Detector design for a high-resolution and high-sensitivity breast-dedicated multiplexed PET ( <i>m</i> PET) scanner

<i>Objective</i>. We are developing a high-resolution, high-sensitivity breast-dedicated PET scanner that can image the distribution of multiple tracers simultaneously, referred to as multiplexed PET (<i>m</i>PET). This requires the detector to have high intrinsic spatial resolution and detection efficiency, as well as resolve photon depth-of-interaction (DOI).<i>Approach</i>. The detector array design comprises a novel trapezoidal shape configuration with scintillation crystal rod elements of different lengths to enable adequate intrinsic detection efficiency for prompt gamma ray photons (>511 keV) in addition to 511 keV photons, which is also practical to fabricate and assemble. The LYSO element lengths range from 5 mm to 35 mm, with a 1.28 mm pitch, read out by a multi-pixel photon counter (MPPC) array with a 3 mm pixel size. A light-sharing approach, combined with unpolished crystal surfaces and top-side light guides, enables DOI encoding. A prototype detector module was experimentally evaluated for flood image/crystal element separation, energy, DOI, and detector timing resolution. Measurements were performed under both side-irradiation and top-irradiation setups to assess the detector's performance across different interaction positions.<i>Main results</i>. The prototype detector flood image successfully resolved crystal elements even for 35 mm length crystals. DOI resolutions in full width at half maximum measured 4-6 mm for crystal lengths ranging from 10 mm to 30 mm and 7-8 mm for the 35 mm crystal length. Energy resolutions varied from 13% to 28%, with degradation observed at positions farther from the MPPC array plane. Detector time resolution values ranged from 330 ps to 660 ps.<i>Significance.</i>This work introduces a novel, single-ended readout, DOI-capable detector design that optimizes sensitivity while maintaining high spatial resolution for a breast-dedicated<i>m</i>PET system, utilizing a unique trapezoidal crystal array and light-sharing DOI encoding designs. Additionally, this design offers a scalable approach that can be adapted to other high-performance PET systems.