A DOI-PET detector inserting glass plates to provide multiple spatial resolutions

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A DOI-PET detector with multiple spatial resolutions to provide high versatility for both clinical and research applications using a single camera was proposed and examined. Two layers of pixelated LYSO crystal arrays with different pixel pitches were stacked in the depth direction. The top layer was a 6 × 6 array of 2.1 × 2.1 × 10 mm3 crystals, arranged with a 2.2-mm fine pitch. The bottom layer was a 4 × 4 array of 3.2 × 3.2 × 10 mm3 crystals, arranged with a coarse 3.3-mm pitch. A Monte-Carlo simulation was conducted to estimate the glass plate thickness which allows the discrimination of each crystal position from the 2D flood histogram. In experimental measurement, we inserted 4-mm, 5-mm, and 6-mm thick glass plates between the crystal layers. These generated a unique light response for each discrete scintillator position. Light was shared more relatively when the top layer interacted with the gamma rays, whereas light sharing was reduced when the bottom layer interacted with the gamma rays. These light spreading methods allow us to extract 3D information from a 2D flood histogram. Sixteen output signals from a 4 × 4 GAPD array were multiplexed by resistive charge division networks. These were fed into the preamplifiers. The four amplified signals were digitized and were recorded into the DAQ system. By inserting the glass plates into the detectors, we acquired 2D flood histograms without the overlapping of each crystal position. The average peak-to-valley ratios of selected line profiles of a DOI-PET detector with 4-mm thick glass plate were 12.5 for the top layer and 30.8 for bottom layer. The mean energy resolution of the top layer providing high spatial resolution (the bottom layer providing moderate spatial resolution) were 14.4 ± 1.0% (13.4 ± 1.4%), 13.3 ± 1.7% (13.8 ± 0.8%), and 13.7 ± 1.6% (13.8 ± 0.9%) for the DOI-PET detector using 4-mm-, 5-mm-, and 6-mm-thick glass plates, respectively. Our results demonstrated that it is feasible to provide multiple spatial resolutions and 2-layer depth positions for the proposed DOI-PET detector using fine- and coarse-pitch crystals and inserting a glass plate between the crystal layers.