Intercrystal Scatter Rejection for Pixelated PET Detectors

High-resolution positron emission tomography (PET) scanners often use pixelated scintillator arrays with lightsharing for the detection of gamma rays. The aim of this paper is to enhance the spatial re.solution of such a pixelated scintillator detector by filtering out events with multiple interactions of gamma rays in the scintillator based on the measured light distributions. To develop and evaluate such enhancements in spatial resolution, we measure the point spread function (PSF) of our detector directly using a thinly collimated gamma ray beam setup, and then later verify their benefits on a full preclinical PET system with a hotrod phantom. The scintillator detector comprises a 30 × 30 × 12 mm3lutetium-yttrium oxyorthosilicate array with a pitch of 1 mm coupled to a digital silicon photomultiplier array via a 2-mm lightguide. We use a center of gravity algorithm for the crystal identification; however, the proposed filters are independent of the crystal identification algorithm. Investigating a single detector with our collimated gamma beam, we reject 15% of the events as multiple interaction while improving the crystal identification efficiency from 60.0% to 68.3% and the 90th-percentile diameter of the PSF from 7.88 to 3.98 mm. On system level, we analyze a line profile through two different rod sizes in a hotrod phantom. The filters reject 32% of the coincidences and increase the peak-to-valley ratio by 8% (0.9-mm rods) and by 18% (1.2-mm rods).