Liver Fat Quantification: Agreement and Reproducibility of Ultrasound-Derived Fat Fraction Measurements Using 5C1 and...

This study aimed to assess the agreement between the 5C1 and deep abdominal transducer (DAX) ultrasound probes when measuring ultrasound-derived fat fraction (UDFF) across different body mass index (BMI) categories and to evaluate the intra- and inter-observer reproducibility of liver fat measurements.In this prospective study 63 subjects (32 with BMI < 25 and 31 with BMI ≥ 25) underwent UDFF measurements. Two observers performed five measurements per subject using both probes (5C1 and DAX). Intra- and inter-observer reliability were assessed using intraclass correlation coefficients (ICC). Agreement between probes and observers was evaluated using Spearman correlation and Bland-Altman analysis, stratified by BMI subgroup.The intra- and inter-observer reliability of UDFF measurements were excellent, with no relevant systematic bias between observers or probes. The 5C1 and DAX probes showed strong correlations (r = 0.92 and 0.93). In normal-weight subjects, differences between probes were minimal, with limits of agreement (LoA) of approximately ±2%. In subjects with BMI ≥ 25, the mean differences between probes were low (up to 2.6%), but the limits of agreement were wider (-8% to +13%), comparable to the inter-observer variability.UDFF measurements with both the 5C1 and DAX probes showed consistently high reliability across BMI categories. Although variability increased with a higher BMI and liver fat, no systematic bias was observed, and both probes performed comparably. These findings support their interchangeable use in clinical settings. Validation against a reference standard is warranted to assess accuracy in challenging patient populations.