针孔单光子发射计算机断层成像的空间分辨率研究

针孔单光子发射计算机断层(SPECT)成像的空间分辨率通常是根据Anger经验公式来进行估算,与实际测量存在较大偏差.本文通过对针孔成像的物理过程进行分析,提出了一个近似度更高的计算公式.利用精确的蒙特卡罗方法模拟针孔SPECT成像,采用OSEM(ordered subsets expectation maximization)算法对投影数据进行图像重建,并与模具实验进行比较,验证了理论公式的适用性.同时还讨论了体素尺寸、几何映射获取投影矩阵以及探测器尺寸与成像物体尺寸比值对断层图像空间分辨率的影响.实验结果显示,该理论公式所估算的空间分辨率比实验值平均偏小约10%,而Anger经验公式所估算的空间分辨率比实验值平均偏大约60%.因此,该理论公式能更好地估算针孔SPECT成像的空间分辨率,可为针孔SPECT系统的设计和使用提供有价值的参考.

Spatial resolution of pinhole single photon emission computed tomography imaging

The spatial resolution of pinhole single photon emission computed tomography (SPECT) imaging is usually estimated according to Anger' s empirical formula, which could result in a large inaccuracy in experimental measurement. We present a more accurate formula based on the analysis of physical processes of pinhole imaging. The effectiveness of the proposed formula was evaluated by accurate Monte Carlo simulations and experiments of the phantom imaging. The images were reconstructed using three-dimensional iterative OSEM algorithm. Then the effects of the voxel size, the geometrical mapping of the projection matrix and the ratio of detector size to imaging object size, on the spatial resolution were discussed. The experiment results show that the spatial resolution estimated by the proposed formula is about 10% smaller than the experimental value while the estimation by the Anger' s formula is about 60% larger than the experimental value. Therefore, our proposed formula is more accurate than Anger' s formula for predicting the spatial resolution of pinhole SPECT imaging, and it can be utilized for design and use of pinhole SPECT system.