CORRECTION OF SPILLOVER RADIOACTIVITIES FOR ESTIMATION OF THE BLOOD TIME-ACTIVITY CURVE FROM THE IMAGED LV CHAMBER IN CARDIAC DYNAMIC FDG PET STUDIES

In dynamic cardiac PET FDG studies for measurement of myocardial metab olic rate of glucose (MMRGlc), the plasma FDG time-activity curve (inp ut function) is commonly obtained from the left ventricular (LV) regio n on the PET images. The input function is contaminated by spillover o f radioactivity from the surrounding myocardium and this could cause s ignificant error in the estimated MMRGlc. In this study, we determined the effect of myocardial to blood pool spillover on MMRGlc and develo ped a method to correct for this spillover of activity. The method is based on a reformulation of the FDG model equation in terms of the spi llover contaminated input function that includes both the myocardium t o blood pool and blood pool to myocardium spillover fractions as varia ble parameters (F-mb and F-bm) The reformulated model equation can be used to fit the global myocardial tissue activity curve to estimate F- mb and thus yields a spillover corrected input function. The MMRGlc es timate with the corrected input function was within 95% of the true va lue (compared to 85% using the uncorrected input function) in a set of computer simulation studies. Dynamic PET FDG data were obtained in ei ght human studies and blood samples were obtained during the study. As compared to the results with the uncorrected input function, the esti mates of k(4) by the new method were reduced by 69% into a range consi stent with in vitro results. The method is effective in correcting F-m b spillover and leads to more accurate estimates of MMRGlc. The method also allows larger regions of interest (up to 150 mm(2)) to be drawn over the Lv in dynamic PET images, thereby reducing the noise level in the input function.