基于蒙特卡罗模拟的小动物质子CT最优射束能量

目的 观察基于蒙特卡罗模拟的小动物质子CT （PCT）的最优射束能量。方法 采用蒙特卡罗模拟建立PCT系统，分别以不同能量质子束对体模1、2进行扫描，并以滤波反投影法重建图像，观察其中不同材料质子的相对阻止本领（RSP）值、重建误差、空间分辨率、信号噪声比（SNR）及对比噪声比（CNR），评估图像质量，筛选最优质子射束能量。结果 重建图像中，特氟龙、聚丙烯及骨骼等效材料的RSP的相对误差均随质子能量增高而先降后升，于质子能量为130 MeV时最小，分别为0.76%、0.08%及0.05%。体模1内4种插件的SNR和CNR均随质子能量增高而降低。重建图基本无法分辨体模2内直径0.2 mm铝插件，质子能量较低时可分辨直径0.4 mm铝插件；不同质子能量下均可分辨直径0.8 mm铝插件，且空间分辨率随质子能量增高而提升，质子能量大于130 MeV后变化趋缓。结论 以蒙特卡罗模拟的小动物PCT平台的最优成像质子射束能量为130 MeV。

Optimal beam energy of proton CT for small animals based on Monte Carlo simulation

Objective To screen the optimal beam energy of proton CT (PCT) for small animals based on Monte Carlo simulation. Methods A PCT system was established based on Monte Carlo simulation, which was used to scan phantom 1 and phantom 2 with proton beam of different energies, and the original PCT images were reconstructed with filtered back projection method. Proton relative stopping power (RSP) value, reconstruction error, spatial resolution, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of different materials in reconstructed images were observed to evaluate the image quality, and the optimal beam energy of proton was analyzed. Results On the reconstructed images, the relative errors of reconstructed RSP of Teflon, polypropylene and Bone-100 all first decreased and then increased with the increase of proton energies, and the relative errors were the smallest when the proton energy was 130 MeV, i.e. 0.76%, 0.08% and 0.05%, respectively. SNR and CNR of 4 kinds of inserts in phantom 1 decreased with the increase of proton energies. On the reconstructed images of phantom 2, it was difficult to distinguish the aluminum insert with diameter of 0.2 mm, those with a diameter of 0.4 mm could be distinguished with low proton energies, while those with diameter of 0.8 mm could be distinguished under different proton energies. The spatial resolution increased with the increase of proton energies, and the change trend gradually slowed down with proton energies greater than 130 MeV. Conclusion The optimal beam energy of proton PCT for small animals based on Monte Carlo simulation for imaging was 130 MeV.