Delayed FDG Imaging: Differential Washout of FDG in Ischemic and Nonischemic Myocardium -- Delayed FDG imaging improves image quality in both diabetic and nondiabetic pts. In this study, we examined whether FDG uptake and retention differ in normal and abnormal myocardial tissue in early (-45 min) and late (-2.4 hrs)PET scans. In 24 CAD pts (21 men, 3 women, age 64+/-10), 5-10 mCi of FDG, was injected -1 hr after glucose load. For each pt the LV myocardium was divided into 17 equal regions (reg). All data were decay corrected to injection time. In 408 reg, absolute myocardial FDG activity (nCi/cc) was 426+/-274 (early) and 670+/-554 (late). The amount of arterial FDG available to the myocardium, calculated as the integral of blood FDG (nCi/cc),was 12938+/-5540 (early) and expressed as a % of available arterial blood FDG) was 3.3+/-1.5 on early and 2.2+/-1.3 on late images(p<0.001). Retention of FDG was defined as the ratio of late to early % myocardial uptake. Eight pts also underwent 0-15 water studies, allowing correction for spillover, as well as stress thallium imaging to identify ischemic regions. After spillover correction, the % myocardial uptake was 3.4+/-1.3 on early and 2.4+/-1.4 on late images (p<0.001). Early myocardial FDG uptake did not differ among the normal (n=30), ischemic (n-38), and irreversible thallium reg. However, with late imaging, myocardial FDG retention was significantly lower in ischemic (58+/-16%)when compared to normal (69+/-18%, p<0.01) and irreversible (73+/-24%,p<0.001)reg . These data suggest that k4 (conversion of FDG- 6-phosphate to FDG) or washout of FDG from interstitium plays an important role in late imaging and that ischemic regions show greater net loss of FDG than other regions. - fluorodeoxyglucose (FDG), thallium, positron emission tomography (PET) - Human Subjects
