Wen He's latest paper A multi-resolution TOF-DOI detector for human brain dedicated PET scanner was published in Physics in Medicine & Biology. In this paper, the authors propose an innovative dual-layer, multi-resolution PET detector design that simultaneously achieves high spatial resolution, high DOI (Depth of Interaction) resolution, high TOF (Time-of-Flight) resolution, and high detection efficiency.

As illustrated in Figure 1, the upper layer utilizes crystal pixels with a smaller cross-sectional size of 1.53mm to achieve higher spatial resolution. The middle layer introduces light guides for optical sharing between crystals to achieve high DOI resolution. The lower layer employs crystal pixels with a larger cross-sectional size of 3.0mm, coupled 1:1 with silicon photomultipliers (SiPMs) for readout, to reduce scintillation light detection time jitter and enhance TOF resolution. The total crystal thickness is 21mm, ensuring high detection efficiency.

Utilizing the distinct characteristics of scintillation light distribution in the upper and lower layers, the authors first employ Convolutional Neural Network (CNN) to differentiate gamma events occurring in the upper or lower crystal layers. This approach yields clear crystal decoding images and energy spectra. By mathematically characterizing the scintillation light distribution, the study achieves the capability to distinguish at least three interaction depths in the lower layer crystals, resulting in an average DOI resolution of 4.1mm. Finally, using the obtained DOI and energy information, the triggering time of gamma events is corrected and optimized. The coincidence events of the two detector's lower layer crystals achieve a TOF resolution better than 300 ps.

This research realizes an innovative detector with high spatial resolution, high DOI resolution, high TOF resolution, and high detection efficiency. It establishes a core technological foundation for the development of the next generation of high spatial resolution, high sensitivity, human brain-specific PET systems.

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A multi-resolution TOF-DOI detector for human brain dedicated PET scanner