OBJECTIVE The purpose of this study was to evaluate the reproducibility (interreviewer agreement) and repeatability (intrareviewer agreement) of ROI sampling strategies to measure chemical shift–encoded (CSE) MRI-based liver proton density fat fraction (PDFF) and R2* (1 / T2*). A secondary purpose was to standardize ROI-based liver PDFF and R2* measurements by providing a compromise between measurement reproducibility and repeatability and time burden for image analysts. MATERIALS AND METHODS CSE data from two cohorts were retrospectively analyzed. Cohort A included 53 patients referred for abdominal MRI and healthy subjects recruited for a comparison study of CT and MRI. Cohort B included 37 patients with suspected liver iron overload. Three reviewers measured liver PDFF and R2* using previously reported ROI sampling strategies. Inter- and intrareviewer agreement of liver PDFF and R2* were evaluated using Bland-Altman analysis. RESULTS Averaging largest-fit ROIs over the nine Couinaud segments resulted in the narrowest limits of agreement (LOA) for liver PDFF and R2* measurements in both cohorts. For PDFF, interreviewer agreement had mean LOA of ± 0.8% for cohort A and ± 1.7% for cohort B. Intrareviewer agreement was ± 0.5% for cohort A and ± 0.9% for cohort B. For R2* interreviewer agreement had mean LOA of ± 3.0 s−1 for cohort A and ± 17.9 s−1 for cohort B. Intrareviewer agreement was ± 2.6 s−1 for cohort A and ± 14.6 s−1 for cohort B. This approach was the most time-burdensome, requiring a mean ± SD of 149.7 ± 8.6 s per dataset. CONCLUSION For improved reproducibility and repeatability of liver PDFF and R2* measurements, clinicians and researchers should sample as much area of the liver as possible using multiple large ROIs.

Background Whole‐organ, noninvasive techniques for the detection and quantification of nonalcoholic fatty liver disease features have clinical and research applications. However, the effect of time of day, hydration status, and meals are unknown factors with potential to impact bias, precision, reproducibility, and repeatability of chemical shift‐encoded MRI (CSE‐MRI) to quantify liver proton density fat fraction (PDFF). Purpose To assess the effect of diurnal variation on PDFF using CSE‐MRI, including the effect of time of day, the effect of meals and hydration status, as well as the day to day variability. Study Type Prospective. Subjects Eleven healthy subjects and nine patients with observed hepatic steatosis. Field Strength/Sequences A commercial quantitative confounder‐corrected CSE‐MRI sequence (IDEAL IQ) and an MR spectroscopy (MRS) sequence (multiecho STEAM) were acquired at 1.5T. Assessment MRI‐PDFF and MRS‐PDFF estimates were compared across six visits (before and after a controlled breakfast, before and after an uncontrolled lunch, at approximately 4 pm, and then before breakfast on the following day) with three repeated measures for a total of 360 MRI‐PDFF and MRS‐PDFF measurements. Statistical Tests Linear regression, Bland–Altman analysis, and mixed effect models were used to determine the bias, precision, and repeatability of PDFF measurements. Results No statistically significant linear trend was observed across visits for either MRI‐PDFF or MRS‐PDFF (P = 0.31 and 0.37, respectively). The repeatability was measured to be 0.86% for MRI‐PDFF and 1.1% for MRS‐PDFF over all six visits. For MRI‐PDFF, the variability between all six visits (0.94%) was only slightly higher than within each visit (0.66%), with P < 0.001. For MRS‐PDFF, the variability between all six visits was 1.29%, compared with 0.87% within each visit (P < 0.001). Data Conclusion Our results may indicate that it is not necessary to control for the time of day or the fasting/fed state of the patient when measuring PDFF using CSE‐MRI. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:407–414.