Count statistics of nonparalyzable photon‐counting detectors with nonzero pulse length. Issue 8 (20th July 2018) - Grönberg, Fredrik
Abstract : Purpose: Photon‐counting detectors are expected to be the next big step in the development of medical computed tomography (CT). Accurate modeling of the behavior of photon‐counting detectors in both low and high count rate regimes is important for accurate image reconstruction and detector performance evaluations. The commonly used ideal nonparalyzable (delta pulse) model is built on crude assumptions that make it unsuitable for predicting the behavior of photon‐counting detectors at high count rates. The aim of this work is to present an analytical count statistics model that better describes the behavior of photon‐counting detectors with nonzero pulse length. Methods: An analytical statistical count distribution model for nonparalyzable detectors with nonzero pulse length is derived using tools from statistical analysis. To validate the model, a nonparalyzable photon‐counting detector is simulated using Monte Carlo methods and compared against. Image performance metrics are computed using the Fisher information metric and a comparison between the proposed model, approximations of the proposed model, and those made by the ideal nonparalyzable model is presented and analyzed. Results: It is shown that the presented model agrees well with the results from the Monte Carlo simulation and is stable for varying x‐ray beam qualities. It is also shown that a simple Gaussian approximation of the distribution can be used to accurately model the behavior and performance of nonparalyzable detectors with nonzero pulse length. Furthermore, the comparison of performance metrics show that the proposed model predicts a very different behavior than the ideal nonparalyzable detector model, suggesting that the proposed model can fill an important gap in the understanding of pileup effects. Conclusions: An analytical model for the count statistics of a nonparalyzable photon‐counting detector with nonzero pulse length is presented. The model agrees well with results obtained from Monte Carlo simulations and can be used to improve, speed up and simplify modeling of photon‐counting detectors.