Hirano Yoshiyuki, Koshino Kazuhiro, Iida Hidehiro
Department of Bio-medical Imaging, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita City, Osaka, 565-8565 Japan. Present address: Gunma University Heavy Ion Medical Center, 3-39-22, Showa-Machi, Maebashi, Gunma 371-8511, Japan.
Phys Med Biol. 2017 May 21;62(10):4017-4030. doi: 10.1088/1361-6560/aa6644. Epub 2017 Mar 13.
Monte Carlo simulation is widely applied to evaluate the performance of three-dimensional positron emission tomography (3D-PET). For accurate scatter simulations, all components that generate scatter need to be taken into account. The aim of this work was to identify the components that influence scatter. The simulated geometries of a PET scanner were: a precisely reproduced configuration including all of the components; a configuration with the bed, the tunnel and shields; a configuration with the bed and shields; and the simplest geometry with only the bed. We measured and simulated the scatter fraction using two different set-ups: (1) as prescribed by NEMA-NU 2007 and (2) a similar set-up but with a shorter line source, so that all activity was contained only inside the field-of-view (FOV), in order to reduce influences of components outside the FOV. The scatter fractions for the two experimental set-ups were, respectively, 45% and 38%. Regarding the geometrical configurations, the former two configurations gave simulation results in good agreement with the experimental results, but simulation results of the simplest geometry were significantly different at the edge of the FOV. From the simulation of the precise configuration, the object (scatter phantom) was the source of more than 90% of the scatter. This was also confirmed by visualization of photon trajectories. Then, the bed and the tunnel were mainly the sources of the rest of the scatter. From the simulation results, we concluded that the precise construction was not needed; the shields, the tunnel, the bed and the object were sufficient for accurate scatter simulations.
蒙特卡罗模拟被广泛应用于评估三维正电子发射断层扫描（3D-PET）的性能。为了进行准确的散射模拟，需要考虑所有产生散射的组件。这项工作的目的是确定影响散射的组件。PET扫描仪的模拟几何结构包括：精确复制所有组件的配置；带有检查床、通道和屏蔽的配置；带有检查床和屏蔽的配置；以及仅带有检查床的最简单几何结构。我们使用两种不同的设置测量和模拟了散射分数：（1）按照NEMA-NU 2007的规定；（2）一种类似的设置，但使用较短的线源，以便所有放射性活度仅包含在视野（FOV）内，以减少视野外组件的影响。两种实验设置的散射分数分别为45%和38%。关于几何配置，前两种配置的模拟结果与实验结果吻合良好，但最简单几何结构的模拟结果在视野边缘有显著差异。从精确配置的模拟中，物体（散射体模）是超过90%散射的来源。这也通过光子轨迹的可视化得到了证实。然后，检查床和通道主要是其余散射的来源。从模拟结果中，我们得出结论，不需要精确的结构；屏蔽、通道、检查床和物体足以进行准确的散射模拟。
