Parametric analysis of dynamic long axial field-of-view 18F-FDG PET/CT studies

Large-axial field of view (LAFOV) PET/CT systems have improved whole-body dynamic 18F-FDG imaging, enabling improved quantitative assessment of tracer kinetics. While non-linear regression (NLR) models remain the most unbiased approach, voxel-wise implementation can suffer from convergence problems, resulting in increased uncertainties. Parametric methods such as Patlak, Generalized Patlak (gPatlak), basis function method irreversible (BFM-I), and basis function method reversible (BFM-R) offer alternatives for estimating parametric Ki and, if applicable, K1 values. This study aims to determine the most suitable parametric approach for quantifying 18F-FDG kinetics in various healthy organs and tumour lesions using a LAFOV PET/CT system. Thirteen patients with malignancies underwent 70-minute dynamic 18F-FDG PET/CT scans on a LAFOV PET/CT system after receiving an intravenous bolus injection of 3.0 MBq/kg. First, the data were split on preference for irreversible (2T3k) or reversible (2T4k) kinetics. Ki from Patlak (t* = 30 min) and BFM-I (t* = 0 min) were compared with those derived from the 2T3k model. Ki from gPatlak (t* = 10 min) and BFM-R (t* = 0 min) were compared with those obtained with 2T4k. Ki and K1 values were extracted from the brain, liver, spleen, lung, kidney, upper leg muscle, and up to three tumour lesions per patient. The liver, myocardium, lungs, and muscle favoured the irreversible 2T3k model, while preferences for the kidney, brain, spleen, and tumour lesions varied across patients. For organs preferring irreversible kinetics, BFM-I (R = 0.99) outperformed Patlak (R = 0.97) in Ki agreement with the 2T3k model. For reversible kinetics, BFM-R (R = 0.95) showed better correspondence compared to gPatlak (R = 0.90) with the 2T4k model. K1 obtained by BFM-I and BFM-R also strongly correlated with those derived from compartment models. LAFOV PET/CT systems enable accurate whole-body kinetic modelling of 18F-FDG uptake. BFM-I and BFM-R demonstrated the highest agreement with the compartment models and are recommended when full dynamic PET scans are feasible, offering accurate Ki as well as K1 estimations across healthy organs and tumour lesions.