An analytical model of the effects of pulse pileup on the energy spectrum recorded by energy resolved photon counting x-ray detectors
An analytical model of the effects of pulse pileup on the energy spectrum recorded by energy resolved photon counting x-ray detectors
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DOI：
10.1118/1.3429056
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发表时间：
2010-08-01
期刊：
影响因子：
3.8
通讯作者：
Barber, William C.
中科院分区：
文献类型：
--
作者：
Taguchi, Katsuyuki;Frey, Eric C.;Barber, William C.
目的：近年来，具有能量分辨能力的新型CdTe光子计数X射线探测器(PCXD)被开发出来。然而，当这种探测器在高X射线通量下工作时，重合脉冲会扭曲记录的能谱。这些失真称为脉冲堆积效应。为了充分利用PCXD提供的光谱信息，必须补偿这些对记录能谱的影响。这种补偿可以通过将堆积模型合并到用于计算机断层扫描的图像重建过程中，即作为前向成像过程的一部分，并且使用例如最大似然方法迭代地估计成像对象或线积分来实现。针对非瘫痪探测器的峰和尾堆积效应，提出了一种新的脉冲堆积解析模型。方法：该模型考虑了脉冲的双极形状、随机事件间时间间隔的分布函数和光子能量的输入概率密度函数等因素。结果：对于不同程度的脉冲堆积效应，由该模型估计的记录光谱与蒙特卡罗模拟得到的结果吻合较好。对于多色入射X射线谱，死区损失为1%~50%时的变异系数(即均方根差除以测量平均值)为5.3%~10.0%。结论：所提出的脉冲堆积模型可以较好地预测记录的谱。(C)2010年美国医学物理学家协会。[DOI：10.1118/1.3429056]
Purpose: Recently, novel CdTe photon counting x-ray detectors (PCXDs) with energy discrimination capabilities have been developed. When such detectors are operated under a high x-ray flux, however, coincident pulses distort the recorded energy spectrum. These distortions are called pulse pileup effects. It is essential to compensate for these effects on the recorded energy spectrum in order to take full advantage of spectral information PCXDs provide. Such compensation can be achieved by incorporating a pileup model into the image reconstruction process for computed tomography, that is, as a part of the forward imaging process, and iteratively estimating either the imaged object or the line integrals using, e.g., a maximum likelihood approach. The aim of this study was to develop a new analytical pulse pileup model for both peak and tail pileup effects for nonparalyzable detectors.Methods: The model takes into account the following factors: The bipolar shape of the pulse, the distribution function of time intervals between random events, and the input probability density function of photon energies. The authors used Monte Carlo simulations to evaluate the model.Results: The recorded spectra estimated by the model were in an excellent agreement with those obtained by Monte Carlo simulations for various levels of pulse pileup effects. The coefficients of variation (i.e., the root mean square difference divided by the mean of measurements) were 5.3%-10.0% for deadtime losses of 1%-50% with a polychromatic incident x-ray spectrum.Conclusions: The proposed pulse pileup model can predict recorded spectrum with relatively good accuracy. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3429056]