Optimization of TOF and DOI Performance in a Multi-Resolution Detector for Brain-dedicated PET

Brain-dedicated positron emission tomography (PET) systems require detectors with high spatial resolution, depth-of-interaction (DOI) resolution, and time-of-flight (TOF) resolution. This work presents the development and optimization of a multi-resolution detector module for brain PET imaging, with a focus on enhancing DOI and TOF performance. The detector module consists of four detector blocks, each featuring a two-layer lutetium yttrium oxyorthosilicate (LYSO) crystal array with different pixel sizes (top layer: 16 × 16 array of 1.53 × 1.53 × 5 mm3 crystals; bottom layer: 8 × 8 array of 3 × 3 × 15 mm3 crystals), forming an effective area of 51.6 × 51.6 mm2. To improve DOI resolution, we introduced a q-value method which achieved a DOI resolution of 3.03 mm for the bottom layer crystals. TOF resolution was optimized through timing correction techniques incorporating DOI information and multiple timestamps. For top layer events, the event time was determined using a charge-integration (QDC)-weighted average of the first three timestamps. For bottom layer events, a joint pmax&tdoi correction was applied following a QDC-4th power weighted average of the first three timestamps. The coincidence time resolution (CTR) achieved 442 ps for top-top, 370 ps for top-bottom, and 259 ps for bottom-bottom coincidences. Removing inter-crystal scatter (ICS) events from the bottom layer further improved the bottom-bottom CTR to 245 ps. The intrinsic spatial resolution (ISR) reached 0.93 mm for the top layer and 1.77 mm for the bottom layer after ICS events removal. By achieving high DOI, CTR and ISR, this detector module demonstrates significant potential for integration into next-generation, high-performance brain-dedicated PET scanners.