Positioning Annihilation Photon Interactions in a Thin LSO Crystal Sheet With a Position-Sensitive Avalanche Photodiode

A.M.K Foudray,C.S Levin,F Habte,P.D Olcott

doi:10.1109/tns.2006.877178

Abstract

Using scintillation crystal sheets instead of discrete crystal arrays in high-resolution PET has the immediate advantage of reduced complexity as well as a potential for increased sensitivity. In order to evaluate the positioning capability of a position sensitive avalanche photodioide (PSAPD) using a sheet Lutetium Oxyorthosilicate (LSO) crystal scintillator, we studied the dependence of detected event position versus the known source position. In particular, we studied positioning in a continuous 8 mmtimes8 mm LSO sheet coupled to a PSAPD with an 8 mmtimes8 mm active area experimentally, studied optical transport in the sheet crystal with Monte Carlo simulation, and used two positioning methods to evaluate PSAPD pincushioning effects. Both collimated 57 Co 122 keV and coincidence-triggered 22 Na 511 keV sources were used in the experiments performed. We analyze the energy resolution, sensitivity, photopeak position and spatial resolution as a function of source position. An average point spread function (PSF) resolution of 2.86 and 1.12 mm FWHM for 57 Co and 22 Na respectively was observed. Within 1.2 mm from the edge of the LSO sheet, the average photopeak position change was 5%. Simulations using annihilation photon interactions from GATE and scintillation photon transport from DETECT2000, as well as utilizing a pincushion-reduction posioning algorithm, have confirmed that the positioning and energy response observed experimently at the edge of the crystal is due to optical transport near those edges

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