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Citation:
900.12(e)(5)(viii): Uniformity of screen speed. Uniformity of the screen speed of all the cassettes in the facility shall be tested and the difference between the maximum and minimum optical densities shall not exceed 0.30. Screen artifacts shall also be evaluated during this test.
Discussion:
The intent of this regulation is to provide the technologist performing the examination reasonable assurance that there will be consistency and reproducibility between the images produced using the same type cassette. However, a facility may use cassettes specifically designed to be of different speeds to deal with various clinical problems. In addition, cassettes of different sizes, even from the same manufacturer, may yield different screen speeds due to differences in design and the use of different types of screens. In those cases where a facility has clearly and permanently identified groups of cassettes of different speeds, has established mammographic technique charts to compensate for the different speed cassettes, and has made these charts available to all their radiologic technologists, the facility can group these cassettes for purposes of the screen speed uniformity test. As long as the difference between the maximum and minimum optical density of all cassettes within a group does not exceed 0.30, the requirement has been met. For any group of cassettes used to image the standard breast, the facility must assure that the radiation dose does not exceed the requirement limit of 3.0 milligray (mGy).
Yes.
The screen-film contact and uniformity of screen speed tests must be performed on new cassettes prior to clinical use. 21 C.F.R. 900.12(e)(10). Because the screen-film contact test is a semi-annual QC test, the QC technologist may perform this test. The uniformity of screen speed test, including testing for screen artifacts, is part of the annual physicist’s survey and, in that context, must be performed by the medical physicist. C.F.R. 900.12(e)(5)(viii), (e)(9). However, in the context of cassettes being added during the course of the year (between annual physics surveys), the QC technologist (or someone with adequate training designated by the QC technologist) can perform this test in consultation with the medical physicist. However, in all cases where the newly acquired cassette(s) are nominally of a different speed from the existing group of cassettes [e.g., speed class 100 (regular) for the new cassettes vs. 150 (fast) for the existing cassettes], the medical physicist should provide oversight. If these new cassettes are used to image the standard breast and require higher technique factors such that the dose could reasonably exceed 300 mrad (3.0 mGy), a mean glandular dose measurement must be performed for the new group of cassette(s). In such a case, the medical physicist must perform this dose measurement test before this group of cassettes is used on patients. 21 C.F.R. 900.12(e)(10).
Related Topics:
Annual Equipment Quality Control Tests