Ogata Yuma, Ohnishi Takashi, Moriya Takahiro, Inadama Naoko, Nishikido Fumihiko, Yoshida Eiji, Murayama Hideo, Yamaya Taiga, Haneishi Hideaki
Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan.
Radiol Phys Technol. 2014 Jan;7(1):35-42. doi: 10.1007/s12194-013-0228-z. Epub 2013 Jul 30.
The X'tal cube is a next-generation DOI detector for PET that we are developing to offer higher resolution and higher sensitivity than is available with present detectors. It is constructed from a cubic monolithic scintillation crystal and silicon photomultipliers which are coupled on various positions of the six surfaces of the cube. A laser-processing technique is applied to produce 3D optical boundaries composed of micro-cracks inside the monolithic scintillator crystal. The current configuration is based on an empirical trial of a laser-processed boundary. There is room to improve the spatial resolution by optimizing the setting of the laser-processed boundary. In fact, the laser-processing technique has high freedom in setting the parameters of the boundary such as size, pitch, and angle. Computer simulation can effectively optimize such parameters. In this study, to design optical characteristics properly for the laser-processed crystal, we developed a Monte Carlo simulator which can model arbitrary arrangements of laser-processed optical boundaries (LPBs). The optical characteristics of the LPBs were measured by use of a setup with a laser and a photo-diode, and then modeled in the simulator. The accuracy of the simulator was confirmed by comparison of position histograms obtained from the simulation and from experiments with a prototype detector composed of a cubic LYSO monolithic crystal with 6 × 6 × 6 segments and multi-pixel photon counters. Furthermore, the simulator was accelerated by parallel computing with general-purpose computing on a graphics processing unit. The calculation speed was about 400 times faster than that with a CPU.
X'tal 立方体是我们正在研发的一款用于正电子发射断层扫描（PET）的下一代深度交互探测器，旨在提供比现有探测器更高的分辨率和更高的灵敏度。它由一块立方体型的整体闪烁晶体和硅光电倍增管构成，硅光电倍增管耦合在立方体六个表面的不同位置。采用激光加工技术在整体闪烁晶体内部制造由微裂纹组成的三维光学边界。当前配置基于对激光加工边界的经验性试验。通过优化激光加工边界的设置，仍有提高空间分辨率的空间。事实上，激光加工技术在设置边界参数（如尺寸、间距和角度）方面具有高度的自由度。计算机模拟可以有效地优化这些参数。在本研究中，为了正确设计激光加工晶体的光学特性，我们开发了一种蒙特卡罗模拟器，它可以对激光加工光学边界（LPB）的任意排列进行建模。通过使用带有激光器和光电二极管的装置测量 LPB 的光学特性，然后在模拟器中进行建模。通过比较模拟得到的位置直方图与使用由 6×6×6 个单元的立方体型 LYSO 整体晶体和多像素光子计数器组成的原型探测器进行实验得到的位置直方图，证实了模拟器的准确性。此外，通过在图形处理单元上进行通用计算的并行计算加速了模拟器。计算速度比使用中央处理器（CPU）快约 400 倍。
