Performances of two flat panel multi-anode PMTs for readout from pixelated LGSO crystals

Objectives Hamamatsu H9500 and H8500 are the flat panel multi-anode PMTs which have been used for developing high resolution PET detectors. The 256 channel H9500 has the finer detector pixels than the 64 channel H8500. In this study, we assess the performances of these PMTs coupled with pixilated scintillation crystal array using Monte Carlo simulation and real experiments.

Methods We performed optical simulations by tracking individual photons. 5x5 and 7x7 arrays of LGOS crystals with the size of 2x2x10 mm³ and 1.5x1.5x10 mm³ respectively were attached to the center and corner of PMTs. Flood images were obtained by the weighted mean of center positions of the pixels where the photons reached. In the real experiments, we obtained the flood image using a ²²Na point source and charge-division positioning circuits.

Results Mean FWHMs for the peaks of flood images were 0.35 mm for H8500 and 0.34 mm for H9500. Energy resolutions were 12.5% for H8500 and 11.2% for H9500. At the center of both PMTs, all peaks were clearly separated for both 2x2x10 mm³ and 1.5x1.5x10 mm³ crystals. At the corner of PMTs, the last two lines of peaks were very close but visually separable in the H8500 flood images while the better crystal identification was possible with H9500. The simulation results were in good agreement with the experimental results.

Conclusions There were almost no differences in the performances between H8500 and H9500 PMTs except for the corner of the flood images. The H8500 PMT also might be usable to develop high resolution PET detectors with 2x2x10 mm³ and 1.5x1.5x10 mm³ crystals if the peaks at the corner of PMT are carefully separated.