted phantom shall be at least 1.20 when exposed under a typical clinical condition.

(ii) The optical density of the film at the center of the phantom image shall not change by more than ±0.20 from the established operating level.

(iii) The phantom image shall achieve at least the minimum score established by the accreditation body and accepted by FDA in accordance with 900.3(d) or 900.4(a)(8).

(iv) The density difference between the background of the phantom and an added test object, used to assess image contrast, shall be measured and shall not vary by more than ±0.05 from the established operating level.

Approved Alternative Standards:

Questions:

  1. The regulations specify a minimum optical density of 1.2 at the center of the phantom image when exposed under typical clinical conditions. Is there an upper limit on this density and why does it have to be measured in the center of the phantom?
  2. What is an acceptable documentation for the phantom image QC? Is a table of values sufficient or should the facility plot the results?
  3. A facility is using more than one type of screen-film combination. Must it perform the QC tests separately for each combination used?
  4. Under what circumstances should I establish a new baseline optical density (OD) operating level?
  5. Should artifacts be subtracted during the evaluation of the weekly phantom QC test and should the fibers, speck groups and masses be charted separately?
  6. Under the regulations can the “added” test object used to perform the image contrast test be placed in positions other than on top of the phantom?
  7. If a weekly QC test is performed every week but not every 7 days, can the facility be cited?
  8. When performing the weekly phantom QC test, should we use film from the box currently being used to produce clinical exams or film from the box used for quality control purposes?
  9. When evaluating the phantom QC test, must the technologist and the physicist adjust the phantom scoring for artifacts?
  10. We perform our weekly phantom images using an AEC mode different from the Full-Auto AEC mode that we typically use for patients. Is this acceptable toward meeting the requirement?
  11. When performing the weekly phantom image test must we monitor kVp and/or mAs?
  12. If the optical density (OD) for the weekly phantom test falls below 1.20 (and/or changes by more than +/- 0.20 from the established operating level), must the unit be recalibrated or can we adjust the density setting to obtain a 1.20 OD?
  13. Must the weekly phantom test be performed for all image receptor sizes?
  14. Must the interpreting physician evaluate the weekly phantom QC test?
  15. We use the BACE mode in our Bennett machine to image our patients with the standard breast. In this mode the unit automatically determines the exposure technique factors based on the thickness of the compressed breast. During normal clinical use, the breast compresses and the system provides accurate thickness readings and technique factors. However, when we use this mode (as required by the regulations) for the weekly phantom test, we do not compress the phantom (to avoid damaging the paddle or the phantom) leading to inaccurate thickness readings. These inaccurate thickness readings may cause the unit to select inappropriate exposure technique factors. Can we manually adjust the scale to the thickness of the standard breast before we expose the phantom using the BACE mode? Given the situation described above, is it permissible to expose the phantom using the AEC (see Phantom Images Exposed in Fully Automatic Mode if that is the Clinically Used Technique), rather than the BACE mode?
  16. Our facility has permanently glued the acrylic contrast disk to the phantom at the center of the cover plate. The regulation states that the OD be measured at the center of the phantom which would require our repositioning the disk (which may leave permanent artifacts) or replacement of the phantom cover. Is there another way to leave the disk in place and still fulfill the requirement?
  17. What is considered adequate weekly phantom QC monitoring for a facility that has multiple processors and multiple units?
  18. We are using an FDA cleared single-use cushion pad when performing mammograms on some of our patients. Do we have to include the pad when performing the phantom and dose QC tests?