Peng Peng, Liu Chih-Chieh, Du Junwei, Bai Xiaowei, Cherry Simon R
Department of Biomedical Engineering, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
Biomed Phys Eng Express. 2018 Mar;4(2). doi: 10.1088/2057-1976/aaaa84. Epub 2018 Feb 9.
This work presents a method to improve the separation of edge crystals in PET block detectors. As an alternative to square-shaped crystal arrays, we used an array of triangular-shaped crystals. This increases the distance between the crystal centres at the detector edges potentially improving the separation of edge crystals. To test this design, we have compared the flood histograms of two 4×4 scintillator arrays in both square and triangular configurations. The quality of the flood histogram was quantified using the fraction of events positioned in the correct crystal based on a 2D Gaussian fit of the segmented flood histograms. In the first study, the two crystal arrays were coupled with the SiPM directly using optical grease, and the flood histogram quality for the edge and corner crystals in the triangular-shaped array were much better than that for those crystals in the square-shaped array. The average light collection efficiency for the triangular-shaped array was 5.9% higher than that for the square-shaped array. The average energy resolution for the triangular and square shape array were 11.6% and 13.2% respectively. In the second study, two light guides with thickness 1 mm and 2 mm were used between the crystal arrays and the SiPM. The thicker lightguide degraded the light collection efficiency and energy resolution due to the light loss introduced by the light guide. However, in the 2-mm thick lightguide case, the flood histogram quality for the edge and corner crystals in the square-shaped array were improved due to better separation of those crystals in the flood histogram. Comparing the performance of the two crystal arrays with three different light guides, the triangular-shaped crystal array with no lightguide gave the best performance.
这项工作提出了一种改进PET块状探测器中边缘晶体分离的方法。作为方形晶体阵列的替代方案，我们使用了三角形晶体阵列。这增加了探测器边缘处晶体中心之间的距离，有可能改善边缘晶体的分离。为了测试这种设计，我们比较了两种4×4闪烁体阵列在方形和三角形配置下的泛光直方图。基于分割后的泛光直方图的二维高斯拟合，使用位于正确晶体中的事件比例来量化泛光直方图的质量。在第一项研究中，两个晶体阵列直接使用光学油脂与硅光电倍增管（SiPM）耦合，三角形阵列中边缘和角落晶体的泛光直方图质量比方形阵列中的那些晶体要好得多。三角形阵列的平均光收集效率比方形阵列高5.9%。三角形和方形阵列的平均能量分辨率分别为11.6%和13.2%。在第二项研究中，在晶体阵列和SiPM之间使用了厚度为1毫米和2毫米的两个光导。由于光导引入的光损失，较厚的光导降低了光收集效率和能量分辨率。然而，在2毫米厚光导的情况下，方形阵列中边缘和角落晶体的泛光直方图质量由于在泛光直方图中这些晶体的更好分离而得到改善。比较具有三种不同光导的两个晶体阵列的性能，无轻导的三角形晶体阵列性能最佳。
