Accuracy of multiecho magnitude-based MRI (M-MRI) for estimation of hepatic proton density fat fraction (PDFF) in children

Abstract

Purpose: To assess accuracy of magnitude-based magnetic resonance imaging (M-MRI) in children to estimate hepatic proton density fat fraction (PDFF) using two to six echoes, with magnetic resonance spectroscopy (MRS) -measured PDFF as a reference standard.

Methods: This was an IRB-approved, HIPAA-compliant, single-center, cross-sectional, retrospective analysis of data collected prospectively between 2008 and 2013 in children with known or suspected nonalcoholic fatty liver disease (NAFLD). Two hundred eighty-six children (8-20 [mean 14.2 ± 2.5] years; 182 boys) underwent same-day MRS and M-MRI. Unenhanced two-dimensional axial spoiled gradient-recalled-echo images at six echo times were obtained at 3T after a single low-flip-angle (10°) excitation with ≥ 120-ms recovery time. Hepatic PDFF was estimated using the first two, three, four, five, and all six echoes. For each number of echoes, accuracy of M-MRI to estimate PDFF was assessed by linear regression with MRS-PDFF as reference standard. Accuracy metrics were regression intercept, slope, average bias, and R(2) .

Results: MRS-PDFF ranged from 0.2-40.4% (mean 13.1 ± 9.8%). Using three to six echoes, regression intercept, slope, and average bias were 0.46-0.96%, 0.99-1.01, and 0.57-0.89%, respectively. Using two echoes, these values were 2.98%, 0.97, and 2.72%, respectively. R(2) ranged 0.98-0.99 for all methods.

Conclusion: Using three to six echoes, M-MRI has high accuracy for hepatic PDFF estimation in children.

Keywords: MRI; MRS; NAFLD; PDFF; liver steatosis; proton density fat fraction.

Figure 1

Representative images from three children with MRS-PDFF values of < 10%, 10 – 20%, and > 20% to illustrate agreement of M-MRI-PDFF and MRS-PDFF at the MRS voxel location. Two-, three-, and six-echo M-MRI-PDFF parametric maps were generated from source images by applying the algorithm pixel by pixel. For each case and echo number, M-MRI-PDFF measured in a region of interest (circle) corresponding to the MRS voxel is indicated.

Figure 2

Scatterplots for MRS-PDFF versus M-MRI-PDFF over a range of numbers of echoes from two to six. For each M-MRI method, regression intercept, regression slope, average bias, and R² are indicated.

Figure 3

Bland-Altman plots for MRS-PDFF and M-MRI-PDFF over a range of numbers of echoes from two to six.

Figure 4

Correlation analyses between histology steatosis grade and hepatic PDFF in 10 children with available liver biopsy results. The correlation coefficient was similar between histology steatosis grade and hepatic PDFF estimated by two- to six-echo M-MRI methods or MRS (Spearman’s rho = 0.71, p = 0.0213). MRS: MR Spectroscopy.