Purpose

MRI proton density fat fraction (PDFF) can be calculated using magnitude (MRI-M) or complex (MRI-C) MRI data. The purpose of this study was to identify, assess, and compare the accuracy of common PDFF thresholds for MRI-M and MRI-C for assessing hepatic steatosis in patients with obesity, using histology as reference.

Methods

This two-center prospective study included patients undergoing MRI-C- and MRI-M-PDFF estimations within 3 days before weight loss surgery. Liver biopsy was performed, and histology-determined steatosis grades were used as reference standard. Using receiver operating characteristics (ROC) analysis on data pooled from both methods, single common thresholds for diagnosing and differentiating none or mild (0-1) from moderate to severe steatosis (2-3) were selected as the ones achieving the highest sensitivity while providing at least 90% specificity. Selection methods were cross-validated. Performances were compared using McNemar's tests.

Results

Of 81 included patients, 54 (67%) had steatosis. The common PDFF threshold for diagnosing steatosis was 5.4%, which provided a cross-validated 0.88 (95% CI 0.77-0.95) sensitivity and 0.92 (0.75-0.99) specificity for MRI-M and 0.87 sensitivity (0.75-0.94) with 0.81 (0.61-0.93) specificity for MRI-C. The common PDFF threshold to differentiate steatosis grades 0-1 from 2 to 3 was 14.7%, which provided cross-validated 0.86 (95% CI 0.59-0.98) sensitivity and 0.95 (0.87-0.99) specificity for MRI-M and 0.93 sensitivity (0.68-0.99) with 0.97(0.89-0.99) specificity for MRI-C.

Conclusion

If independently validated, diagnostic thresholds of 5.4% and 14.7% could be adopted for both techniques for detecting and differentiating none to mild from moderate to severe steatosis, respectively, with high diagnostic accuracy.

To assess and compare the diagnostic performance of magnitude-reconstruction chemical-shift-encoded magnetic resonance imaging (MRI-M) and complex-reconstruction chemical-shift-encoded magnetic resonance imaging (MRI-C) for diagnosis of hepatic steatosis in subjects with severe obesity without known non-alcoholic fatty liver disease (NAFLD), using contemporaneous histology as reference. This is an IRB-approved, HIPAA-compliant, two-center, cross-sectional study of a larger prospective trail that recruited patients without known NAFLD consecutively between October 2010 and March 2015 to undergo research MRI exams 1-2 days prior to clinical-care weight-loss surgery. Proton denisty fat fraction (PDFF) was estimated using MRI-M and MRI-C. Liver biopsies were obtained intraoperatively. Using histologically-determined presence of steatosis as the reference standard, receiver operating characteristics (ROC) analyses were used to identify MRI-M- and MRI-C-derived PDFF thresholds for diagnosing steatosis. Bootstrapped-based tests were used to compare their diagnostic performace. A total of 81 patients (67 female, 14 maile, average age 48.2) were recruited for this study. MRI-M and MRI-C had areas under the ROC curve of 0.951 and 0.947, respectively, for diagnosing hepatic steatosis. for MRI-M, the Youden-index-based PDFF threshold of 6.5% provided 0.87 sensitivity (95% confidence internal: 0/75, 0.95), 0.96 specificity (0.81, 0.99), and 0.90 total accuracy (0.82, 0.96). For MRI-C, a PDFF threshold of 6.8%, provided a 0.90 sensitivity (0.77, 0.96), 0.96 specificity (0.81, 0.99), and 0.91 total accuracy (0.83, 0.97). Differences in performance parameters between MRI-M and MRI-C were not statistically significant. Conclusion: MRI-M- and MRI-C-derived PDFF is accurate for non-invasive diagnosis of hepatic steatosis in subjects with severe obesity.