The most accurate way to estimate the glucose metabolic rate (or its influx constant) from (18)F-FDG PET is to perform a full kinetic analysis (or its simplified Patlak version), requiring dynamic imaging and the knowledge of arterial activity as a function of time. To avoid invasive arterial blood sampling, a simplified kinetic analysis (SKA) has been proposed, based on blood curves measured from a control group. Here, we extend the SKA by allowing for a greater variety of arterial input function (A(t)) curves among patients than in the original SKA and by accounting for unmetabolized (18)F-FDG in the tumor.
Methods: Ten A(t)s measured in patients were analyzed using a principal-component analysis to derive 2 principal components describing most of the variability of the A(t). The mean distribution volume of (18)F-FDG in tumors for these patients was used to estimate the corresponding quantity in other patients. In subsequent patient studies, the A(t) was described as a linear combination of the 2 principal components, for which the 2 scaling factors were obtained from an early and a late venous sample drawn for the patient. The original and extended SKA (ESKA) were assessed using fifty-seven (18)F-FDG PET scans with various tumor types and locations and using different injection and acquisition protocols, with the K(i) derived from Patlak analysis as a reference.
Results: ESKA improved the accuracy or precision of the input function (area under the blood curve) for all protocols examined. The mean errors (±SD) in K(i) estimates were -12% ± 33% for SKA and -7% ± 22% for ESKA for a 20-s injection protocol with a 55-min postinjection PET scan, 20% ± 42% for SKA and 1% ± 29% for ESKA (P < 0.05) for a 120-s injection protocol with a 55-min postinjection PET scan, and -37% ± 19% for SKA and -4% ± 6% for ESKA (P < 0.05) for a 20-s injection protocol with a 120-min postinjection PET scan. Changes in K(i) between the 2 PET scans in the same patients also tended to be estimated more accurately and more precisely with ESKA than with SKA.
Conclusion: ESKA, compared with SKA, significantly improved the accuracy and precision of K(i) estimates in (18)F-FDG PET. ESKA is more robust than SKA with respect to various injection and acquisition protocols.