The numerator and denominator of the left-hand side of the Gjedde-Patlak-Rutland (GPR) equation for measurement of blood fluorine-18 fluorodeoxyglucose (F-FDG) clearance into tissue (Ki) are the standardized uptake values (SUVs) of tissue and blood, respectively. The extent to which normalized time (NT) in the GPR equation exceeds real time depends on half-time of clearance of F-FDG from blood. A literature review shows that NT is fairly constant, about 100 min at 60 min postinjection of F-FDG, in keeping with our own finding of no significant difference in maximum SUV in blood 60 min postinjection of F-FDG between 39 patients with F-FDG-avid malignancy on routine PET/CT (1.74±0.31) and 21 patients with normal PET/CT (1.79±0.32), and similar blood glucose levels (BGLs). Volume of distribution (V0) in the GPR equation is ∼0.4 ml/ml for brain and ∼0.9 ml/ml for lean liver. Using these values of V0 and an NT of 100 min, we used the GPR equation to calculate Ki from our own published values of SUVliver/SUVblood and SUVbrain/SUVblood at 60 min postinjection, obtaining 0.0045 ml/min/ml for liver and 0.036 ml/min/ml for brain at BGL of 5 mmol/l. These values for Ki at this BGL are close to literature values of Ki, which for liver and brain are ∼0.0033 and ∼0.035 ml/min/ml, respectively. We conclude, therefore, that following division with blood pool SUV, tissue SUV becomes a closer surrogate of Ki. This division also eliminates the controversy over which whole body metric to use in the calculation of SUV.