WFUMB-Recommended Versus Manufacturer-Optimized Protocols for Ultrasound-Guided Attenuation Parameter in Hepatic Steatosis Assessment: A Retrospective Single-Vendor Multicenter Study

Background/Objectives: The ultrasound-guided attenuation parameter (UGAP) is conventionally measured at a 4 cm start depth from the skin with a 4 cm region of interest (ROI), whereas 2024 World Federation for Ultrasound in Medicine and Biology (WFUMB) guidance recommends 2 cm from the liver capsule with a 3 cm ROI. We compared these two ROI configurations, applied to the same archived acquisitions, against MRI-derived proton density fat fraction (MRI-PDFF). Methods: This retrospective study included 565 patients with chronic liver disease from four of six participating Japanese centers at which raw data had been stored. Conventional UGAP was measured in real time; WFUMB-based values were calculated retrospectively from the same acquisitions, without real-time operator optimization. Performance was assessed by receiver operating characteristic analysis and the Obuchowski index, with integrated discrimination improvement (IDI) and net reclassification improvement (NRI) as secondary analyses. Results: Areas under the curve did not differ significantly at any threshold (≥S1: 0.92 [95% CI: 0.90–0.94] vs. 0.92 [0.89–0.94]; p = 0.07–0.23). Conventional UGAP correlated slightly more strongly with MRI-PDFF (ρ = 0.83 vs. 0.81; Δρ = 0.02; p < 0.01) and had a higher Obuchowski index (0.92 vs. 0.91; p = 0.04); both differences were statistically significant but of doubtful clinical relevance, and secondary IDI/NRI analyses were directionally consistent but imprecise. Body mass index was the strongest independent predictor of the inter-protocol difference. Conclusions: Neither ROI configuration showed a clinically meaningful advantage on this single-vendor platform. Small differences favoring the manufacturer-optimized configuration were not uniform across centers and may largely reflect acquisition asymmetry. No equivalence margin was prespecified, so these data show no demonstrable advantage for either configuration rather than establishing equivalence and require confirmation in a prospective paired study.