Ultra-low-activity total-body dynamic PET imaging allows equal performance to full-activity PET imaging for investigating kinetic metrics of ${}^{18}$F-FDG in healthy volunteers

To investigate the feasibility of ultra-low-activity total-body positron emission tomography (PET) dynamic imaging for quantifying kinetic metrics of 2-[${}^{18}$F]-fluoro-2-deoxy-D-glucose (${}^{18}$F-FDG) in normal organs and to verify its clinical relevance with full-activity imaging. Dynamic total-body PET imaging was performed in 20 healthy volunteers, with eight using full activity (3.7 MBq/kg) of ${}^{18}$F-FDG and 12 using 10× activity reduction (0.37 MBq/kg). Image contrast, in terms of liver-to-muscle ratio (LMR), liver-to-blood ratio (LBR), and blood-to-muscle ratio (BMR) of radioactivity concentrations were assessed. A two-tissue compartment model was fitted to the time-to-activity curves in organs based on regions of interest (ROIs) delineation using PMOD, and constant rates (k${}_1$, k${}_2$, and k${}_3$) were generated. Kinetic constants, corresponding coefficients of variance (CoVs), image contrast, radiation dose, prompt counts, and data size were compared between full- and low-activity groups. All constant rates, corresponding CoVs, and image contrast in different organs were comparable with none significant differences between full- and ultra-low-activity groups. PET images in the ultra-low-activity group generated significantly lower effective radiation dose (median, 0.419 vs. 4.886 mSv, P < 0.001), reduced prompt counts (median, 2.79 vs. 55.68 billion, P < 0.001), and smaller data size (median, 71.11 vs. 723.18 GB, P < 0.001). Total-body dynamic PET imaging using 10× reduction of injected activity could achieve relevant kinetic metrics of ${}^{18}$F-FDG and comparable image contrast with full-activity imaging. Activity reduction results in significant decrease of radiation dose and data size, rendering it more acceptable and easier for data reconstruction, transmission, and storage for clinical practice.