Standardized Approach for ROI-Based Measurements of Proton Density Fat Fraction and R2* in the Liver

Abstract

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.

Diurnal Variation of Proton Density Fat Fraction in the Liver Using Quantitative Chemical Shift Encoded MRI

“…The largest elliptical ROI that would fit in each of the segments (with minimum area of 2 cm 2 ) was chosen while avoiding large vessels and bile ducts. This strategy has been demonstrated to reduce both intra‐ and interreader variability . The average of the nine liver ROI measurements was averaged together to provide a single MRI‐PDFF estimate for each CSE‐MRI acquisition.…”

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

“…Vu et al demonstrated that sampling strategies that sampled the right lobe exclusively estimated significantly different PDFF values compared to sampling strategies that sampled both lobes of the liver . Campo et al suggested that placing four ROIs (one in each of the anterior, posterior, medial, and lateral segments of the liver) may be a reasonable compromise between minimizing time burden and maximizing reader agreement . Our study adds to those studies by demonstrating that a simple sampling strategy of placing two ROIs in each lobe provides high accuracy for whole liver PDFF estimation using the nine‐ROI average as the reference standard.…”

“…Prior studies demonstrated that sampling strategies that included more segments, used larger ROIs, or sampled both lobes of the liver had significantly improved correlation with liver mean PDFF, and that the repeatability of liver PDFF measurements improves as the size and number of ROIs increase . Vu et al demonstrated that sampling strategies that sampled the right lobe exclusively estimated significantly different PDFF values compared to sampling strategies that sampled both lobes of the liver .…”

Validation of a motion‐robust 2D sequential technique for quantification of hepatic proton density fat fraction during free breathing

“…For phantoms, a single circular region of interest (ROI) (2 cm diameter) was positioned in a central slice of the phantom, sufficiently large to cover the majority of the cross‐section of each vial, while avoiding the edges and potential volume averaging artifacts. For the human study, we used a previously validated method, with ROIs placed by a trained analyst (Reader 1, B.D.P., abdominal imaging clinical fellow with 5 years of MRI interpretation experience) in each of the nine Couinaud segments of the liver in order to sample representative portions of the entire liver. The PDFF in each of the nine ROIs was averaged as a single composite hepatic PDFF value for every patient and acquisition.…”

“…As obesity rates in the United States rise, nonalcoholic fatty liver disease (NAFLD) is becoming increasingly prevalent in both adult and pediatric populations. At the cellular level, NAFLD results from intracellular deposition of triglycerides within hepatocytes, ie, hepatic steatosis.…”