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Fisher Information Analysis of Depth-of-Interaction Estimation in Double-sided Strip Detectors

机译：双面条带探测器中相互作用估计的Fisher信息分析

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Electron and holes, produced by the absorption of a gamma-ray photon in the depletion region of a semiconductor detector, drift towards their respective electrodes under the influence of the electric field created by a bias potential difference applied between the contacts. Carrier transport has an important impact on the signals observed with compound semiconductors such as CdTe and CdZnTe, as these materials are known to suffer from non-negligible trapping effects. Trapping causes the carrier-induced charge on the anodes and cathodes to become a function of where the electrons and holes are generated via the gamma-ray interaction in the crystal. The mean drift length of the charge carriers, and thus the significance of the effects of trapping, can be at least partially controlled by changing the magnitude of the applied bias voltage. Selection of operating bias voltage can therefore provide us a means to tune the sensitivity to gamma-ray depth-of-interaction (DOI). In very-high-resolution gamma-ray imaging applications, such as preclinical PET and SPECT, estimation of a 3D interaction location inside the detector crystal can be used to minimize parallax error in the imaging system. In this work, we investigate the effect of bias voltage setting on DOI estimates for a semiconductor detector with a double-sided strip geometry. We first examine the statistical properties of the signals and develop expressions for likelihoods for given gamma-ray interaction positions. Trapping effects are modeled as non-stationary spatial point processes. We use Fisher Information to quantify how well (in terms of variance) the measured signals can be used for DOI estimation with different bias-voltage settings. We performed measurements of detector response versus 3D position as a function of applied bias voltage by scanning with highly collimated synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory. Experimental and theoretical results show that the optimum bias setting depends on whether or not the estimated event position will include the depth of interaction. We also found that for this detector geometry, the Fisher Information changes with depth.
机译：通过在半导体检测器的耗尽区域中吸收伽马射线光子产生的电子和孔，在通过在触点之间施加的偏置电位差产生的电场的影响下朝向它们各自的电极。载体转运对用化合物半导体如CdTe和Cdznte观察到的信号产生重要影响，因为已知这些材料遭受不可忽略的诱捕效果。捕获使载体引起的阳极和阴极上的电荷变为电子和孔通过晶体中的伽马射线相互作用产生电子和孔的函数。电荷载波的平均漂移长度，因此通过改变所施加的偏置电压的大小来至少部分地控制捕获的效果的意义。因此，操作偏置电压的选择可以为我们提供一种调整伽马射线深度相互作用（DOI）的灵敏度的手段。在非常高分辨率的伽马射线成像应用中，例如临床前PET和SPECT，可以使用探测器晶体内的3D交互位置的估计来最小化成像系统中的视差误差。在这项工作中，我们研究了双面条带几何的半导体检测器DOI估计对DOI估计的影响。我们首先检查信号的统计特性，以及对给定伽马射线相互作用位置的似然表达表达。捕获效果被建模为非静止空间点过程。我们使用Fisher信息量化（在方差方面）测量信号可用于使用不同偏压设置的DOI估计。我们通过在Argonne National实验室的高级光子源上用高度准直的同步辐射扫描来执行检测器响应与3D位置的测量。实验和理论结果表明，最佳偏置设置取决于估计的事件位置是否包括相互作用的深度。我们还发现，对于该探测器几何形状，Fisher信息随深度而变化。

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