Factors affecting myocardial 2-[F-18]fluoro-2-deoxy-d-glucose uptake in positron emission tomography studies of normal humans

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Abstract
The goal of this study was to identify the anatomic and physiologic factors affecting left ventricular myocardial 2-[F-18]fluoro-2-deoxy-d-glucose (FDG) uptake and myocardial glucose utilization rates (MRGlc) in normal humans. Eighteen healthy male volunteers were studied in the fasting state (4–19 h) and 16 after oral glucose loading (100 g dextrose) with positron emission tomography (PET) and FDG. Substrate and hormone concentrations were measured in each study. The kinetics of myocardial FDG uptake were evaluated using both a three-compartment model and Patlak graphical analysis. Systolic blood pressures and rate pressure products were similar in the fasting and postglucose states. MRGlc averaged 0.24±0.17 μmol/min/g in fasting subjects and rose to 0.69±0.11 μmol/min/g after glucose loading. Phosphorylation rate constant, k3, and MRGlc were linearly related (P < 0.001). Increases in MRGIc following glucose loading were correlated with plasma glucose, insulin and free fatty acid concentrations, ratios of insulin to glucagon levels, and influx rate constants of FDG. Glucose loading improved the diagnostic image quality due to more rapid clearance of tracer from blood and higher myocardial FDG uptake. When MRGlc, glucose and insulin concentrations, and insulin to glucagon ratios exceeded 0.2 μmol/min/g, 100 mg/dl, 19 μU/ml, and 0.2 μU/pg, respectively, myocardial uptake of FDG was always adequate for diagnostic use. FDG image quality and MRGlc were similar after relatively short (6 ±2 h) and overnight (16 ± 2 h) fasting. Significant (P<0.05) regional heterogeneity of myocardial FDG uptake and MRGlc was observed in both the fasting and the postglucose studies. MRGlc and FDG uptake values in the posterolateral wall were higher than those in the anterior wall and septum. Thus, both 6-h and overnight fasts resulted in similarly low myocardial glucose utilization rates. While MRGlc and myocardial FDG uptake depended on plasma glucose, free fatty acid, and insulin concentrations, the results also suggest an additional dependency on plasma glucagon levels. Regional heterogeneities in myocardial FDG uptake and MRGlc are evident and independent of the subjects' dietary state. These regional heterogeneities need to be considered in studies of patients with cardiac disease.

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