Quantifying Abdominal Adipose Tissue and Thigh Muscle Volume and Hepatic Proton Density Fat Fraction: Repeatability and Accuracy of an MR Imaging-based, Semiautomated Analysis Method

Abstract

Purpose To determine the repeatability and accuracy of a commercially available magnetic resonance (MR) imaging-based, semiautomated method to quantify abdominal adipose tissue and thigh muscle volume and hepatic proton density fat fraction (PDFF). Materials and Methods This prospective study was institutional review board- approved and HIPAA compliant. All subjects provided written informed consent. Inclusion criteria were age of 18 years or older and willingness to participate. The exclusion criterion was contraindication to MR imaging. Three-dimensional T1-weighted dual-echo body-coil images were acquired three times. Source images were reconstructed to generate water and calibrated fat images. Abdominal adipose tissue and thigh muscle were segmented, and their volumes were estimated by using a semiautomated method and, as a reference standard, a manual method. Hepatic PDFF was estimated by using a confounder-corrected chemical shift-encoded MR imaging method with hybrid complex-magnitude reconstruction and, as a reference standard, MR spectroscopy. Tissue volume and hepatic PDFF intra- and interexamination repeatability were assessed by using intraclass correlation and coefficient of variation analysis. Tissue volume and hepatic PDFF accuracy were assessed by means of linear regression with the respective reference standards. Results Adipose and thigh muscle tissue volumes of 20 subjects (18 women; age range, 25-76 years; body mass index range, 19.3-43.9 kg/m2) were estimated by using the semiautomated method. Intra- and interexamination intraclass correlation coefficients were 0.996-0.998 and coefficients of variation were 1.5%-3.6%. For hepatic MR imaging PDFF, intra- and interexamination intraclass correlation coefficients were greater than or equal to 0.994 and coefficients of variation were less than or equal to 7.3%. In the regression analyses of manual versus semiautomated volume and spectroscopy versus MR imaging, PDFF slopes and intercepts were close to the identity line, and correlations of determination at multivariate analysis (R2) ranged from 0.744 to 0.994. Conclusion This MR imaging-based, semiautomated method provides high repeatability and accuracy for estimating abdominal adipose tissue and thigh muscle volumes and hepatic PDFF. © RSNA, 2017.

Figures

Figure 1:

Schematic shows workflow for MR imaging examinations. MRS = MR spectroscopy.

Figure 2:

Coronal, sagittal, and axial reconstructions of segmented image stacks for each acquisition (baseline and repeats 1 and 2). SCAT (blue) volume was measured superiorly from T9 to top of the femoral head by using the semiautomated method. VAT (green) and thigh muscle volumes were measured in their entirety. Left anterior, left posterior, right anterior, and right posterior muscle groups are color coded for clarity.

Figure 3:

Axial MR images show manual segmentation, A, abdominal SCAT (pink) and VAT (purple); and, B, thigh muscle (red).

Figure 4:

Bland-Altman plots for intraexamination (blue circle) and interexamination (red triangle) repeatability of semiautomated analysis method–determined volume estimates, respectively, for, A, abdominal SCAT; B, abdominal VAT; C, TAT; and, D, thigh muscle volume ( TMV ). Intraexamination repeatability was evaluated by comparing baseline and repeat 1. Interexamination repeatability was evaluated by comparing baseline and repeat 3. Dashed gray line for each case represents zero bias. Central solid line is at bias level for each case, and upper and lower lines are 95% limits of agreement. Note that, for each compartment, intra- and interexamination results are similar. Bland-Altman metrics are summarized in Table 3.

Figure 5:

Regression plots of manually determined versus semiautomated tissue volumes for, A, SCAT; B, VAT; C, TAT; and D, thigh muscle volume ( TMV ). Semiautomated estimates (predictors) are plotted on x-axes. Manually determined measurements (reference standards) are plotted on y-axes. Red line in each plot is identity line.

Figure 6:

A, Bland-Altman plot for intraexamination (blue circles) and interexamination (red triangles) repeatability of semiautomated analysis method–estimated hepatic PDFF and, B, regression plot of MR spectroscopy versus semiautomated hepatic PDFF. Semiautomated PDFF (the predictor) is plotted on x-axis. MR spectroscopic PDFF (reference standard) is plotted on y-axis. Red line is identity line. Bland-Altman metrics are summarized in Table 3.