Nonalcoholic fatty liver disease: MR imaging of liver proton density fat fraction to assess hepatic steatosis

Abstract

Purpose: To evaluate the diagnostic performance of magnetic resonance (MR) imaging-estimated proton density fat fraction (PDFF) for assessing hepatic steatosis in nonalcoholic fatty liver disease (NAFLD) by using centrally scored histopathologic validation as the reference standard.

Materials and methods: This prospectively designed, cross-sectional, internal review board-approved, HIPAA-compliant study was conducted in 77 patients who had NAFLD and liver biopsy. MR imaging-PDFF was estimated from magnitude-based low flip angle multiecho gradient-recalled echo images after T2* correction and multifrequency fat modeling. Histopathologic scoring was obtained by consensus of the Nonalcoholic Steatohepatitis (NASH) Clinical Research Network Pathology Committee. Spearman correlation, additivity and variance stabilization for regression for exploring the effect of a number of potential confounders, and receiver operating characteristic analyses were performed.

Results: Liver MR imaging-PDFF was systematically higher, with higher histologic steatosis grade (P < .001), and was significantly correlated with histologic steatosis grade (ρ = 0.69, P < .001). The correlation was not confounded by age, sex, lobular inflammation, hepatocellular ballooning, NASH diagnosis, fibrosis, or magnetic field strength (P = .65). Area under the receiver operating characteristic curves was 0.989 (95% confidence interval: 0.968, 1.000) for distinguishing patients with steatosis grade 0 (n = 5) from those with grade 1 or higher (n = 72), 0.825 (95% confidence interval: 0.734, 0.915) to distinguish those with grade 1 or lower (n = 31) from those with grade 2 or higher (n = 46), and 0.893 (95% confidence interval: 0.809, 0.977) to distinguish those with grade 2 or lower (n = 58) from those with grade 3 (n = 19).

Conclusion: MR imaging-PDFF showed promise for assessment of hepatic steatosis grade in patients with NAFLD. For validation, further studies with larger sample sizes are needed.

Figure 1:

Flowchart of patient selection.

Figure 2:

NAFLD in a 8-year-old girl with grade-3 steatosis determined by histologic validation. Average PDFF across the nine segments in this patient was 39%. A–F, Multiecho MR imaging with TEs of 2.3, 4.6, 6.9, 9.2, 11.5, and 13.8 msec, respectively. G, Plot of signal intensity (in arbitrary units) in a representative pixel acquired over the range 2.3–13.8 msec. H, Estimated grayscale MR imaging–PDFF map with the multiecho multi-interference image analysis technique. PDFF for the individual pixel at the tip of the arrows was estimated to be 38%, and T2* was estimated to be 25 msec.

Figure 3:

Box and whisker plot shows MR imaging–estimated PDFF is higher with progressively larger steatosis grade. The percentage range of hepatocytes with macrovesicular steatosis is shown in parentheses along the x-axis. MRI = MR imaging.

Figure 4:

Receiver operating characteristic curve analysis of MR imaging–PDFF for classification of dichotomized steatosis grades determined by histologic validation: 0 versus ≥1 (area under the curve = 0.989), ≤1 versus ≥2 (area under the curve = 0.825), and ≤2 versus 3 (area under the curve = 0.893).