Engineering Research Center of Molecular and Neuro Imaging, Ministry of Education, School of Life Science and Technology, Xidian University, Xi'an, Shaanxi 710071, People's Republic of China.
Phys Med Biol. 2021 Aug 24;66(17). doi: 10.1088/1361-6560/ac195b.
The construction of photon propagation has a close relationship with the quality of reconstructed images. The classical Monte Carlo (MC) based method can model the photon propagation precisely, but it is time-consuming. The analytical method can often quickly construct a model, but its precision is a problem. How to fully exploit the advantages of the MC simulation and analytical model is an open problem. Inspired by the characteristics of the depth of interaction (DOI) detectors, which can help confirm the deposited position of a photon with DOI-encoding technology, we virtually discretize each crystal into several subcrystals to obtain the statistical distribution by MC-based simulation. Then, the statistical distribution is combined with a spatially variant solid-angle model. This combination strategy provides a hybrid model to describe photon propagation with relatively high accuracy and low computational cost. Three discretization schemes are compared to optimize the constructed photon propagation model. Several experiments are carried out to evaluate the performance of the proposed hybrid method. The metrics of full width at half maximum (FWHM), contrast recovery (CR), and coefficient of variation (COV) are adopted to quantitate the imaging results. The classical MC-based method is compared as a gold-standard reference. When a crystal is divided into two discretized positions, the convergent tendencies of CRs and COVs are consistent with that based on MC simulation method, respectively. In terms of FWHMs, the resolutions of using the MC-based model and the proposed hybrid model are 0.71 mm and 0.68 mm in the direction parallel to the detector head, respectively. This indicates the potential of the proposed method in positron emission tomography imaging.
光子传播的构建与重建图像的质量密切相关。基于经典的蒙特卡罗（MC）方法可以精确地模拟光子的传播，但计算时间较长。分析方法通常可以快速构建模型，但精度是一个问题。如何充分利用 MC 模拟和分析模型的优势是一个悬而未决的问题。受深度-of-interaction（DOI）探测器的特性启发，该探测器可以利用 DOI 编码技术帮助确认光子的沉积位置，我们通过基于 MC 的模拟将每个晶体虚拟地离散化为几个子晶体，以获得统计分布。然后，将统计分布与空间变化的立体角模型相结合。这种组合策略提供了一种混合模型，可以以相对较高的精度和较低的计算成本来描述光子的传播。比较了三种离散化方案，以优化构建的光子传播模型。进行了多项实验来评估所提出的混合方法的性能。采用全宽半最大值（FWHM）、对比度恢复（CR）和变异系数（COV）等指标来定量成像结果。将基于经典 MC 的方法作为金标准参考进行比较。当将晶体分为两个离散位置时，CR 和 COV 的收敛趋势分别与基于 MC 模拟方法的收敛趋势一致。在 FWHMs 方面，基于 MC 模型和所提出的混合模型的分辨率分别在平行于探测器头部的方向上为 0.71mm 和 0.68mm，这表明了该方法在正电子发射断层成像中的潜力。
