Finding the best photoconductor for digital mammography detectors

A cascaded model of the spatial-frequency-dependent detective quantum efficiency (DQE) was developed for various photoconductor materials for use in mammography. The model uses Monte Carlo calculations of the absorbed energy distributions for each material and, after experimental validation for an amorphous selenium (a-Se) detector, was used to predict the potential performance of each material. We show that all materials can have a modulation-transfer function value greater than 0.75 at frequencies up to 30 cycles mm−1 and a DQE value greater than 0.2 at frequencies up to 10 cycles mm−1. As such, all materials have good potential for this application. The quantum-noise-limited exposure level determines the ability of each detector material to operate at low exposure levels. It is shown that a-Se detectors have the highest limit (0.01 mR), which is still likely to be low enough for mammography.