Quantification of scattered radiation in projection mammography:Four practical methods compared

Four different practical methodologies of quantifying scattered radiation for two different digital mammographic systems are compared. The study considered both grid in and grid out geometries. The aim was to find quick and reproducible methods that could be used in place of the beam stop technique.The four scatter estimation methods applied were (1) the beam stop (BS) method, (2) a hybrid method that combined measured detector (scatter-free) modulation transfer function (MTF) data and a Monte Carlo simulation of the scatter point spread function, (3) from the low frequency drop data taken from the system MTF, and (4) from the edge spread function (ESF) measured in the presence of PMMA. In conclusion all alternative methods to the BS technique gave reasonable estimates of SPR without grid, with a maximum difference of 24% (mean difference 8%). For the grid in geometry, the direct MTF method gave a maximum difference of 24% for the linear grid system, while maximum percentage difference was 119% (absolute difference of 0.042) for the system with the cellular grid, where SPR values were low. Except for cases where the SPR is very low, the direct MTF method offers a quick and reproducible alternative to the BS technique.