Development of a Position-Sensitive Detector for TOF-PET

A position-sensitive detector (PS-detector) for a time-of-flight (TOF) PET system has been developed and evaluated. The PS-detector consists of a flat panel position-sensitive photomultiplier tube (PS-PMT; Hamamatsu R8400-00-M64 MOD) and 2.9 mm times 2.9 mm times 20 mm LYSO crystals arranged in a 16 times 16 array. The PS-PMT has eight stages of metal channel dynode and 8 times 8 multiple anodes in a 52.0 mm square times 14.8 mm high metal can package. In order to compensate for the non-uniform amplitude from the multiple anodes of the PS-PMT, an application specific integrated circuit (ASIC) having 64-channel variable gain amplifiers is attached to the front-end circuits. The ASIC also has a readout circuit to reduce 64-channel outputs down to four position signals and an energy signal. The performance of PS-detector was evaluated for TOF-PET application. The coincidence response functions (CRFs) were measured by scanning a ²²Na point source with 0.4 mm steps across the center of a pair of the PS-detectors. The average FWHM value of the CRFs is 2.3 mm. The energy resolution corresponding to each crystal element at 511 keV is 10.9% on the average. The timing resolutions of the PS-detector at FWHM, with a BaF₂ reference detector, range from 421 ps to 787 ps, with an average of 505 ps. A new PS-PMT having high QE is now under development. The timing resolutions of the new PS-PMT coupled to a LaBr₃ and a LYSO single crystal are 236 ps FWHM and 366 ps FWHM, respectively, with a BaF₂ reference detector. We are developing a new TOF-PET system with PS-detectors.