Siemens Healthcare, Siemensstr. 3, Forchheim, 91301, Germany.
Med Phys. 2018 Jan;45(1):156-166. doi: 10.1002/mp.12667. Epub 2017 Dec 5.
To find a simple model for the frequency-dependent detective quantum efficiency (DQE) of photon-counting detectors in the low flux limit.
Formula for the spatial cross-talk, the noise power spectrum and the DQE of a photon-counting detector working at a given threshold are derived. Parameters are probabilities for types of events like single counts in the central pixel, double counts in the central pixel and a neighboring pixel or single count in a neighboring pixel only. These probabilities can be derived in a simple model by extensive use of Monte Carlo techniques: The Monte Carlo x-ray propagation program MOCASSIM is used to simulate the energy deposition from the x-rays in the detector material. A simple charge cloud model using Gaussian clouds of fixed width is used for the propagation of the electric charge generated by the primary interactions. Both stages are combined in a Monte Carlo simulation randomizing the location of impact which finally produces the required probabilities. The parameters of the charge cloud model are fitted to the spectral response to a polychromatic spectrum measured with our prototype detector.
Based on the Monte Carlo model, the DQE of photon-counting detectors as a function of spatial frequency is calculated for various pixel sizes, photon energies, and thresholds.
The frequency-dependent DQE of a photon-counting detector in the low flux limit can be described with an equation containing only a small set of probabilities as input. Estimates for the probabilities can be derived from a simple model of the detector physics.
在低流量极限下，找到一种用于光子计数探测器频率相关探测量子效率（DQE）的简单模型。
推导了在给定阈值下工作的光子计数探测器的空间串扰、噪声功率谱和 DQE 的公式。参数是中央像素中单计数、中央像素和相邻像素的双计数或仅相邻像素中单计数等事件类型的概率。这些概率可以通过广泛使用蒙特卡罗技术在简单模型中推导出：使用蒙特卡罗 X 射线传播程序 MOCASSIM 模拟探测器材料中 X 射线的能量沉积。使用具有固定宽度的高斯云的简单电荷云模型用于传播由初级相互作用产生的电荷。这两个阶段在蒙特卡罗模拟中组合在一起，随机化撞击位置，最终产生所需的概率。电荷云模型的参数拟合到我们的原型探测器测量的多色光谱的光谱响应。
基于蒙特卡罗模型，针对各种像素大小、光子能量和阈值，计算了光子计数探测器的 DQE 作为空间频率的函数。
在低流量极限下，光子计数探测器的频率相关 DQE 可以用仅包含少量概率的方程来描述。概率的估计可以从探测器物理的简单模型中得出。
