Evaluation of Position Sensitive Photomultiplier for Time-of-Flight Positron Emission Tomography

We have evaluated a position sensitive photomultiplier from Hamamatsu, H8500, for time-of-flight detector application and would propose it as a great possibility. A LYSO multi-crystal array of 12 times 12 was designed for H8500. The front surface dimension of the crystal block was 51 times 51 mm² and its individual crystal dimension was 4.2 times 4.2 times 30 mm³. Two different block schemes, air-gap and isolation, were made for the comparison. Blocks were optically coupled to H8500. Since H8500 had a 1.5 mm dead area on each edge, edge crystals were not fully covered by the active photocathode. A resistive network was used in the preamplifier to reduce 64 anode outputs down to four. Four summed anode outputs were processed for light output and energy resolution measurement. For timing measurement, the output of the last dynode 12 was utilized against a fast plastic detector. Edge crystals showed poor results as expected, but the average energy and timing resolutions were 11% and 485 ps (crystal to crystal), respectively, among the middle crystals in the block. The variation of transit time difference was 130 ps implying its good timing capability for wide area. So, we concluded that position sensitive photomultiplier, H8500, could be a good candidate for the time-of-flight PET detector.