Estimation of kinetic constants in double injection FDG-PET studies: application in neurology and oncology

In order to characterize physiological cerebral activation or tissue response to a treatment, at least two FDG-PET studies are mandatory. In this work, a study of one hour duration with two injections at 30 min apart is reported. The separation of the two input curves (IC) consisted of fitting the blood curve corresponding to the first injection using spectral analysis, then estimating the second blood curve by removing the remnant of the first. Tissue time activity curves (tTAC) were fitted for the first 30 min using the first IC and were extrapolated till 60 min. This extrapolated part was removed from the tissue response to the second injection before being fitted using the second IC. Other data were obtained for simple injection from which regional cerebral metabolic rates for glucose (rCMRGlu) estimated from 0-30 min were compared to those obtained from 0-60 min. Maximal rCMRGlu differences in double injection with activation were found to be on the average four times higher than those from 0-30 and 0-60 min baseline simple injection. The method is expected to be more accurate to observe drug uptake or tumor response to a treatment.