Calculating an estimate of tissue integrated activity in 18F-FDG PET imaging using one SUV value

A kinetic model analysis was recently proposed to estimate the 18F-fluorodeoxyglucose (18F-FDG) integrated activity in an arbitrary tissue that uses tracer uptake and release rate constants. The aim of the current theoretical paper was to estimate 18F-FDG integrated activity using one standardized uptake value (SUV).

A further kinetic model analysis allowed us to derive an analytical solution for integrated activity determination, involving both irreversible and reversible trapping. It only uses SUV, which is uncorrected for 18F physical decay (SUVuncorr, in g.mL-1) and is assessed about its peak value. Measurement uncertainty of the estimate was also assessed.

In a tissue (volume V, in mL) that irreversibly traps 18F-FDG, the total number of disintegrations can be estimated as: ÃC = 162 * 105 * SUVuncorr * V * ID / W (ID, injected dose, in MBq; W, patient's weight, in kg), where SUVuncorr is a mean over V and is assessed between 55 and 110 min after tracer injection. The relative uncertainty ranges between 18% and 30% (the higher the uptake, the lower the uncertainty). Comparison with the previous Zanotti-Fregonara's model applied to foetus showed less than 16% difference. Furthermore, calculated integrated activity estimates were found in good agreement with Mejia's results for healthy brain, lung and liver that show various degrees of tracer trapping reversibility and various fractions of free tracer in blood and interstitial volume.

Estimation of integrated activity in an arbitrary tissue using one SUV value is possible, with measurement uncertainty related to required assumptions. A formula allows quick estimation that does not underestimate integrated activity so that it could be helpful in circumstances such as accidental exposure, or for epidemiologic purposes such as in patients having undergone several examinations.