A two-compartment model is used to derive the tissue time-activity curve of 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG). At the later phase of the 18F-FDG activity in the tissue, the model leads to a method which allows the assessment of the 18F-FDG uptake rate constant. The proposed method is both compared with the standard uptake value (SUV) method and with Patlak's graphical analysis.