Influence of glucose challenge on 2-deoxy-2-[¹⁸F]fluoro-D-glucose small animal positron emission tomography (PET) studies in rats

Imaging of regional glucose metabolism in small animals by dynamic PET Imaging of regional glucose metabolism in small animals by dynamic PET studies using 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) provides the unique possibility to study normal physiology and pathophysiological situations in various disease models in vivo. However, plasma glucose levels and other factors influence 18F-FDG PET studies. Therefore, we examined and compared the tissue-specific 18F-FDG uptake and kinetics in rats without and with a glucose challenge. 18F-FDG kinetics was studied for one hour in anesthetized rats using a dedicated small animal PET system. The animals were injected intravenously with 18F-FDG without (control) or simultaneously with glucose (270 mg/kg body weight). PET images were reconstructed and three-dimensional regions of interest were determined for subsequent data analysis. The plasma glucose concentrations one hour after injection were similar in the control and post challenge group. Tissue-specific 18F-FDG uptake, e.g., in brain, heart and liver, tends to be lower in the post challenge group as compared to the controls. Only with increasing body weight (>250 g) post challenge plasma glucose increased. However, in the post challenge group the kinetics of 18F-FDG was different only in the first 15 min after injection when compared to the controls, but subsequently converged to control kinetics within the following 45 min. In summary, glucose challenge did not influence the tissue-specific distribution pattern of 18F-FDG due to the high glycolysis rate of the rat. On the other hand, in diabetic models, older or larger animals the effects of increased plasma glucose levels should be taken into account for interpretation of PET data.