Prism-PET II: Second prototype of the TOF-DOI Prism-PET brain scanner with tapered crystals and inverse rendering reconstruction

Accurate PET quantification of tracer uptake in small brain structures is confounded by low sensitivity and the partial volume effect (PVE) caused by limited spatial resolution. In this study, we present the second prototype of the Prism-PET brain scanner (Prism-PET II), which overcomes the tradeoffs among sensitivity, resolution, and cost. It employs TOF-DOI capable, single-ended Prism-PET detector blocks arranged in a compact and conformal decagon geometry. Compared to our first prototype, Prism-PET II features tapered crystals with a smaller cross-section at the crystal readout interface to mitigate light leakage, thereby enhancing both TOF and DOI resolutions of the module. Additionally, interleaved multiplexing (iMUX) readouts are used, where four anodes from every other SiPM pixel are connected to the same application-specific integrated circuit (ASIC) channel. Combined with Prismatoid light guides that provide a 4-to-1 crystal-to-SiPM ratio, a total 16-to-1 crystal-to-ASIC readout ratio is achieved, substantially reducing the complexity, heat output, and cost of the scanner without compromising the performance of the detector blocks. Our imaging studies using ultra-micro hot spot and Hoffman brain phantoms demonstrate the ultra-high-resolution performance with fine structural details and the ability to resolve features as small as 0.8 mm in the axial direction, showcasing its potential to significantly improve the accuracy of PET neuroimaging in both clinical and research settings.