Test and optimization of timing algorithms for PET detectors with digital sampling front-end

We tested a digital front-end concept in order to evaluate the time resolution of PET detectors based on APD or PMT with digital read-out. Measurements were done on a coincidence set-up with two detection blocks composed of a fast inorganic scintillator (LaBr 3 or LYSO) coupled to a photodetector (APD or PMT), preamplificators and prefilters. The signals were sampled at high rate (250MHz for APDs, 5GHz for PMTs) and treated offline. Two different timing algorithms were applied: a digital method deriving from constant fraction discriminator, and an optimal filtering technique based on parameter estimation with minimal variance. The classical optimal filter was adapted to the non-stationary noise conditions, with a significant improvement of timing resolution. We describe these algorithms and discuss their performances.