Development of a software for nonounifrom attenuation and scatter correction in SPECT using XCT data

1. 基于x射线CT图像数据的SPECT非均匀衰减校正算法设计(1)算法的构建。基于Chang、Tanaka和Singh的三种方法，构建了三种算法。前两种方法最初是为了均匀衰减校正而提出的，但在算法中对它们进行了修改，用于非均匀衰减校正。从计算机实验中发现，它们的一阶修正不能产生很好的修正结果，而二阶修正只需一次迭代就能得到令人满意的结果。(2)临床应用中的问题。发现了两个主要问题：XCT图像与相应的SPECT未校正图像解剖位置的重合，以及XCT图像x射线平均能量的确定。该信息用于将XCT的衰减数据转换为SPECT的衰减数据。解决这些问题是在临床应用中实现准确衰减校正的关键。散射校正对探测到的光子散射辐射进行了初步的理论评估，但其在单个SPECT图像上的应用在计算时间上是不现实的。结果表明，利用多能窗探测到的光子计数计算散射辐射是一种具有实际应用前景的精确散射校正方法。正在对这个问题进行更详细的研究。

1. Design of algorithm for nonunifrom attenuation correction in SPECT using x-ray CT image data(1) Construction of the algorithm.Three kinds of the algorithm were constructed which are based on three methods reported by Chang, Tanaka, and Singh.The first two had originally been proposed for uniform attenuation correction, but in the algorithm they were modified for nonunifrom attenuation correction.From computer experiments, it was found that their first-order correction did not produce good correction results, but their second-order correction gave satisfactory resulsts only with a single iteration.(2) Problems in clinical applications.Two major problems were found : the coincidence of anatomical positions between XCT image and the corresponding uncorrected image for SPECT,and the determination of average X-ray energy for the XCT image.This information is used when converting attenuation data for XCT to those attenuation for SPECT.A solution for the problems is the key to accurate attenuation correction in clinical applications.2. Scatter correctionA theoretical evaluation of scattered radiation in detected photons was planned primarily, but its application to individual SPECT images was not practical in computation time.It was concluded that a practically promising method for accurate scatter correction is to evaluate scattered radiation from photon counts detected with plural energy windows.More detailed studies of this subject are being carried out.