Sensitivity improvement of time-of-flight (ToF)-PET detector through recovery of Compton scattered annihilation photons

In PET detector designs, the scintillator material can be partitioned such that a block of crystals share timing/energy readout electronics. A fraction of the incident 511 keY photons produce simultaneous events in two adjacent block readouts due to Compton scattering followed by escape from the primary block. These inter-block Compton scatter events are typically not processed in current PET scanners. We have used radiation transport simulations to determine the fraction of inter-block Compton events for different block sizes using LYSO scintillator. The simulations showed the statistical distribution of the energy signals and time stamps in the two blocks and guided the selection of energy and time criteria for an event recovery algorithm. With a particular block size, we experimentally demonstrated that inter-block Compton events may be recovered as valid events with a corrected time stamp and estimated position of initial interaction. The results showed a significant improvement in detector sensitivity at the expense of a small degradation in the timing resolution of the detector block.