Development and Evaluation of 0.35-mm-Pitch PET Detectors With Different Reflector Arrangements

The spatial resolutions of preclinical positron emission tomography (PET) imagers are largely determined by the size of the crystals. This study explores methods to construct PET detectors using crystals with ultrasmall cross Section for preclinical PET imagers with ultrahigh resolution. Three $16\times 16$ segmented LYSO: Ce crystal arrays were built with different reflectors and assembling techniques using $0.25\times 0.25\times 6.25\,\,{\mathrm{ mm}}^{3}$ pixels. The crystal arrays were readout by 3-mm SiPMs with a crystal-to-SiPM pixel area ratio of approximately 1:94, and the signals were recorded with custom-designed read-out electronics. Two coupling configurations were conducted. The arrays were evaluated in terms of flood histogram, energy resolution, and timing resolution. The first array, constructed with discrete LYSO crystals filled with BaSO4 reflectors, had nonuniformly distributed decoding spots in the flood histogram. The second array, constructed with enhanced specular reflector (ESR) reflectors using the slab-sandwich-slice (SSS) production method, had a distorted flood histogram. The third array, constructed with the combination of ESR and BaSO4 using the SSS production method, achieved the best flood histogram in terms of crystal spot uniformity and peak-to-valley ratio (2.80±0.53). The third array also demonstrated good energy resolution (14.89%±2.30%) and timing resolution (926.5 ps). These findings suggest that the SSS production method using the combined reflectors of ESR and BaSO4 is a potential method to construct detectors for ultrahigh-resolution PET imagers.