iaea human health series publications - SEDIM

8.4.2. AEC evaluation8.4.2.1. Scope— Objective: To evaluate the ability of the system to image a clinically expected range of breast thicknesses andto ensure that images of adequate penetration and acceptable SDNR levels are produced; to determine theimaging technique factors required for the estimation of MGD.— Frequency: Annually and when updates or changes have been made to AEC control software.8.4.2.2. Instrumentation(1) Three slabs of PMMA: one 20 mm thick and two 25 mm thick. A semicircle 18–20 cm in diameter is theoptimum phantom so that AEC systems with breast edge detection operate properly. For other systems,uniform slabs of at least 18 cm × 24 cm 10 will enable artefact analysis as well.(2) Contrast object. This can be a 1 mm thick, 25 mm diameter depression in the PMMA slab (the depressionmust have a flat, smooth bottom); a 1 mm thick, 25 mm diameter PMMA disc; or a 0.2 mm thick square ofaluminium, 10 mm on a side.(3) Appropriate spacers (e.g. radiolucent U shaped rigid expanded polystyrene of the thicknesses given inTable 12, to set the compression paddle position). These spacers are required to simulate breast thicknessesfor dosimetry purposes and to test the AEC (45 mm of PMMA plus an 8 mm spacer simulates a ‘standard’breast, 53 mm thick, while a 70 mm thick PMMA disc plus a 20 mm thick spacer simulates a 90 mm thick‘large’ breast of typical composition [48]).8.4.2.3. MethodologyFor all tests of CR systems, the systems should be set to the modes indicated in Table 11 and the applicableEIs given in that table should be recorded.(a)Thickness behaviour(1) Create a ‘physics’ study with an appropriate name, with the images saved in a ‘for processing’ format. Anypre-processing algorithm other than flat field or shading (e.g. Fineview ΤΜ on GE systems) should be turnedoff, if this is possible. It is important that the acquired image be saved in a ‘raw’, ‘unprocessed’ or DICOM‘for processing’ format. It may be necessary to close the study used for acquiring other images and open anew one after turning off pre-processing.TABLE 12. SPACER THICKNESS REQUIRED TO MATCH PMMA THICKNESS TO A BREAST OFEQUIVALENT THICKNESSBreast typeEquivalent breast thickness(mm)PMMA thickness(mm)Spacer thickness(mm)Thin 21 20 0Standard 53 45 8Thick 90 70 2010For the artefact test (see Section 8.5.5), one of these slabs should be large enough to cover the entire area of the detector.Alternatively, a slab provided by the equipment manufacturer can be used for this purpose.88