Abstract：[Objective] Single photon emission computed tomography (SPECT) is an important imaging method of radionuclide bone imaging. It can obtain noninvasive three-dimensional functional images for early diagnosis and staged prognostic evaluation of disease by detecting γ photons emitted by radioactive drugs in the human body. According to the results of the national nuclear medicine census in 2020, more than 60% of SPECT clinical examinations in China are bone system examinations, indicating a great demand for bone imaging. Bone system examination generally refers to bone scanning, which is a nuclear medical imaging examination for systemic bones and can effectively diagnose various primary or secondary bone tumors. However, the low-energy general-purpose parallel-hole collimator, which is clinically used for SPECT bone scanning, has a low detection sensitivity, which leads to low patient comfort and scanning efficiency. Thus, this study aimes to optimize the detection sensitivity of SPECT system for bone imaging in clinical practice, which can not only reduce bone scanning time but also improve bone scanning efficiency and increase clinical-conomic benefits.[Methods] Based on the clinical dual-head SPECT system, this paper designed a specific collimator for bone imaging with high detection sensitivity. This study focuses on simulation experiments, including the construction of an overall simulation system, design of collimator parameters, and performance evaluation. The overall simulation system refers to the parameters of the SPECT system developed by this paper's cooperative company. In collimator parameter design, based on the formula derived in theory, which guides this paper in identifying the factors related to the detection sensitivity and resolution of SPECT system, different collimator parameters are tested by changing the collimator thickness, hole spacing, and hole diameter. Then, a Monte Carlo simulation, which is supported by center of high performance computing, Tsinghua University, is conducted with a point source for performance evaluation, including the detection sensitivity and image spatial resolution.[Results] The results indicates that the relationship between the geometric parameters and performance of the collimator matched well with the theoretical formula:as the increase of hole septal increases, the effective area of photon penetration on the collimator decreases, which reduces the detection sensitivity, while there is no obvious change in the image resolution. As the aperture increases, the collimation effect of the collimator is weakened, resulting in a serious decline in resolution. However, more scintillation photons will reach the scintillation crystal, there by hugely improving the detection sensitivity. When the aperture becomes larger, the improvement in detection sensitivity cannot make up for the loss brought by the reduction in resolution. When the collimator thickens, the collimation effect is enhanced, and the number of oblique incident photons that can be detected is reduced, so the detection sensitivity shows a downward trend. However, the image resolution can be improved.[Conclusions] Thinning the collimator and hole diameter is feasible in designing the SPECT collimator for bone scanning. According to the results of the performance evaluation, a collimator design (collimator thickness, 25.5 mm; hole septal, 0.15 mm; hole diameter, 0.5 mm) is empirically selected. It has a detection sensitivity of 183 cpm/μCi and a spatial resolution of 13.6 mm, which can significantly reduce the bone scanning acquisition time while ensuring image quality. The imaging effect of the collimator is evaluated using a hot-rod phantom experiment. The results show that hot rods with a 5.5-mm diameter could be distinguished, demonstrating the imaging performance of our proposed dedicated collimator design for bone scanning.
王喆鑫, 刘辉, 程李, 高丽蕾, 吕振雷, 江年铭, 何作祥, 刘亚强. 基于Monte Carlo模拟的全身骨扫描SPECT专用准直器设计[J]. 清华大学学报（自然科学版）, 2023, 63(5): 811-817.
WANG Zhexin, LIU Hui, CHENG Li, GAO Lilei, LV Zhenlei, JIANG Nianming, HE Zuoxiang, LIU Yaqiang. Design of dedicated collimator for whole-body bone scanning on single photon emission computed tomography based on Monte Carlo simulation. Journal of Tsinghua University(Science and Technology), 2023, 63(5): 811-817.
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2023, Vol. 63 
