The effect of blood glucose level on normal FDG distribution to the cerebellum, the liver, and skeleton muscles

Objectives In oncological FDG PET or PET/CT studies, FDG activities in the cerebellum, liver or skeleton muscles (so-called reference organs) are often used for the calculation of a lesion-to-reference organ ratio in an effort to improve diagnostic accuracy. This project was designed to test our hypothesis that blood glucose levels would have various, but significant effects on FDG activities in the reference organs.

Methods A total of 61 patients’ charts were retrospectively reviewed with institutional approval. The patients were grouped into hypoglycemic (n=25; 50.5±5.2 mg/dL), normoglycemic (n=22; 89.2±12.4 mg/dL), and hyperglycemic (n=14; 251±41 mg/dL) subjects. Maximum SUVs of the three reference organs (e.g., the cerebellum, the liver dome, and the right gluteal muscles) were measured by two nuclear medicine physicians. Unpaired student T-tests were performed, and p<0.05 was considered as statistically significant.

Results In the cerebellum, FDG activity is overall inversely correlated with the blood glucose levels, which is compatible with competitive inhibition. By contrast, FDG activity in the liver slightly increases with rising blood glucose levels, suggesting a minimally enhanced, glucose-dependent metabolism, although there are marginal difference between the three groups. FDG activities in the gluteal muscles are the lowest among the three organs, and overall there is no statistical significance among the patients with hypoglycemia, normoglycemia, or hyperglycemia. However, there is a large variation of FDG activity among the hypoglycemic patients, with SUVs ranging from 0.3 to 4.1, which is probably due to a wide range of endogeneous insulin levels.

Conclusions Data presented here suggest that the liver is an organ with relatively stable FDG activity, nearly independent from blood glucose levels. If the cerebellum deems to be a reference organ, data with blood glucose correction is warranted