High-resolution dual-ended readout PET detectors based on 0.5 mm pitch LYSO arrays with various reflectors

High-resolution and high-sensitivity small-animal positron emission tomography (PET) scanners are essential non-invasive functional imaging tools in preclinical research. To develop small-animal PET scanners with uniform and high spatial resolution across the field-of-view, PET detectors capable of providing good depth-of-interaction (DOI) information are critical. Dual-ended readout detectors based on lutetium-yttrium oxyorthosilicate (LYSO) arrays with fine pitch represent a promising approach, wherein the choice of inter-crystal reflector significantly impacts the detector performance. Toray E60, with a 50 µm thickness, has been used for over two decades as an inter-crystal reflector for fabricating LYSO arrays used in dual-ended readout detectors. However, the Toray E60 has recently been discontinued.

This study aims to identify an optimal alternative to the Toray E60 reflector, facilitating the continued development of dual-ended readout detectors for high-resolution and high-sensitivity small-animal PET scanners.

Five dual-ended readout detectors based on 10 × 10 LYSO arrays were constructed and evaluated. These LYSO arrays employed different reflectors: Toray E60 with 50 µm thickness, Barium sulfate (BaSO₄) with 80 µm thickness, and Toray E20 with thicknesses of 40, 52, and 76 µm. All LYSO arrays featured the same pitch of 0.5 mm and thickness of 20 mm. Two linearly-graded silicon photomultipliers (LG-SiPMs) served as photodetectors. The performance of the five detectors in terms of crystal identification ability, energy resolution, coincidence timing resolution (CTR), and DOI resolution was comprehensively compared.

Among the five reflectors, the detector based on the LYSO array with the 52 µm thick Toray E20 reflector exhibited the best crystal identification ability and achieved an energy resolution of 20.2 ± 3.8%, a DOI resolution of 2.07 ± 0.48 mm, and a CTR of 882 ± 38 ps. Conversely, the detector based on the LYSO array with the 50 µm thick Toray E60 reflector showed an energy resolution of 22.0 ± 3.3%, a DOI resolution of 1.88 ± 0.25 mm, and a CTR of 833 ± 32 ps.

The Toray E20 reflector with a thickness of 52 µm represents a viable alternative to the discontinued Toray E60 with a 50 µm thickness. It is suitable for fabricating finely pitched and thick LYSO arrays used in dual-ended readout detectors to develop high-resolution and high-sensitivity small-animal PET scanners.