Grönberg Fredrik, Danielsson Mats, Sjölin Martin
Department of Physics, KTH Royal Institute of Technology, AlbaNova University Center, SE-106 91, Stockholm, Sweden.
Med Phys. 2018 Jun 25. doi: 10.1002/mp.13063.
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.
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.
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.
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.
光子计数探测器有望成为医学计算机断层扫描（CT）发展的下一个重大进展。在低计数率和高计数率情况下对光子计数探测器的行为进行准确建模，对于准确的图像重建和探测器性能评估至关重要。常用的理想非可加性（δ脉冲）模型基于粗略的假设构建，使其不适用于预测高计数率下光子计数探测器的行为。这项工作的目的是提出一种分析计数统计模型，该模型能更好地描述具有非零脉冲长度的光子计数探测器的行为。
使用统计分析工具推导了具有非零脉冲长度的非可加性探测器的分析统计计数分布模型。为了验证该模型，使用蒙特卡罗方法模拟了一个非可加性光子计数探测器并进行比较。使用费希尔信息度量计算图像性能指标，并给出并分析了所提出模型、所提出模型的近似值以及理想非可加性模型所做近似值之间的比较。
结果表明，所提出的模型与蒙特卡罗模拟结果吻合良好，并且对于不同的X射线束质量是稳定的。还表明，该分布的简单高斯近似可用于准确模拟具有非零脉冲长度的非可加性探测器的行为和性能。此外，性能指标的比较表明，所提出的模型预测的行为与理想非可加性探测器模型非常不同，这表明所提出的模型可以填补在理解堆积效应方面的一个重要空白。
提出了一种具有非零脉冲长度的非可加性光子计数探测器的计数统计分析模型。该模型与蒙特卡罗模拟获得的结果吻合良好，可用于改进、加速和简化光子计数探测器的建模。
