Dynamic 2-Deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) Positron Emission Tomography Imaging of Small Laboratory Animals: Effect of Simultaneous Glucose Infusion on ¹⁸F-FDG Uptake in rats

AIM: Positron emission tomography (PET) imaging of animals provides unique possibilities to study normal physiology and pathophysiology of various disease models in vivo. ¹⁸F-FDG PET uptake measurements in regions of interest (ROIs), expressed as percentage ¹⁸F-FDG uptake of the injected dose per gram (%ID/g) of tissue, are simple and easy to obtain, especially in longitudinal studies. These ¹⁸F-FDG uptake measurements may not accurately reflect the true regional rates of glucose utilization because plasma glucose levels and other factors (like anaesthesia) can affect ¹⁸F-FDG uptake. Therefore, we examined and compared the ¹⁸F-FDG uptake and kinetics in rat plasma, brain, heart and liver under urethane anaesthesia with and without simultaneous moderate glucose application to simulate variable food uptake of the rats.
MATERIAL & METHODS: Wistar rats (203+/-41 g body weight) were anesthetized by intraperitoneal application of 1.2 g urethane kg body weight. ¹⁸F-FDG kinetics was studies using a microPET P4 (CTI Concorde Microsystems). The animals were injected intravenously with 0.5 mL ¹⁸F-FDG without (control) or with glucose (55 mg) through a tail vein. One hour after injection the animals were sacrificed and blood samples, heart, and liver were excised, weighted and the activity measured. PET images were reconstructed by 2D-ordered-subset expectation maximization (2D OSEM) algorithm. 3D regions of interest were determined for the subsequent data analysis. The time activity curves of the brain, hear and liver were derived. The curves were corrected for lag time, normalized to the injected and averaged for each organ and animal group.
RESULTS: The plasma glucose concentrations one hour after injections were similar in the control (8.7+/-1.7 mmol/L). At the end of the experiment the ¹⁸F-FDG uptake in the plasma, brain, heart and liver tends to be lower in the glucose group as compared to the controls. However, the time activity curves of the control and glucose groups in the studied organs showed significantly different shapes during the first 15 min, and converged subsequently.
CONCLUSION: A moderate glucose infusion did not influence the distribution pattern of the radiotracer in the blood plasma, heart, brain and liver one hour after injection due to the high glycolysis rate of the rat tissues. It seems to be sufficient to deprive the food of the animals one hour prior to the ¹⁸F-FDG experiments to ensure stable physiological conditions for the PET studies.