Development of Ultra-high Resolution Single Photon Emission Computed Tomography(SPECT) Using Pinhole-Collimator

小动物放射性核素成像对放射性药物的开发和各种动物疾病模型的研究具有重要意义。虽然今天的SPECT系统提供了很好的分辨率（8-10mm），但这些还不足以用于小动物研究，包括大鼠，小鼠和沙鼠。为了实现小于2mm的空间分辨率，我们尝试使用针孔准直器构建超高分辨率SPECT系统。针孔准直器由锥形铅屏蔽和有效孔径分别为1.0和2.0mm的钨针孔组成。四个针孔准直器连接到4头SPECT扫描仪与固定距离从针孔到相机（130mm）和从针孔到旋转轴（50mm）。视野直径50mm，轴向12.3mm，最小切片厚度0.51mm。在扇形并行投影数据转换后，采用滤波反投影算法重建SPECT图像。系统空间分辨率为1.65mm (FWHM)，灵敏度为116 cps/kBq/ml，配备1.0mm针孔准直器。用Tc-99m血流示踪剂对大鼠进行动物实验，脑结构和心肌壁清晰可见。大鼠脑苯二氮卓类药物受体动态SPECT成像显示各脑区意义时间活动曲线。这种超高分辨率针孔SPECT系统将有助于开发新的放射性药物和活体动物疾病模型。

Radionuclide imaging of small animals is useful for development of the radiopharmaceuticals as well as for studying various animal disease models. Although todays SPECT systems provide an excellent resolution(8-10mm), these are not sufficient for small animal studies including rats, mice and gerbils.In order to achieve less than 2mm spatial resolution, we have attempted to construct an ultra-high resolution SPECT system using pinhole collimators. The pinhole collimator were made of cone shaped lead shield and tungsten pinhole with effective aperture size of 1.0 and 2.0mm. Four pinhole collimators are attached to 4-head SPECT scanner with fixed distance from pinhole to camera (130mm) and from pinhole to rotating axis (50mm). The field of view was 50mm in diameter and 12.3mm in axial direction with minimum slice thickness of 0.51mm. Filtered back projection algorithm was used to reconstruct SPECT images after fan-parallel projection data conversion.The system provided spatial resolution of 1.65mm (FWHM) and sensitivity of 116 cps/kBq/ml with 1.0mm pinhole collimator. In animal studies by rats with Tc-99m blood flow tracers, brain structures and myocardial wall were resolved clearly. Dynamic SPECT imaging of benzodiazepine receptor in rat brain showed the meaning time activity curves at every region of the brain.This ultra-high resolution pinhole SPECT system will contribute to development of new radiopharmaceuticals and disease models in living animals.