iaea human health series publications - SEDIM

8.5. DETECTOR PERFORMANCE8.5.1. Baseline detector performance8.5.1.1. ScopeStrictly speaking, this is not a QC test, but it is required to provide baseline data to be used for subsequenttesting of the detector.— Objective: To establish baselines for the response and noise characteristics of the image acquisition systemunder standard radiation exposure conditions. The test will be performed rarely, but the data sheet producedshould be kept as a reference to be compared against future measurements described in Section 8.5.2.— Minimum frequency: At equipment commissioning and after replacement of the detector.8.5.1.2. Instrumentation(1) PMMA slab(s) of a total thickness of 45 mm.(2) Either the aluminium or the PMMA contrast object used for SDNR measurements.(3) Acquisition or radiologist workstation with ROI capability or QC software for image analysis. Alternatively,images may be downloaded to another computer and analysed using image analysis software.8.5.1.3. MethodologyCR systems should be set to the modes listed in Table 11, and the applicable EIs should be recorded asdescribed in that table. 14Note: These tests should be performed on flat fielded 14 , but unenhanced (‘for processing’) images(i.e. without peripheral or resolution enhancement). For example, GE Fineview TM must be turned off.(1) Create a ‘patient’ study with an appropriate name.(2) Place the 45 mm thick PMMA slab on the tabletop with its long edge aligned with the chest wall edge of thebreast support. Use collimation that allows the full detector area to be exposed.(3) Place the contrast object on the upper surface of the PMMA in the location shown in Fig. 24.(4) Lower the compression plate so that it is in contact with the PMMA.(5) In AEC mode, with the radiographic grid in place, obtain an exposure and record the technique factors on thedetector baseline performance chart (Chart 4 in Annex II).(6) In manual mode (with the radiographic grid in place), obtain an image with the same target–filter and kVselected by the AEC in step 5. Select the closest mAs value available for manual exposure; this is mAs ref .(7) Also obtain images with three additional mAs values that cover the largest practical range spanning the rangeof reasonable mAs settings, for example, values that are one eighth and one half of, and 4 times as large as,mAs ref . Once selected, these settings should be used for all future tests. These images will be used tocharacterize the detector response. For ease of analysis, ensure that the laterality (left or right breast) chosenfor all images is the same, so that the chest wall edge will appear on the same side of the monitor in all images.(8) For CR systems, wait one minute before processing.(9) The air kerma at the entrance to the 45 mm thick PMMA phantom that would result from exposures at thefour mAs values used is determined using the method described in Section 8.7.2 and should be recorded onthe detector baseline performance chart (Chart 4 in Annex II).14Not applicable to CR images.93