INFLUENCE OF HIGH AND LAW PLASMA-INSULIN LEVELS ON THE UPTAKE OF F-18FLUORODEOXYGLUCOSE IN MYOCARDIUM AND FEMORAL MUSCLE, ASSESSED BY PLANAR IMAGING

The aim of this stud) was to optimize the metabolic conditions for pla nar myocardial fluorine-18 fluorodeoxyglucose (FDG) imaging. The effec ts of high and low insulin levels during euglycaemic clamping on myoca rdial and femoral muscle FDG uptake were compared since insulin plays a major role in glucose metabolism. FDG uptake in 11 patients was stud ied using planar scintigraphy. Patients were studied twice: in the low -dose insulin protocol (LDI), insulin was infused at a rate of 20 mU/k g per hour, starting 1 h before FDG administration, while in the high- dose insulin protocol (HDI) it was infused at a rate of 100 mU/kg per hour. Glucose infusion rate was adjusted according to frequently deter mined blood glucose levels. Somatostatin was infused to block endogeno us insulin release. Planar images were obtained from the thorax region and femoral muscles. Regions of interest were drawn over normal and a bnormal myocardial areas (based on angiographic and thallium-201 data) and over lung, liver and muscle areas. After clamping, insulin levels during LDI and HDI at t=60 were 30.6+/-13.3 and 129.6+/-30.5 mU/l res pectively (P<0.0001). Femoral muscle uptake was significantly higher d uring HDI (P<0.001). Uptake in normal and abnormal myocardial areas di d not differ between the two protocols. Heart/lung ratios (NS) and hea rt/liver ratios (P<0.05) increased during HDI. It may be concluded tha t planar FDG imaging is influenced by plasma insulin levels. The eugly caemic hyperinsulinaemic clamp technique, although more demanding, giv es an adjustable metabolic steady state without significantly altering the FDG uptake patterns in normal and abnormal myocardial regions. Th e image quality of planar FDG images improves due to lower background uptake of FDG during clamping with high plasma insulin levels.