Intra- and inter-examination repeatability of magnetic resonance spectroscopy, magnitude-based MRI, and complex-based MRI for estimation of hepatic proton density fat fraction in overweight and obese children and adults

Abstract

Purpose: Determine intra- and inter-examination repeatability of magnitude-based magnetic resonance imaging (MRI-M), complex-based magnetic resonance imaging (MRI-C), and magnetic resonance spectroscopy (MRS) at 3T for estimating hepatic proton density fat fraction (PDFF), and using MRS as a reference, confirm MRI-M and MRI-C accuracy.

Methods: Twenty-nine overweight and obese pediatric (n = 20) and adult (n = 9) subjects (23 male, 6 female) underwent three same-day 3T MR examinations. In each examination MRI-M, MRI-C, and single-voxel MRS were acquired three times. For each MRI acquisition, hepatic PDFF was estimated at the MRS voxel location. Intra- and inter-examination repeatability were assessed by computing standard deviations (SDs) and intra-class correlation coefficients (ICCs). Aggregate SD was computed for each method as the square root of the average of first repeat variances. MRI-M and MRI-C PDFF estimation accuracy was assessed using linear regression with MRS as a reference.

Results: For MRI-M, MRI-C, and MRS acquisitions, respectively, mean intra-examination SDs were 0.25%, 0.42%, and 0.49%; mean intra-examination ICCs were 0.999, 0.997, and 0.995; mean inter-examination SDs were 0.42%, 0.45%, and 0.46%; and inter-examination ICCs were 0.995, 0.992, and 0.990. Aggregate SD for each method was <0.9%. Using MRS as a reference, regression slope, intercept, average bias, and R (2), respectively, for MRI-M were 0.99%, 1.73%, 1.61%, and 0.986, and for MRI-C were 0.96%, 0.43%, 0.40%, and 0.991.

Conclusion: MRI-M, MRI-C, and MRS showed high intra- and inter-examination hepatic PDFF estimation repeatability in overweight and obese subjects. Longitudinal hepatic PDFF change >1.8% (twice the maximum aggregate SD) may represent real change rather than measurement imprecision. Further research is needed to assess whether examinations performed on different days or with different MR technologists affect repeatability of MRS voxel placement and MRS-based PDFF measurements.

Keywords: Complex-based MRI; Hepatic steatosis; Inter-examination repeatability; Intra-examination repeatability; Magnetic resonance spectroscopy; Magnitude-based MRI; Obesity; PDFF; Proton density fat fraction; Quantitative imaging biomarkers.

Figures

Fig. 1

Intra-examination repeatability in a 14-year-old boy. Shown are three repeated magnetic resonance spectroscopy (MRS), magnitude-based magnetic resonance imaging (MRI-M), and complex-based magnetic resonance imaging (MRI-C) acquisitions within a single examination. The anatomic T2W single-shot fast spin echo image used to guide MRS voxel placement is shown. MRS voxel and MRI region of interest locations are overlain as well as the corresponding PDFF values. Notice close agreement between all methods and acquisitions (collages for Figs. 1 and 2 were created using Osirix 5.8 and Photoshop CS6).

Fig. 2

Inter-examination repeatability in a 14-year-old boy. Shown are first acquisitions of magnetic resonance spectroscopy (MRS), magnitude-based magnetic resonance imaging (MRI-M), and complex-based magnetic resonance imaging (MRI-C) for each of the three examinations. The anatomic T2W single-shot fast spin echo image used to guide MRS voxel placement is shown. MRS voxel and MRI region of interest locations are overlain as well as the corresponding PDFF values. Notice close agreement between all methods and examinations (collages for Figs. 1 and 2 created using Osirix 5.8 and Photoshop CS6).

Fig. 3

Linear regression of proton density fat fraction (PDFF) estimated by magnitude-based magnetic resonance imaging (MRI-M) and complex-based magnetic resonance imaging (MRI-C) against reference PDFF measured by magnetic resonance spectroscopy (MRS). Regression parameters are shown on the plot (Fig. 3 created using R 3.2.1 and re-sized in Photoshop CS6).