A Monte Carlo method to assess the spectral performance of photon counting detectors.

BACKGROUND: Assessing the performance of spectral detectors is an important but nontrivial problem. In the past few years, detective quantum efficiency-(DQE)-like quantities have been proposed that allow quantifying the spatial-spectral performance for certain tasks. In previous publications, we have presented and validated an approach to determine detector properties like the modulation transfer function (MTF), the noise power spectrum (NPS), and the DQE based on an end-to-end Monte Carlo model of the detection process. This approach has so far not been used to assess the task-dependent spatial-spectral performance of detectors. PURPOSE: In this paper, we extend the Monte Carlo method to detectors with several spectral thresholds and show how it can be used to derive all relevant quantities for the assessment of the spectral performance of such detectors. We describe the method in detail and apply it to four interesting types of realistic detectors. METHOD: The method is an extension of the Monte Carlo method presented previously. An end-to-end Monte Carlo simulation of the detection process directly provides the statistics necessary to obtain all relevant performance parameters, including task-based spectral DQEs. The method is applied to two direct converting photon counting detectors using CdTe and silicon: a CdTe-based photon counter with additional coincidence counters and an optical counting system using LaBr as a scintillator. RESULTS: The task-dependent DQEs show an advantage for CdTe, particularly for non-spectral tasks. Silicon has an advantage for material decomposition tasks at lower frequencies. Both hypothetical systems, the CdTe detector with coincidence counters and the scintillator-based detector, show the potential to outperform the two so-far-realized systems. CONCLUSION: The method presented is a direct method to obtain all relevant quantities (MTF, NPS, various spectral DQEs) from an end-to-end Monte Carlo simulation of the detector. It allows for assessing detector systems currently being used and potential novel detector systems.