Development and Initial Evaluation of 3D-printed High Resolution Brain Phantom for PET

Phantoms are essential for assessing PET system performance, but most existing brain phantoms do not provide the anatomical fidelity required for the next-generation high-resolution PET systems. To address this limitation, we developed HYDRA-OL (HYDrodynamically filled Realistic Anatomy of the Occipital Lobe) phantoms using high-resolution 3D printing based on the BigBrain atlas. In this study, two phantom types were created, HYDRA-OL_G (gray matter only) and HYDRA-OL_GW (gray and white matter), enabling contrast modulation between gray matter (GM) and white matter (WM). Precise anatomical fidelity and repositioning accuracy were confirmed via CT. A custom closed-loop filling apparatus ensured efficient and reproducible phantom preparation. Residual air in the phantom after 15 minutes was estimated to be less than 0.01% of the fillable space. To compare spatial resolution between scanners, the HYDRA-OL_G phantom was imaged on four different PET systems (NeuroEXPLORER (NX), HRRT, Vision, and Focus220), with NX and Focus showing superior spatial resolution compared to the other two systems. To generate variable GM:WM contrast, list mode datasets obtained on the NX for both HYDRA-OL_G and HYDRA-OL_GW phantoms were down-sampled and merged to form one list mode data. Reconstructed images were successfully produced with GM:WM contrast ratio of 4:1, 2:1, and 4:3. Overall, the HYDRA phantom platform is a versatile tool for accurately representing human brain anatomy. It is likely to be more useful than previous phantoms for evaluating image resolution and optimizing reconstruction parameters for next-generation brain PET systems.