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

小动物的放射性核素显像对于放射性药物的开发以及各种动物疾病模型的研究是有用的。虽然目前的SPECT系统提供了很好的分辨率（8- 10 mm），但这些分辨率对于包括大鼠、小鼠和沙鼠在内的小动物研究是不够的，为了实现小于2 mm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和钨针孔组成，有效孔径分别为1.0和2.0mm。四个针孔准直器连接到四头SPECT扫描仪，针孔到相机的固定距离（130 mm）和针孔到旋转轴的固定距离（50 mm）。最小层厚0.51mm，视野直径50 mm，轴向12.3mm。系统采用1.0mm针孔准直器，空间分辨率为1.65mm（FWHM），灵敏度为116 cps/kBq/ml。在动物实验中，大鼠用Tc-99 m血流示踪剂，脑结构和心肌壁清晰地解决。大鼠脑内苯二氮卓类受体的动态SPECT显像显示了脑内各区域有意义的时间活动曲线，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.