A depth of interaction PET detector using side surface readout

We investigate the potential for extracting DOI information from reading out the light distribution along two (or three) surfaces of a discrete crystal PET detector array. The concept was investigated using both Monte Carlo (GEANT4) simulations and measurements. The crystal array was composed of a 1×6 array of 4×4×22 mm
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LYSO crystals optically coupled with meltmount (N=1.7). One or two of the 4×22 mm
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sides were optically coupled to a linear array of SiPM sensors (lateral SiPMs), as was one of the 4×24 mm
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sides (backend SiPMs.) The other sides of the array were covered with reflective material. A coincidence collimated point flux was collected at regular intervals along the DOI axis of each of the six crystals. The light response function was determined for each crystal versus DOI. The simulated and experimentally measured light response functions had similar shapes. A combination of simulated and measured data analysis was used to investigate the possibility of reducing the number of lateral SiPMs. DOI positioning was excellent for the two crystals nearest the lateral SiPM arrays and for the 10 mm closest to the backend SiPM array but degraded in the two center crystals. Estimated spatial resolution was below 5 mm in 90% of the array when using the backend and one lateral array, and less than 4.5 mm throughout the array when using at least two SiPMs from both lateral arrays.