Photon-counting detector simulation: Monte-Carlo energy deposition, physics-based charge transport and current induction, and SPICE electronics

Photon counting detectors are an appealing approach to spectral computed tomography for their theoretical benefits over conventional detectors. Detailed modeling and simulation is important for capturing the critical aspects of the counting and spectral performance of the detector. An approach to photon counting detector simulation is presented using a custom developed software program. The software consists of Monte-Carlo energy deposition, physics-based charge transport and current induction, and SPICE electronic simulation. It utilizes behind-the-scenes Gate for the photon interactions and energy deposition and ngspice for the SPICE electronic simulations. Various sensor geometries and definitions can be defined to simulation individual detector pixels or entire anode arrays for large-scale simulations. The simulation requires the specification of x-ray planar sources and can be specified on a per-channel basis with an energy distribution and flux. Given a sensor definition and a series of x-ray sources, the program calculates the energy-bin count read-out from each anode in the sensor array. The program can be used to study the detector response of various sensor and system geometries, including in the presence of anti-scatter grids, the performance of anti-charge sharing implementations, material decomposition algorithms, etc.