Abstract

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 a 1 x 8 array of pixelated lutetium–yttrium oxyorthosilicate (LYSO) crystals, each measuring 3.1 x 2.1 x 20mm³ with a pitch of 3.2 mm, coupling via a high-refractive-index adhesive (n = 1.7) to a monolithic LYSO slab of 25.5 x 1 x 20mm³. 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 of 4.0 ± 0.5mm, an average energy resolution of 11.7% ± 0.9%, an intrinsic spatial resolution of 1.7 mm along the layer-stacking direction and 2.0 ± 0.1mm 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.

Title

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

Authors

Yangyang Zhao, Hang Yang, Wenjie Huang, Xiaoqin Zhang, Xiaolong Jiang, Ming Niu, Xiangtao Zeng, Wen He, Qingyang Wei and Zheng Gu*

Journal Information

Physics in Medicine & Biology (2026)

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