用于能量分辨光子计数 X 射线探测器记录的能谱的脉冲堆积影响的分析模型。
An analytical model of the effects of pulse pileup on the energy spectrum recorded by energy resolved photon counting x-ray detectors.
机构信息
Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
出版信息
Med Phys. 2010 Aug;37(8):3957-69. 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.
目的
最近，具有能量分辨能力的新型碲化镉光子计数 X 射线探测器（PCXD）已经开发出来。然而，当这些探测器在高 X 射线通量下运行时，符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，必须对记录的能谱进行这些效应的补偿。这种补偿可以通过将堆积模型纳入计算机断层扫描的图像重建过程来实现，也就是说，作为正向成像过程的一部分，并且使用最大似然方法等迭代地估计成像物体或线积分。本研究的目的是为非瘫痪探测器的峰堆积效应和尾部堆积效应开发一种新的分析脉冲堆积模型。
方法
该模型考虑了以下因素：脉冲的双极性形状、随机事件时间间隔的分布函数以及光子能量的输入概率密度函数。作者使用蒙特卡罗模拟来评估该模型。
结果
该模型估计的记录谱与各种程度的脉冲堆积效应的蒙特卡罗模拟结果非常吻合。对于具有多色入射 X 射线光谱的死时间损失为 1%-50%，变化系数（即均方根差除以测量值的平均值）为 5.3%-10.0%。
结论
所提出的脉冲堆积模型可以以相对较高的精度预测记录谱。
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