Heterogeneity of hepatic fat deposition in obese children based on mri-pdff and its correlation with clinical indicators

Objective To investigate the spatial heterogeneity of hepatic fat deposition in children with obesity using magnetic resonance imaging-proton density fat fraction (MRI-PDFF) and its association with clinical indicators, to clarify the dose-response relationship between liver enzyme levels and whole-liver PDFF, and to provide evidence for the precise assessment and intervention of pediatric nonalcoholic fatty liver disease (NAFLD). Methods A total of 113 consecutive obese children (84 males, 29 females) hospitalized in the Department of Endocrinology, Children’s Hospital, Zhejiang University School of Medicine, from January 2019 to December 2022 were enrolled. The median age was 11.00 years (IQR, 10.00–13.00 years). All subjects underwent liver MRI with the mDixon-Quant sequence. Regions of interest (ROIs) were placed in nine liver segments according to the Couinaud classification to measure and calculate PDFF for the whole liver, lobes, and segments. Repeated measures analysis of variance (ANOVA) was used to examine the differences in PDFF among the segments. Paired t-tests compared PDFF and internal variability between the left and right lobes. Linear mixed-effects models analyzed the independent associations between clinical indicators and segmental PDFF. Restricted cubic splines explored the dose-response relationship between clinical indicators and whole-liver PDFF. Results Among the 113 obese children, 91 (80.5%) had NAFLD. Repeated measures ANOVA showed significant PDFF differences among the nine segments (Greenhouse-Geisser corrected F=116.93, p<0.001). PDFF in the right lobe was significantly higher than in the left lobe (22.9% vs. 18.4%, difference=4.57%, 95%CI: 4.23%–4.91%, p<0.001). At the segmental level, segment VII had the highest PDFF, and segment I the lowest. The PDFF difference between the right and left lobes was significantly positively correlated with whole-liver PDFF (r=0.304, p=0.003). For each 1% increase in whole-liver PDFF, the difference increased by 0.096% (R 2 =0.093). Linear mixed-effects models revealed that alanine aminotransferase (ALT, estimate=0.066, p=0.002), total bile acids (TBA, estimate=1.47, p=0.006), and gamma-glutamyl transferase (GGT, estimate=0.11, p=0.042) were independently and positively associated with segmental PDFF. Restricted cubic spline analysis confirmed nonlinear associations of ALT and GGT with whole-liver PDFF (both p<0.001), with inflection points at 48.01 U/L and 44.21 U/L, respectively. The positive association strength was significantly higher before the inflection points compared to after. Conclusion Hepatic fat deposition in obese children exhibits significant spatial heterogeneity at the lobar and segmental levels, with the right lobe and segment VII being high-risk areas. ALT and GGT show a nonlinear dose-response relationship with whole-liver PDFF, with clear clinical intervention thresholds. These findings provide evidence for precise imaging assessment, non-invasive screening, and individualized intervention for pediatric NAFLD.