Feasibility study of micro-dose total-body dynamic PET imaging using the EXPLORER scanner

Objectives Current PET scanners have an axial FOV of 15-30 cm, and a typical ¹⁸F-FDG PET whole-body scan requires an injected activity of 200-400 MBq. The EXPLORER project (EXtreme Performance Long REsearch scanneR) aims to build a 2-meter long total-body PET scanner, which provides massively increased sensitivity and possesses a range of capabilities currently unavailable for whole-body dynamic imaging especially at very low radiation doses with high temporal resolution. Here we study the feasibility of micro-dose dynamic total-body PET imaging using EXPLORER.

Methods We conducted a computer simulation using the SimSET Monte-Carlo toolkit. The simulated EXPLORER system consisted of 36 axial rings with a diameter of 80 cm, each formed by 48 block detectors. Each detector consisted of a 15×15 array of 3.42×3.42×20 mm3 LYSO crystals. The axial FOV of the scanner was 196 cm. The simulated TOF resolution was 530 ps. We employed the XCAT anthropomorphic male phantom with 14 major organs and tissues. We modeled an injected activity of 10 MBq. Dynamic PET data were generated using the two-tissue compartment model with kinetic parameters taken from either the literature or clinical ¹⁸F-FDG PET patient images. Data were binned into 22 frames: 10×30s, 5×60s, 4×300s, and 3×600s; each frame was then reconstructed using the 3D TOF list-mode OS-EM algorithm and a newly developed kernel method. In this study, only true coincidences were used in the reconstruction. Finally, the kinetic parameters of major organs and tissues were estimated by nonlinear least squares fitting.

Results We obtained good image quality for all the frames, including the early 30s frames. The image quality was significantly improved by using the kernel method. The estimated kinetic parameters from the micro-dose dynamic scan showed good agreement with ground truth values.

Conclusions This study demonstrated that the EXPLORER can perform total-body dynamic PET imaging at very low radiation doses with an injected activity ~20-40 fold less than that required by current protocols.

Research Support This work was carried out under the EXPLORER consortium and was funded by NIH R01 CA170874 and a UC Davis RISE award.