Comparison of ultrasound-derived fat fraction and hepatorenal index for quantitative detection of hepatic steatosis: a multicenter MRI-PDFF-referenced study.

BACKGROUND: MRI-PDFF enables accurate non-invasive quantification of liver fat, but its routine use is limited by cost, availability, and workflow constraints. Ultrasound-derived fat fraction (UDFF) may offer a more accessible quantitative alternative, yet its added value over the conventional hepatorenal index (HRI) remains uncertain when both are judged against the same MRI-PDFF reference standard. METHODS: This secondary cross-sectional analysis included 137 participants from a prospectively collected three-center cohort with MRI-PDFF, UDFF, and evaluable HRI measurements. Hepatic steatosis was defined as MRI-PDFF ≥5.0%. Diagnostic performance was compared using ROC analysis and paired DeLong testing, with center-stratified and alternative MRI-PDFF threshold analyses. Measurement reproducibility was evaluated for both UDFF and HRI. RESULTS: MRI-PDFF-defined hepatic steatosis was present in 85 of 137 participants. UDFF showed higher diagnostic discrimination than HRI (AUC, 0.945 [95% CI, 0.907-0.983] vs. 0.779 [95% CI, 0.700-0.859]; paired DeLong p = 0.0002), with consistently high center-specific AUCs (0.910-0.960) and similar results across MRI-PDFF thresholds of 5.2, 5.5, and 6.0%. UDFF demonstrated excellent within-examination repeatability and good interobserver reproducibility (ICC, 0.983 and 0.884, respectively); HRI also showed good intraobserver and interobserver reproducibility (ICC, 0.889 and 0.844, respectively). CONCLUSION: In this three-center cohort, UDFF provided stronger and more consistent MRI-PDFF-referenced discrimination for hepatic steatosis than HRI, while both methods showed good measurement reproducibility. UDFF may therefore provide a more robust quantitative ultrasound approach for hepatic steatosis assessment.