Interexamination repeatability and spatial heterogeneity of liver iron and fat quantification using MRI-based multistep adaptive fitting algorithm.

PURPOSE: To assess the interexamination repeatability and spatial heterogeneity of liver iron and fat measurements using a magnetic resonance imaging (MRI)-based multistep adaptive fitting algorithm.
MATERIALS AND METHODS: This prospective observational study was Institutional Review Board-approved and Health Insurance Portability and Accountability Act-compliant. Written informed consent was waived. In all, 150 subjects were imaged on 3T MRI systems. A whole-liver volume acquisition was performed twice using a six-echo 3D spoiled gradient echo sequence during two immediately adjacent examinations. Colocalized regions of interest (ROIs) in three different hepatic segments were placed for R2 * and proton density fat fraction (PDFF) measurements by two readers independently. Mean R2 * and PDFF values between readers and acquisitions were compared using the Wilcoxon signed-rank test, intraclass correlation coefficients (ICCs), linear regression, Bland-Altman analysis, and analysis of variance (ANOVA).
RESULTS: The mean R2 * and PDFF values across all ROIs and measurements were 51.2 ± 25.2 s(-1) and 6.9 ± 6.4%, respectively. Mean R2 * and PDFF values showed no significant differences between the two acquisitions (P = 0.05-0.87). Between the two acquisitions, R2 * and PDFF values demonstrated almost perfect agreement (ICCs = 0.979-0.994) and excellent correlation (R(2)  = 0.958-0.989). Bland-Altman analysis also demonstrated excellent agreement. In the ANOVA, the individual patient and ROI location were significant effects for both R2 * and PDFF values (P < 0.05).
CONCLUSION: MRI-based R2 * and PDFF measurements are repeatable between examinations. Between-measurement changes in R2 * of more than 10.1 s(-1) and in PDFF of more than 1.7% are likely due to actual tissue changes. Liver iron and fat content are variable between hepatic segments.