Breast glandular density in dual-energy contrast-enhanced mammography: Effect of cladding in the calibration procedure

Material decomposition methods can be used to quantify volumetric breast density based on dual-energy mammography images; this is of current interest due to the known association between breast density and breast cancer risk. Contrast-enhancement mammography phantoms have been used to calibrate inverse mapping techniques to obtain glandular density and iodine concentration maps. To apply the method, precise calibration is required. We have investigated the effect of cladding material (1 cm wide PMMA bars) around the phantom to make certain that all the phantom elements are properly exposed to primary and scattered radiation. The calibration accuracy was quantified by the maximum absolute deviation and the root mean square error (RMSE) of the fit to calibration data and evaluated for linear and quadratic models, with and without cladding. Results showed that the addition of cladding improved the fit reducing RMSE by 30% and 38% for glandular tissue and iodine quantification, respectively. The best results were obtained when using a quadratic calibration function and the addition of cladding.