Monolithic U-shaped crystal design for TOF-DOI detectors: a flat top versus a tapered top

For brain-dedicated positron emission tomography (PET) scanners, depth-of-interaction (DOI) information is essential to achieve uniform spatial resolution across the field-of-view (FOV) by minimizing parallax error. Time-of-flight (TOF) information can enhance the image quality. In this study, we proposed a novel monolithic U-shaped crystal design that had a tapered geometry to achieve good coincidence timing resolution (CTR) and DOI resolution simultaneously. We compared a novel tapered U-shaped crystal design with a conventional flat-top geometry for PET detectors. Each crystal had outer dimensions of 5.85 × 2.75 × 15 mm³, with a 0.2 mm central gap forming physically isolated bottom surfaces (2.85 × 2.75 mm²). The novel U-shape crystal design with a tapered top roof resulted in the best CTR of 201 ± 3 ps, and DOI resolution of 3.1 ± 0.6 mm, which were better than flat top geometry. In the next study, we plan to optimize the crystal surface treatment and reflector to further improve the CTR and DOI resolution.