MRI Proton Density Fat Fraction From PET/MRI Elucidates the Biphasic Impact of Hepatic Steatosis on Liver 18F-FDG Uptake

Objective: The effect of hepatic steatosis on liver 18 F-FDG uptake remains unclear, as previous PET/CT-based studies have reported inconsistent findings. This study aimed to investigate the impact of hepatic steatosis on 18 F-FDG uptake and to identify the factors influencing the liver standardized uptake value (SUV) using PET/MRI. Methods: A total of 188 participants who underwent PET/MRI for cancer screening between January 2017 and December 2021 were evaluated. The liver fat fraction was quantified using MRI proton density fat fraction (PDFF). Participants were classified into 3 groups based on PDFF thresholds: normal (<6%), mild steatosis (6% to 17%), and moderate-to-severe steatosis (>17%). Liver SUV max and SUV mean were measured and analyzed for correlations with age, body mass index (BMI), serum lipids, PDFF, and iron deposition. Multivariate and segmented regression analyses were performed to identify independent predictors of liver SUV. Results: Liver SUV max and SUV mean increased with mild steatosis but decreased with moderate-to-severe steatosis ( P <0.001). Triglyceride (β=0.068, P =0.002), high-density lipoprotein cholesterol (β=−0.295, P =0.001), body mass index (β=0.018, P =0 .037), and age (β=0.007, P =0.007) independently predicted liver SUV mean . PDFF was positively associated with SUV mean in normal livers but negatively associated with fatty livers. Conclusions: PET/MRI demonstrated that hepatic steatosis, as assessed by PDFF, significantly influenced liver 18 F-FDG uptake in a biphasic manner. These findings underscore the importance of integrating fat quantification into PET interpretation to improve the accuracy of oncologic imaging.