iaea human health series publications - SEDIM

FIG. 30. Positioning of bathroom scale to perform compression force measurement.(2) In some systems, the breast thickness indicator is calibrated by the manufacturer, taking into account the tiltof the compression plate. In this case, the actual dimension of the PMMA slabs should allow the paddle to tiltduring testing. Special care should be taken not to compress too much, since when this tilting occurs, thegreater the compression force is, the higher the indicated PMMA thickness will be.(3) Apply a compression force used in the clinical setting (e.g. 80 N). Record the force value. Once the applied forcefor this measurement has been established, the same force should be used for all subsequent measurements.(4) Compare the displayed thickness value with the actual thickness of the slab.(5) On systems where the radiographic factors (automatically selected by the system) depend on the compressedthickness, repeat the measurements in magnification mode.8.3.1.4. Interpretation of results and conclusionsTolerances:(1) Maximum compression force for powered compression: no less than 150 N and no greater than 200 N.(2) Maximum manual compression force: less than 300 N.(3) Displayed value accuracy: ±20 N.(4) Acceptable: Displayed thickness within ±8 mm of slab thickness.(5) Achievable: Displayed thickness within ±5 mm of slab thickness.8.3.1.5. Recommendations and corrective actionIf the measured values from these tests are outside the tolerance, the compression device should be calibratedby a qualified service engineer.8.3.1.6. Time frame for corrective actionIf the force measurement is outside the tolerance, the problem should be corrected immediately, before anyfurther patients are imaged. If the thickness indication is outside the tolerance, the problem should be corrected atthe next regular servicing.85