Recent Developments in Detectors for High Spatial Resolution Positron CT

Experiments using three types of detectors for high spatial resolution positron CT have been carried out as follows : 1. One to one coupling between a BGO scintillator and a thin rectangular photomultiplier tube (PMT). 2. Combining a small position sensing PMT with two BGO scintillators. 3. Combining a large PMT with two or more BGO scintillators and using other detectors for scintillator identification -- a) small PMT's, b) silicon photodiodes (SiPD). The time resolution obtained in method 1 was poorer than that of the other methods due to the present status of thin PMT performance - poor cathode sensitivity. In method 2 and 3-a), good time resolution and position sensing were obtained. In method 3-b), the peak to valley ratio of 1.8 in pulse height spectrum was obtained with a cooled BGO scintillator and a SiPD.