Optimization of region‐of‐interest sampling strategies for hepatic MRI proton density fat fraction quantification

BACKGROUND Clinical trials utilizing proton density fat fraction (PDFF) as an imaging biomarker for hepatic steatosis have used a laborious region‐of‐interest (ROI) sampling strategy of placing an ROI in each hepatic segment. PURPOSE To identify a strategy with the fewest ROIs that consistently achieves close agreement with the nine‐ROI strategy. STUDY TYPE Retrospective secondary analysis of prospectively acquired clinical research data. POPULATION A total of 391 adults (173 men, 218 women) with known or suspected NAFLD. FIELD STRENGTH/SEQUENCE Confounder‐corrected chemical‐shift‐encoded 3T MRI using a 2D multiecho gradient‐recalled echo technique. ASSESSMENT An ROI was placed in each hepatic segment. Mean nine‐ROI PDFF and segmental PDFF standard deviation were computed. Segmental and lobar PDFF were compared. PDFF was estimated using every combinatorial subset of ROIs and compared to the nine‐ROI average. STATISTICAL TESTING Mean nine‐ROI PDFF and segmental PDFF standard deviation were summarized descriptively. Segmental PDFF was compared using a one‐way analysis of variance, and lobar PDFF was compared using a paired t‐test and a Bland–Altman analysis. The PDFF estimated by every subset of ROIs was informally compared to the nine‐ROI average using median intraclass correlation coefficients (ICCs) and Bland–Altman analyses. RESULTS The study population's mean whole‐liver PDFF was 10.1 ± 8.9% (range: 1.1–44.1%). Although there was no significant difference in average segmental (P = 0.452) or lobar (P = 0.154) PDFF, left and right lobe PDFF differed by at least 1.5 percentage points in 25.1% (98/391) of patients. Any strategy with ≥4 ROIs had ICC >0.995. 115 of 126 four‐ROI strategies (91%) had limits of agreement (LOA)