Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China.
Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen, 518055, China.
Med Phys. 2022 Mar;49(3):1432-1444. doi: 10.1002/mp.15455. Epub 2022 Jan 27.
The performance of small animal PET scanners depends on the energy window (EW) and timing window (TW). In National Electrical Manufacturers Association (NEMA) Standards Publication NU 4-2008, detailed procedures of the performance measurements are defined, but the EW and TW are not specified. In this work, the effects of EW and TW on the physical and imaging performance of Shenzhen Institute of Advanced Technology small animal PET (SIAT aPET) will be evaluated.
First, the flood histogram, energy resolution, and timing resolution were measured for a detector of SIAT aPET. Second, the spatial resolutions were measured with different EWs. Third, the sensitivities, the scatter fractions (SFs), and noise equivalent count rates (NECRs) of a mouse-sized phantom and a rat-sized phantom, the recovery coefficients (RCs) of rods of different sizes, and the percentage standard deviation (%STD) of the NEMA image quality phantom were measured for different EWs and TWs. Last, images of a hot rod phantom, a mouse heart, and a rat brain were acquired from the scanner with different EWs.
The SIAT aPET detectors provided good flood histograms such that all but the corner crystals can be resolved even with lower energies of 250-350 keV, an average energy resolution of 21.1 ± 1.9%, and an average timing resolution of 2.63 ± 0.69 ns. The average spatial resolutions obtained with EWs of 250-350 keV and 450-550 keV are 0.68 mm and 0.75 mm. For EWs of 250-750 keV, 350-750 keV, and 450-750 keV with a fixed TW of 12 ns, the sensitivities at the center of field of view (FOV) are 16.0%, 11.9%, and 8.2%, the peak NECRs of a mouse-sized phantom are 355.6 kcps, 324.4 kcps, and 249.4 kcps, and the peak NECRs of a rat-sized phantom are 148.5 kcps, 144.3 kcps, and 117.7 kcps, respectively. For the TWs of 4 ns, 8 ns,12 ns, and 20 ns with a fixed EW of 350-750 keV, the sensitivities at the center of FOV are 9.6%, 11.4%, 11.9%, and 12.2%, the peak NECRs of a mouse-sized phantom are 260.1 kcps, 311.5 kcps, 324.4 kcps and 324.9 kcps, and the peak NECRs of a rat-sized phantom are 110.5 kcps, 137.3 kcps, 144.3 kcps, and 142.6 kcps, respectively. Narrowing the EW and TW improves the RCs of rods of all sizes, and the %STD of images obtained with different EWs and TWs are similar. Rods with diameter down to 0.8 mm can be visually resolved from images of the hot rod phantom obtained with different EWs. Images of mouse heart with high spatial resolution and rat brain with detail brain structure were obtained with different EWs. Images of both phantom and in vivo animals obtained with different EWs only showed subtle difference.
The performance of SIAT aPET under different EWs and TWs was compared. The EW and TW affect the sensitivity, SF, and NECR but not the spatial resolution and animal images of SIAT aPET, which imply that careful optimization of the EW and TW is not required.
小动物 PET 扫描仪的性能取决于能量窗 (EW) 和定时窗 (TW)。在国家电器制造商协会 (NEMA) 标准出版物 NU 4-2008 中，定义了性能测量的详细程序，但未指定 EW 和 TW。在这项工作中，将评估深圳先进技术研究院小动物 PET (SIAT aPET) 的 EW 和 TW 对其物理和成像性能的影响。
首先，测量 SIAT aPET 探测器的洪水直方图、能量分辨率和定时分辨率。其次，使用不同的 EW 测量空间分辨率。第三，使用不同的 EW 和 TW 测量小鼠大小的体模和大鼠大小的体模的灵敏度、散射分数 (SF) 和噪声等效计数率 (NECR)、不同大小的棒的恢复系数 (RC) 和 NEMA 图像质量体模的百分比标准偏差 (%STD)。最后，使用不同的 EW 采集热棒体模、小鼠心脏和大鼠大脑的图像。
SIAT aPET 探测器提供了良好的洪水直方图，即使使用 250-350keV 等较低的能量，也可以分辨出除了角落晶体之外的所有晶体，平均能量分辨率为 21.1 ± 1.9%，平均定时分辨率为 2.63 ± 0.69ns。使用 250-350keV 和 450-550keV 的 EW 获得的平均空间分辨率分别为 0.68mm 和 0.75mm。对于 250-750keV、350-750keV 和 450-750keV 的 EW 和固定的 12ns TW，视野 (FOV) 中心的灵敏度分别为 16.0%、11.9%和 8.2%，小鼠大小体模的峰值 NECR 分别为 355.6 kcps、324.4 kcps 和 249.4 kcps，大鼠大小体模的峰值 NECR 分别为 148.5 kcps、144.3 kcps 和 117.7 kcps。对于固定 EW 为 350-750keV 的 4ns、8ns、12ns 和 20ns 的 TW，FOV 中心的灵敏度分别为 9.6%、11.4%、11.9%和 12.2%，小鼠大小体模的峰值 NECR 分别为 260.1 kcps、311.5 kcps、324.4 kcps 和 324.9 kcps，大鼠大小体模的峰值 NECR 分别为 110.5 kcps、137.3 kcps、144.3 kcps 和 142.6 kcps。缩小 EW 和 TW 可提高所有尺寸棒的 RC，并且使用不同 EW 和 TW 获得的图像的 %STD 相似。从使用不同 EW 获得的热棒体模图像中可以看到直径降至 0.8mm 的棒。使用不同的 EW 获得了具有高空间分辨率的小鼠心脏和具有详细脑结构的大鼠大脑的图像。使用不同 EW 获得的体模和体内动物的图像仅显示出细微的差异。
比较了 SIAT aPET 在不同 EW 和 TW 下的性能。EW 和 TW 影响灵敏度、SF 和 NECR，但不影响 SIAT aPET 的空间分辨率和动物图像，这意味着不需要仔细优化 EW 和 TW。
