Evaluation of local PMT triggering electronics for a TOF-PET scanner

The development of high light output scintillation crystals with fast decay times has made clinical whole body TOF-PET scanners possible. Current clinical systems based on LYSO have timing resolutions near 600ps (FWHM), but considerably better resolution is possible with faster scintillators. We have previously reported results for a prototype TOF-PET scanner using LaBr3 (5% Ce) as the scintillation crystal. These preliminary results were obtained using a “local” triggering electronics scheme, in which the seven PMTs used for energy and positioning measurements are also used to produce a trigger. The local triggering design is intended to reduce the effects of pulse pileup and noise, reducing deterioration of the timing resolution at high count rates, and allowing us to take full advantage of the timing properties of LaBr3. In this work we present the details of the implementation of our design, and demonstrate the impact of the size of the trigger zone on the system timing resolution with increasing count rate. Optimization of the system has allowed us to achieve a 375ps (FWHM) system timing resolution of our prototype scanner.