Estimating the amount of FDG uptake in physiological tissues

IntroductionIt is known that for a fixed amount of injected tracer, the amount available for a tissue of interest will be less if other tissues show intense uptake. The aim of this study was to estimate the magnitude of 2-deoxy-2-[18F]fluoro-d-glucose (18FDG) uptake amount in physiological tissues that may show an intense uptake in current clinical practice.MethodsA formula was established providing an estimate of the percentage of injected 18FDG molecules (P; in %) that are irreversibly trapped in an 18FDG-positive tissue during a PET examination.ResultsP ≅ 0.17*exp(−λtacq)*TLG/W, where λ is the 18F physical decay constant, tacq is the injection-acquisition time delay, TLG is total lesion glycolysis (g) and W is the patient weight (kg). The magnitude of P was calculated in two patients showing an intense uptake in brown fat, myocardium and bowels: 0.5, 3.5, and 4.2% respectively.ConclusionsA formula is available to quickly estimate the amount of 18FDG uptake in tissues. We suggest that the accumulation of different physiological uptakes may actually affect SUV quantification in a tissue of interest.