• Cheng William Hong, Tanya Wolfson, Ethan Z Sy, Alexandra N Schlein, Jonathan C Hooker, Soudabeh Fazeli Dehkordy, Gavin Hamilton, Scott B Reeder, Rohit Loomba, and Claude B Sirlin.
• Liver Imaging Group, Department of Radiology, University of California San Diego, San Diego, California, USA.
• J Magn Reson Imaging. 2018 Apr 1; 47 (4): 988-994.

BackgroundClinical 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.PurposeTo identify a strategy with the fewest ROIs that consistently achieves close agreement with the nine-ROI strategy.Study TypeRetrospective secondary analysis of prospectively acquired clinical research data.PopulationA total of 391 adults (173 men, 218 women) with known or suspected NAFLD.Field Strength/SequenceConfounder-corrected chemical-shift-encoded 3T MRI using a 2D multiecho gradient-recalled echo technique.AssessmentAn 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 TestingMean 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.ResultsThe 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) <1.5%, including four-ROI strategies with two ROIs from each lobe, which all had LOA <1.5%. 14/36 (39%) of two-ROI strategies and 74/84 (88%) of three-ROI strategies had ICC >0.995, and 2/36 (6%) of two-ROI strategies and 46/84 (55%) of three-ROI strategies had LOA <1.5%.Data ConclusionFour-ROI sampling strategies with two ROIs in the left and right lobes achieve close agreement with nine-ROI PDFF.Level Of Evidence3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:988-994.© 2017 International Society for Magnetic Resonance in Medicine.

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