Lumped constant for [18F]fluorodeoxyglucose in skeletal muscles of obese and nonobese humans

1 Turku Positron Emission Tomography Center and 2 Lundberg Laboratory for Diabetes Research, Department of Internal Medicine, University of Gothenburg, 41345 Gothenburg, Sweden; and 3 Department of Medicine, University of Turku, F-20520 Turku, Finland Quantitative 2-[ 18 F]fluoro-2-deoxy- D- glucose ([ 18 F]FDG) positron emission tomography (PET) has been widely used to calculate glucose utilization in skeletal muscle. FDG-PET results depend partly on the lumped constant (LC), which accounts for the differences in the transport and phosphorylation between [ 18 F]FDG and glucose. In this study, we estimated the LC for [ 18 F]FDG directly in normal and in insulin-resistant obese subjects by combining FDG PET with the microdialysis technique. Eight obese [age 29.4 ± 1.0 yr, body mass index (BMI) 33.6 ± 1.0 kg/m 2 ] and eight nonobese (age 25.0 ± 1.0 yr, BMI 23.1 ± 1.0 kg/m 2 ) males were studied during euglycemic hyperinsulinemia (1 mU · kg 1 · min 1 for 150 min). Muscle blood flow was measured using 15 O-labeled water and PET. Muscle [ 18 F]FDG uptake (rGU FDG ) was calculated with Patlak graphic analysis. Interstitial glucose concentration of the quadriceps femoris muscle was measured simultaneously with [ 18 F]FDG scanning using microdialysis. Muscle glucose uptake (by microdialysis, rGU MD ) was calculated by multiplying glucose extraction by regional muscle blood flow. A significant correlation was found between rGU MD and rGU FDG ( r = 0.78, P