Spatial Resolution Characteristics of A-Se Imaging Detectors Using Monte Carlo Methods with Detailed Spatiotemporal Transport of X-Rays, Electrons, and Electron-Hole Pairs under Applied Bias

Detectability of microcalcifications and small lesions in mammography has driven the development of high spatial resolution imagers with small pixel pitch. In this work, we study the detector resolution limits of amorphous selenium (a-Se) with a detailed Monte Carlo transport code for simulation of direct x-ray detectors. The model takes into account generation and re-absorption of characteristic x rays, spreading due to Compton scattering and high-energy secondary electron transport, and drift and diffusion of electron-hole pairs under the applied external electric field. The transport of electron-hole pairs is achieved with a spatiotemporal model that accounts for recombination and trapping of carriers and Coulombic effects of 3D spatial charge distribution. The location information for each detected electron and hole over millions of simulation histories are used to build the detector point response. A range of incident x-ray energies are simulated from 10 to 100 keV. The simulated detector point response can be used to study the spatial resolution characteristics of detectors at different energies ranges and for calculation of the modulation transfer function and image quality metrics.