An optically coupled hybrid semi-monolithic PET detector for simplified DOI and position decoding.

Objective.Positron emission tomography (PET) detectors that encode depth-of-interaction (DOI) while achieving high timing and energy resolution are essential for long axial field-of-view (FOV) clinical PET systems. In this work, we propose an optically coupled hybrid semi-monolithic detector design, in which a pixelated scintillator array is coupled to a monolithic scintillator slab using optical adhesive. This design enables DOI capability while simplifying positioning calibration and preserving high timing and energy performance.Approach.Based on this concept, a prototype detector composed of a single-layer hybrid structure was fabricated and comprehensively evaluated. The prototype consists of aarray of pixelated lutetium-yttrium oxyorthosilicate (LYSO) crystals, each measuringwith a pitch of 3.2 mm, coupling via a high-refractive-index adhesive () to a monolithic LYSO slab of. The interface surfaces between the pixelated array and the monolithic slab were unpolished. The detector was read out using a TOFPET2 application-specific integrated circuit (ASIC).Main results.Experimental results show clearly separated pseudo-pixel event clusters in the flood image, enabling planar event positioning using a conventional energy-weighted average method. Using a 400-600 keV energy window, the detector achieved an average DOI resolution ofmm, an average energy resolution of, an intrinsic spatial resolution of 1.7 mm along the layer-stacking direction andmm along the pixelated array direction, and a coincidence timing resolution of 281 ps.Significance.These results demonstrate that the proposed optically coupled hybrid semi-monolithic detector balances detector performance (including DOI, timing and energy resolution) with calibration complexity. The design offers a promising detector solution for long axial FOV clinical PET systems.