Final Answer:
Glucose loading is performed in FDG PET to suppress physiological uptake of FDG by normal tissues, particularly the brain, and enhance the detection sensitivity for pathological lesions.
Step-by-step explanation:
In FDG PET imaging, FDG (Fluorodeoxyglucose), a glucose analog, is used as a radiotracer to visualize metabolic activity in tissues. However, normal tissues, especially the brain, exhibit high physiological uptake of glucose, which can interfere with the accurate detection of abnormal metabolic activity in other regions. To overcome this, patients are often subjected to glucose loading – the administration of a high-carbohydrate diet or an intravenous glucose solution before FDG injection. This results in increased insulin levels and subsequent reduction of physiological FDG uptake by normal tissues. The rationale behind this approach is based on the competitive inhibition of FDG uptake by normal cells, effectively "blocking" their avidity for the radiotracer.
The competitive inhibition is explained by the fact that both glucose and FDG utilize the same glucose transporters (GLUTs) for cellular uptake. When glucose levels are elevated, due to loading, the transporters become saturated with glucose, leading to decreased uptake of FDG. This selective reduction in normal tissue FDG uptake enhances the visibility of abnormal metabolic processes, such as cancer cells that often have increased glucose metabolism.
Therefore, glucose loading is a strategic maneuver to improve the diagnostic accuracy of FDG PET imaging by minimizing interference from physiological glucose uptake in normal tissues, allowing for more precise localization and characterization of pathological lesions.