Use of the European Protocol to Optimise a Digital Mammography System
An experimental method of determining the optimal beam qualities and doses for digital mammography systems is described, and applied to a CR system. The mean glandular dose (MGD) and contrast-to-noise ratio (CNR) were measured using phantoms. For each thickness of phantom a range of kV and target/filter combinations were tested. Optimal beam quality was defined as that giving a target CNR for the lowest MGD. The target CNR was that necessary to achieve at least the minimum standard of image quality defined in European Guidance. An inverse relationship between CNR and threshold contrast was confirmed over a range of thicknesses of PMMA and different beam qualities and doses. Optimisation indicated that relatively high energy beam qualities (e.g. 31 kV Rh/Rh) should be used with a greater detector dose to compensate for the lower contrast when compared to using lower energy X-rays. The results also indicate that current AEC designs that aim for a fixed detector dose are not optimal.
KeywordsBeam Quality Digital Mammography Compute Radiography Threshold Contrast Automatic Exposure Control
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