Time of flight coincidence timing calibration techniques using radioactive sources

The coincidence timing offset must be measured accurately and robustly in order to elicit the best performance for a time of flight (TOF) PET scanner. The proposed calibration methods involve measuring the timing differences between multiple coincidence line pairs. The absolute time biases for each pixel on the detector are assumed to be independent which greatly reduces the number of counts that are needed for a good estimate. It is not a requirement that each pixel on the detector be measured in coincidence with every other pixel on the detector, but that the coincidences involve a reasonably large number of different pixels on the opposite side. The intrinsic timing offset for each detector crystal pixel is unfolded by forming the average of the offset values of each crystal pixel with opposing pixels to average out crystal variations and photomultiplier (PMT) timing differences. In this work, a comparison is made of different timing calibration techniques using radioactive sources, specifically a rotating line source and a point source in a scattering block. The calibrations using the different methods are performed on a prototype TOF scanner and the results are presented