Estimating the amount of FDG uptake in physiological tissues

It 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-[(18)F]fluoro-D-glucose (18FDG) uptake amount in physiological tissues that may show an intense uptake in current clinical practice.

A 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.

P ≅ 0.17*exp(-λt(acq))*TLG/W, where λ is the (18)F physical decay constant, t(acq) 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.

A 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.