Abstract
241666
Introduction: Previous studies have found that liver steatosis, body mass index (BMI), and blood glucose levels may influence hepatic fluorodeoxyglucose (FDG) uptake, commonly used as a reference tissue in semi-quantitative assessments. However, these findings have been inconsistent and somewhat controversial [1-4]. For instance, Abikhzer et al. noted that fatty deposits in the liver reduce liver metabolic activity [4], while Pak et al. found a positive correlation between liver FDG uptake and BMI, but not with the degree of liver steatosis [3]. Furthermore, Kermida et al. reported a positive correlation between liver SUVmax and blood glucose, with a negative correlation to liver CT value, while liver SUVmean was positively correlated with CT value [2]. Understanding liver FDG uptake is crucial in clinical settings, especially when using the liver as a reference tissue. This study aims to investigate the combined effects of hepatic fat (as evaluated with PET/MRI), BMI, and serum biochemical indexes on liver FDG uptake.
Methods: In this retrospective study, we reviewed PET/MRI scans (Biograph mMR, Siemens Healthcare, Erlangen, Germany) of 24,327 individuals. Out of these, 188 patients with complete laboratory examinations and imaging data were selected. The maximum and mean standardized uptake value (SUVmax and SUVmean) was used to quantify liver FDG uptake. The proton density fat fraction (PDFF) indicated the severity of liver fat, while PDFF and R2 water values were derived from a single-voxel MR spectroscopy sequence (HISTO, the LiverLab package, Siemens Healthcare). Height, weight, and blood biochemical tests (serum glucose, lipids, liver function, and C-reactive protein (CRP) levels) were also recorded. One-way ANOVA with least significant difference (LSD) analysis explored intergroup SUV differences across liver-fat-severity groups. Multivariate regression models identified variables that predicted the liver SUVmax before and after dichotomizing participants into low and high PDFF groups.
Results: The study population was categorized into groups with normal liver, mild liver fat infiltration, and moderate-severe liver fat, with PDFF cutoffs of 6% and 17% [5]. Participants with mild fatty liver exhibited higher SUVs than those in the normal liver group, with statistically significant differences noted both for SUVmax (P = 0.003) and SUVmean (P = 0.006). In contrast, the group with moderate-severe fatty liver showed lower SUVs compared to the mild fatty liver group, with this difference also being significant (P = 0.047 for SUVmax; P = 0.008 for SUVmean). An increasing trend in liver SUV was noted when moving from the normal group to the mild fat infiltration group. Conversely, a decreasing trend in liver SUV was observed from the mild to moderate-severe liver fat infiltration group (Figure 1).
We further created linear regression models with the adjustment of PDFF in two strata (low and high PDFF groups divided by a cutoff point of 6%). Different parameters showed associations in different groups (Figure 2).
Conclusions: PDFF, BMI, blood glucose, and triglyceride were essential variables predicting liver FDG uptake. Mild degree of fatty liver had a positive effect on liver 18F-FDG uptake, whereas a moderate to severe degree of fatty liver negatively affected 18F-FDG uptake. Attention should be paid to liver metabolism in patients with fatty liver before using the liver as a reference tissue in determining focal FDG uptake elsewhere within the abdomen.
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