Abstract

SUV normalized by total body weight is affected by the amount of body fat. The SUV of normal tissues and lesions is higher (overestimated) in obese patients than in patients with a normal body mass index (BMI). SUL (SUV normalized by lean body mass [LBM]) is recommended for more accurate SUV results. Given the importance of a quantitative PET parameter, particularly when comparing PET studies, we aimed to revisit the effect of obesity on SUV, measuring SUL in normal-BMI patients and obese patients and testing the effect of the amount of LBM. Methods: 18F-FDG whole-body images of adult patients were analyzed retrospectively. We measured both SUVmax and SUVmean in the blood pool and liver of patients with a normal BMI (18.5-24.9) and a high BMI (≥30) (obese). In all patients, we calculated LBM via an equation using patient height and weight and corrected all SUVs to SULs. Mean (±SD) SUVs and SULs were compared under various circumstances. Scatterplots were generated for weight and SUV-SUL differences. Results: SUVmean in the liver and blood pool was significantly higher in obese patients (30 patients) than in patients with a normal BMI (20 patients) (4.1 ± 0.7 and 3.0 ± 0.5, respectively, in liver, vs. 3.2 ± 0.6 and 2.4 ± 0.4, respectively, in blood pool; P < 0.001). SULmean was significantly lower in both liver and blood pool in all patients, being approximately 75% of SUVmean in patients with a normal BMI and 55% of SUVmean in obese patients (P < 0.001). SULmean in the liver and blood pool did not significantly differ between obese patients and normal-BMI patients (P > 0.05). The SUV-SUL difference was significantly higher in obese patients than in patients with a normal BMI (P < 0.001). These statistical results were the same when SUVmax and SULmax were compared. Conclusion: SUV overestimates metabolic activity in all patients, and this overestimation is more significant in obese patients than in patients with a normal BMI. SUL is not affected by body weight or the amount of LBM.

Keywords: PET; SUL; SUV; lean body mass; weight.