Non-uniform gamma ray event distribution in regionalized PET detector

A TOF PET detector based on SiPM was developed for a PET-MR scanner. The detector optimization to achieve the best timing resolution, by balancing between the active area of SiPMs and the crystal block size, led to a regionalized flood map with three distinctive areas. With the flood map, we discovered that 511keV singles event distribution was non-uniform. The cause was found out to be due to Compton scatter events in the regionalized map. A Monte-Carlo simulation confirmed the observation and we also demonstrated that the uniform flood map yielded a uniform 511keV singles event distribution in the data. With the result, we concluded that the same applies to any regionalized or non-uniform flood map that can be manifested with DOI, PSAPD or SiPM detectors. They would show a non-uniform singles distribution when scintillation light is regionally isolated or any crystal region in a flood map is not equally distributed.