Comparison of direct-conversion a-Se and CsI scintillator-based CMOS FFDM/DBT flat-panel detectors using an anthropomorphic breast phantom with embedded microcalcification signals

Digital flat-panel detectors (FPD) used in x-ray breast imaging [full field digital mammography (FFDM) or digital breast tomosynthesis (DBT)] utilize semiconductor-based sensors, which directly convert incident x-ray photons into charge pulses, or scintillator-based sensors which, first, absorb x-rays and then re-radiate the energy in a form of optical light, which is subsequently collected by photodiodes. Direct conversion detectors lack the optical light stage and, hence, potentially allow for better spatial resolution, which can be beneficial for imaging of small signals, like microcalcifications. Some of the recent scintillator detectors use columnar CsI to contain optical photon dispersion, by using total internal reflection inside the columns. In this study we test two detectors, an amorphous Selenium (a-Se) direct-conversion FPD with a pixel size of 85 μm, integrated in a number of FFDM and DBT systems, and a new CsI columnar scintillator detector with a 49.5 μm pixel and CMOS active pixel readout technology. Detectors were evaluated, using 1) linear assessment methods, i.e. modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE); 2) a human observer reader study in which microcalcification signals were detected in FFDM images of an anthropomorphic breast phantom.