Detector Innovation for PET: Demonstrated 1‑Mm Rod-Resolution Brain PET and Extension to Whole‑Body PET
Abstract
Purpose
The spatial resolution of current PET systems, typically around 4 mm, remains far from the theoretical limit of 1-2 mm primarily determined by photon non‑collinearity. Achieving PET resolution closer to that of CT and MRI would enable earlier disease detection and improve treatment planning. At AAPM2025, we reported a one‑ring brain PET prototype using our Crosshair Light‑Sharing (CLS) detectors, which provide depth‑of‑interaction (DOI) capability along the scintillation crystals. The aim of this study is to develop a full‑scale seven‑ring brain PET prototype, CLS‑7, and investigate the feasibility of applying CLS detectors to whole‑body PET imaging.
Methods
CLS‑7 incorporates 252 CLS detectors, resulting in a ring diameter of 29.6 cm and an axial field‑of‑view of 18.5 cm. Each detector consists of Fast‑LGSO crystals (1.45 × 1.45 × 15 mm³) coupled to a 3.2 mm‑pitch silicon photomultiplier array read out by the PETsys system. Rod‑phantom imaging was compared to VRAIN, our hemispherical brain PET system commercialized in Japan in 2022, that uses 4.0 mm crystals without DOI capability. For potential whole‑body PET applications, Geant4 simulations were conducted for 70 cm‑diameter PET systems: one using CLS detectors and one using conventional 4.0 mm crystals without DOI.
Results
CLS‑7 resolved rods as small as 1.0 mm, whereas VRAIN could resolve down to 2.2 mm. The finer crystal pitch and DOI capability contributed to the superior spatial resolution of CLS‑7. Time‑of‑flight performance was similar between systems (264 ps for CLS‑7 vs. 229 ps for VRAIN). In the whole‑body PET simulations, the CLS‑based system clearly separated 1.35 mm rods, while the conventional detector was limited to 2.4 mm.
Conclusion
We developed a full‑scale seven‑ring brain PET system, CLS‑7, and demonstrated a rod resolution of 1 mm. Simulation results indicate that CLS detectors hold strong potential for whole‑body PET imaging, achieving approximately 1.35 mm rod resolution.