Diagnostic Value and Influencing Factors of Ultrasound‐Derived Fat Fraction for Quantifying MASLD in Children

ABSTRACT Background & Aims To evaluate the diagnostic performance of ultrasound‐derived fat fraction (UDFF) for quantifying Metabolic dysfunction‐associated steatotic liver disease (MASLD) in children, using Magnetic resonance imaging‐derived proton density fat fraction (MRI‐PDFF) as the reference standard. Methods This prospective study enrolled 70 children with a median age of 12.23 years [IQR, 10.47–14.29] from December 2025 to April 2026. All participants underwent UDFF, MRI‐PDFF, and point shear wave elastography (pSWE) examinations. Steatosis was defined as MRI‐PDFF ≥ 6.4%. Correlations, agreement, diagnostic accuracy, and bias predictors were assessed using Pearson/Spearman correlation, Bland–Altman, ROC curves, and multivariable regression. Results Of 70 participants, 42 had MASLD. UDFF correlated strongly with MRI‐PDFF ( r = 0.84, p < 0.001). Overall mean bias was −2.19% (95% concordance limits: −15.07% to 10.68%), with a more pronounced systematic numerical bias observed in moderate‐to‐severe steatosis (mean bias −9.23%). No significant bias predictors were found. For detecting steatosis (≥ 6.4%), UDFF had an AUC of 0.98, optimal cutoff 5.5% (sensitivity 97.6%, specificity 92.9%, accuracy 95.7%); for ≥ S2 steatosis, the cutoff was 12.5% (AUC 0.96). Intraclass correlation for five repeated UDFF measurements was 0.98 (95% CI: 0.98–0.99). Visceral fat thickness ( β = 2.004, p = 0.003) and measurement depth ( β = 4.716, p = 0.033) independently predicted UDFF values. UDFF showed a weak negative correlation with pSWE Young's modulus ( r = −0.258, p = 0.033). Conclusions UDFF is a non‐invasive, accurate, and reproducible tool for quantifying paediatric hepatic steatosis. Although a systematic numerical bias exists relative to MRI‐PDFF in moderate‐to‐severe cases, UDFF retains excellent discriminative ability and is suitable for screening, staging, and longitudinal follow‐up of paediatric MASLD.