Practice question

Positron emission tomography with fluorodeoxyglucose quantifies glucose metabolism, so systemic glucose handling critically influences diagnostic quality. In postprandial state, elevated blood glucose competes directly with tracer for transporter uptake, while insulin surge drives FDG into skeletal muscles and fat, increasing diffuse background and obscuring cerebral or tumor hypermetabolism. Maintaining 4-6 hour fasting keeps serum glucose and insulin low, maximizing target-to-background contrast and enabling standardized uptake value quantification. Magnetic resonance, EEG and diffusion tensor imaging do not use glucose-dependent tracers requiring such metabolic preparation for accuracy.