Abstract
201
Objectives: To determine the effects of dietary state and insulin on the uptake and tissue kinetics of F-18 deoxyglucose (FDG) in myocardium, brain and skeletal muscle in anesthetized mice.
Methods: In 23 CL57BL/6 isoflurane anesthetized mice (28.9±4.1 g), FDG (18.1±5.5MBq) was injected intravenously and microPET data acquired in list-mode for 60 minutes. Seven mice were non-fasted, five were fasted overnight, another 6 non-fasted and 5 fasted mice received subcutaneous insulin(2IU/kg) immediately prior to FDG. Blood was sampled serially from an arterialized tail vein for measurements of FDG and glucose concentrations. Image data were reconstructed with filtered back projection and CT-derived attenuation correction into 30 frames. Volumes of interests (VOI) were assigned to myocardium, brain and skeletal muscle of a foreleg. Standardized uptake values (SUV) were estimated from the last 15 minute image and uptake rate constants (Ki) by graphical analysis from the four to 60 minute tissue activity and blood FDG concentrations.
Results: In myocardium, SUV was significantly lower in fasted than in non-fasted mice but did not change with insulin in non-fasted mice [table]. Blood glucose levels were stable in fasted and non-fasted mice and declined after insulin treatment. Insulin also accelerated the blood FDG clearance significantly. Myocardial Ki was significantly lower in fasted than in non-fasted animals and increased significantly with insulin. In skeletal muscle, SUV and Ki tended to be higher in insulin treated mice. In the brain, SUV and Ki were highest in both fasted groups. Despite declining glucose levels due to insulin, graphical analysis of myocardial Ki values always yielded high correlation coefficients (r2 > 0.93).
Conclusions: As expected insulin increased, fasting decreased myocardial and muscle Ki which could be demonstrated in vivo by dynamic microPET. Metabolic changes in heart and mucle were more apparent in Ki values than in SUVs, since changes of input function were accounted for in Ki by kinetic modeling. Changing blood glucose levels during the study did not affect the use of the graphical analysis of myocardial FDG uptake rates likely because of high transport capacities.
- Society of Nuclear Medicine, Inc.