The statistics of photon counting detectors (PCDs) differ in several aspects from the statistics of energy integrating detectors (EIDs). Particularly, the effect of crosstalk in a PCD involves a 0/1 decision: a photon may be counted in a neighboring pixel or not whereas in an EID the neighboring pixel may just receive a fraction of the signal. Another interesting effect is that, especially for high counting thresholds, there exists a zone at the edge of the pixel where absorbed x-ray energy will not produce any signal. This may lead to a modulation transfer function (MTF) exceeding the theoretical limit given by the nominal pixel aperture. This fact has also been observed in measurements. Goal of this work is to present a simple but comprehensive description of PCD detectors in the low flux limit capable of including all relevant effects. The model presented is based on a Monte Carlo simulation of the x-ray energy deposition in the detector and a simple model of the charge cloud propagation. A reformulation of the probability generating function formalism allows calculating all relevant quantities like mean signal values or covariances between thresholds and/or neighboring pixels or the MTF and DQE as a function of input photon energy directly from the Monte Carlo simulation.

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Karl Stierstorfer, Martin Hupfer, and Niko Köster, "A simple Monte Carlo model for the statistics of photon counting detectors," Proc. SPIE 10948, Medical Imaging 2019: Physics of Medical Imaging, 109480D (Presented at SPIE Medical Imaging: February 17, 2019; Published: 1 March 2019); https://doi.org/10.1117/12.2504589.