A continuous crystal detector for TOF PET

Presently, a majority of Positron Emission Tomography (PET) systems is based on block-detectors consisting of many scintillating pixels read by photomultipliers (PMTs). An improvement of time resolution, due to a common light readout by a cluster of PMTs, proposed by Kuhn et al, and tested by us for an LSO crystal triggered an idea of the new PET detector optimized for the Time of Flight (TOF) systems, based on a continuous crystal. In the present work, optimization of timing for a 20×20×20 mm³ LYSO crystal coupled to the 16-channel photomultiplier H8711-200MOD from Hamamatsu is presented. First, the measurements of transit time jitter, number of photoelectrons and time resolution with a small 10×10×5 mm³ LSO crystal coupled to the H8711-200MOD PMT were performed. Results were compared with data collected for fast timing photomultipliers like Photonis XP1020, XP3060, XP20D0 or Hamamatsu R9800. In the second part of the study, the time resolution measurements and the optimization of the system with the continuous LYSO crystal were made. Also simple tests with positioning of gamma interaction inside the scintillator are reported. The final results are discussed in terms of the measured photoelectron number and requirements for the TOF-PET scanners.