Author: Go Akamatsu, Yuma Iwao, Kurumi Narita, Hideaki Tashima, Taiga Yamaya, Eiji Yoshida 👨🔬
Affiliation: National Institutes for Quantum Science and Technology 🌍
Purpose: In brain positron emission tomography (PET), higher spatial resolution is better for visualizing detailed structures such as small nuclei and the layered structure of the cerebral cortex. Therefore, the world’s first hemispherical brain PET, VRAIN, was developed by using a 4.2 mm-pixel detector with a 229 ps time-of-flight (TOF) resolution, and achieved a rod separation of 2.2 mm. Following this development, the aim of this study was to design a next-generation hemispherical brain-PET with 1 mm resolution, which is close to the theoretical limit of the spatial resolution in brain PET.
Methods: A new 1.6 mm-pixel detector with both TOF and depth-of-interaction (DOI) measurement capability was developed. The Lu-based scintillators with a quarter cross section of the photodetector element formed U-shaped optical paths toward the east, west, north and south, respectively. After developing a one-ring prototype with 36 detectors and confirming its basic performance, Geant4 simulation of a full-scale hemispherical geometry with 242 detectors was performed.
Results: Using a Fast-LGSO crystal sized at 1.45 x 1.45 x 15 mm3 and a silicon photomultiplier array of a 3.2 mm pixel pitch read out by the PETsys system, a TOF resolution better than 300 ps and the 3-layer DOI discrimination were achieved in the one-ring prototype. An ultra-micro hot phantom was measured, and all 1.0 mm-rods and some 0.75 mm rods were resolved. In the full-scale simulation, the next generation hemispherical geometry with the same dimensions as VRAIN was modeled and compared with VRAIN, which was also modeled in the simulation. For the BigBrain phantom with full data correction (normalization, attenuation correction, random correction and scatter correction), more detailed visualization of the cortex was observed with the new detector.
Conclusion: The feasibility of the next generation hemispherical brain PET with 1 mm resolution was confirmed through experiment and simulation.