A PET/MRI study on the effect of obesity and NAFLD on hepatic [¹⁸F]FDG uptake

The potential limitations of hepatic [¹⁸F]FDG-PET imaging for individuals with obesity and excessive liver fat (NAFLD) are being investigated. In this study, we aim to determine the reliability of standardized uptake values (SUVs) focusing on adjustment for liver fat content (LFC) derived from DIXON images and the effects of whole-body normalizations.

Lean and with obesity volunteers who underwent [¹⁸F]FDG-PET/MRI were reviewed retrospectively. DIXON fat images were used to determine LFC and for adjustment of SUV_mean. The hepatic SUVs (mean, fat adjusted mean and max) were normalized to body weight, lean body mass and body surface area. Blood samples were analysed for glucose, serological liver enzymes and lipoproteins for further correlation of [¹⁸F]FDG uptake.

Out of 11 volunteers with obesity (M:8, F:3, BMI:30-39 kg/m²), 9 confirmed the presence of NAFLD (>5.6 % fat). 22 age-matched lean volunteers (M:10, F:11, BMI:19-26 kg/m²) were used as control group. Both SUV_mean, before and after adjustment to LFC, did not provide any difference between lean and with obesity groups under BW, LBM and BSA. SUV_max BW showed a difference between groups (p = 0.05). SUVs were independent of levels of GPT, GOT, gGT, insulin, HOMA-IR, triglycerides, cholesterol and LDL. Volunteers with low HDL were clustered with an increased hepatic [¹⁸F]FDG uptake.

Our method for adjustment of hepatic [¹⁸F]FDG-PET with DIXON fat images allows to achieve accurate results for individuals with NAFLD and obesity. For homogenic results, raw SUV_mean should be combined with adjustment for liver fat, appropriate normalization and consideration of HDL levels.