Spatio-temporal Monte Carlo modeling of a-Se detectors for breast imaging: Energy-weighted Swank noise and detective quantum efficiency

We study the effect of energy weighting in Swank noise and Detective Quantum Efficiency (DQE) at zero spatial frequency with a detailed Monte Carlo (MC) transport code that includes the three-dimensional spatial and temporal transport of electron-hole pairs in semiconductor x-ray detectors. The transport model takes into account recombination and trapping of carriers including effects of Coulomb forces and external applied electric field. We report pulse-height spectra (PHS) for mono-energetic x rays from 6 to 28 keV photon energy with 0.5 keV step size, and for clinical mammography spectra. A first-approximation electronic noise model is included in the simulations. The Swank calculations take into account the entire PHS distribution while the DQE(0) is calculated from the simulated Swank factor, and quantum efficiency values from the PENELOPE database of attenuation coefficients. The simulated DQE(0) is based on the entire clinical x-ray spectrum and takes into account the energy distribution following Tapiovaara and Wagner's (Phys. Med. Biol. 30, 1985) description for the weighting of carrier transport processes. Swank and DQE simulations for semiconductor detectors can provide insight into the fundamental limitations and possible optimization of breast imaging systems.