The influence of adipose tissue volume can significantly affect the metabolic activity of reference organs in 18F-FDG PET/CT studies of a normal healthy population.

OBJECTIVE: This study investigated whether fluorine-18-fluorodeoxyglucose (18F-FDG) uptake of reference organs can be affected by subjects' factors in positron emission tomography/computed tomography (PET/CT) in a healthy population. SUBJECTS AND METHODS: A total of 208 normal healthy subjects without diabetes or dyslipidemia were included. Adipose tissue volume was measured by CT images from a dedicated PET/CT scan. Uptake of 18F-FDG of reference organs was measured from liver, blood pool, and muscle, and was normalized by lean body anthropometric data and adipose tissue volume. RESULTS: Of 208 participants, 118 were metabolically healthy lean (MHL); with body mass index (BMI) <25kg/m2 and 90 were metabolically healthy obese (MHO) with; BMI≥25kg/m2 . These subjects had significantly higher values of liver, blood pool, and muscle than did the MHL subjects (P<0.001 for both). Among subjects' factors, adipose tissue volume revealed strongest correlation with standardized uptake value multiplied by lean body weight divided by body weight (SUL) of liver (r=0.754, P<0.001), of blood pool (r=0.756, P<0.001) and of muscle (r=0.635, P<0.001). On regression analysis, adipose tissue volume was determined to be a common independent predictor for SUL of liver, blood pool and muscle (P<0.001) and furthermore was serum C-reactive protein level for SUL of the liver and also age and serum insulin level for SUL of blood pool. CONCLUSION: Adipose tissue volume can significantly affect SUL of liver, blood pool, and muscle in a healthy population. Liver and blood pool may have limited roles as reference organs for normalization of 18F-FDG uptake of the lesion.