[18F]fluorodeoxyglucose uptake in tumors: kinetic vs. steady-state methods with reference to plasma insulin

[18F]Fluorodeoxyglucose (FDG) uptake in noncerebral tumors is commonly reported as tissue radioactivity concentration normalized to injected dose and body weight. We studied the feasibility of this approach by imaging 68 tumors in 46 oncologic patients with dynamic FDG-PET and compared kinetic and static methods of quantitation of FDG uptake. Further, the effect of plasma glucose and insulin concentration on the obtained quantitative indexes was analyzed in all patients. The metabolic rate for FDG was strongly associated with normalized uptake value adjusted for injected dose (r = 0.92, p < 0.0001), dose and patient weight (r = 0.91, p < 0.0001), and dose and body surface area (r = 0.94, p < 0.0001). The FDG uptake was not related to plasma glucose concentration under euglycemic (< or = 6.5 mmol/L) conditions, but was low in two diabetic patients with overt hyperglycemia. Hyperinsulinemia was associated with a low to moderate FDG uptake, probably exerting its action through a metabolic shift of tracer influx to muscle and fat. Our results show that a single scan in the steady-state phase, e.g., 45-60 min from the injection, can be used for assessment of FDG uptake in tumors, making frequent blood sampling during imaging unnecessary. However, glucose concentration in blood must be monitored in patients with known or suspected abnormalities in glucose metabolism.