OSEM重建算法中几个关键问题的研究

目的：改进平行孔准直器SPECT系统的成像方法，快速、精确地实现有序子集期望值最大化（OSEM）重建算法。方法：采用理想平行孔和张角效应平行孔准直器两种模型，将准直器的空间响应融入系统传输矩阵，利用改进的射线跟踪算法进行衰减校正。结果：随着准直器张角的增加，Jaszczak模型的重建图像在边界出现明显的亮环；利用考虑准直器空间响应的系统矩阵进行图像重建．能较好的抑制边界伪影。结论：融入准直器空间响应函数的系统矩阵更为精确、贴近真实情况，能较好的抑制边界伪影，提高了重建图像的对比度和信噪比。

Research on Some Key Problems in the OSEM Algorithm

Objective： To improve a reconstruction method of the parallel-hole SPECT system, fast and accurately realize the OSEM algorithm. Methods： By using a perfect parallel-hole collimator model and a collimator model considering the splayed angle effect, this paper proposed a novel method which considers the space response function （SRF） calculating the system matrix and uses an improved Ray Tracing algorithm to perform attenuation correction. Results： The Jaszczak phantom＇s edge overshoot artifact will appear and will more evidence with the increasing of angle the collimator splayed, but using the system matrix calculated from the novel method the edge artifact can be eliminated. Conclusion： After considering the SRF, the system matrix is more accurate, and the reconstruction image＇s contrast and SNR are improved.