Simultaneous MR quantification of hepatic fat content, fatty acid composition, transverse relaxation time and magnetic susceptibility for the diagnosis of non‐alcoholic steatohepatitis

Abstract

Non-alcoholic steatohepatitis (NASH) is characterized at histology by steatosis, hepatocyte ballooning and inflammatory infiltrates, with or without fibrosis. Although diamagnetic material in fibrosis and inflammation can be detected with quantitative susceptibility imaging, fatty acid composition changes in NASH relative to simple steatosis have also been reported. Therefore, our aim was to develop a single magnetic resonance (MR) acquisition and post-processing scheme for the diagnosis of steatohepatitis by the simultaneous quantification of hepatic fat content, fatty acid composition, T * transverse relaxation time and magnetic susceptibility in patients with non-alcoholic fatty liver disease. MR acquisition was performed at 3.0 T using a three-dimensional, multi-echo, spoiled gradient echo sequence. Phase images were unwrapped to compute the B field inhomogeneity (ΔB ) map. The ΔB -demodulated real part images were used for fat-water separation, T * and fatty acid composition quantification. The external and internal fields were separated with the projection onto dipole field method. Susceptibility maps were obtained after dipole inversion from the internal field map with single-orientation Bayesian regularization including spatial priors. Method validation was performed in 32 patients with biopsy-proven, non-alcoholic fatty liver disease from which 12 had simple steatosis and 20 NASH. Liver fat fraction and T * did not change significantly between patients with simple steatosis and NASH. In contrast, the saturated fatty acid fraction increased in patients with NASH relative to patients with simple steatosis (48 ± 2% versus 44 ± 4%; p < 0.05) and the magnetic susceptibility decreased (-0.30 ± 0.27 ppm versus 0.10 ± 0.14 ppm; p < 0.001). The area under the receiver operating characteristic curve for magnetic susceptibility as NASH marker was 0.91 (95% CI: 0.79-1.0). Simultaneous MR quantification of fat content, fatty acid composition, T * and magnetic susceptibility is feasible in the liver. Our preliminary results suggest that quantitative susceptibility imaging has a high diagnostic performance for the diagnosis of NASH.

Accurate fatty acid composition estimation of adipose tissue in the abdomen based on bipolar multi‐echo MRI

“…(4) Approximate maps for the field map and , which were calculated using conventional multi‐echo water‐fat separation assuming fixed fat peak amplitudes, were used to initialize a nonlinear procedure that jointly estimates confounding factors and the FAC on a voxel‐by‐voxel basis. Essentially, the method can thus be considered as a combination of the earlier stepwise and joint approaches.…”

“…For example, quantification of liver fat deposition alone poorly separates NAFLD from nonalcoholic steatohepatitis (NASH) . However, there is emerging evidence that characterizing the FAC (i.e., the fractions of unsaturated (UFA), saturated (SFA), mono‐unsaturated (MUFA) and poly‐unsaturated (PUFA) fatty acids with regard to the total fat content) may yield more insights into disease states . Particularly in patients with NAFLD and NASH, both quantification of liver fat deposition and characterization of the types of fatty acid chains in the extrahepatic fat depots is of interest .…”

“…MR spectroscopy (MRS) based approaches quantify the triglyceride saturation state by fitting Gaussian or Lorentzian lineshapes to the measured fat peaks of a 1 H MR spectrum . Since the distribution of fatty acids in various adipose fat compartments is potentially different, MRI‐based FAC methods that provide spatially resolved 3‐D parameter maps and incorporate information about the chemical triglyceride structure are of special interest . As the data are acquired at several discrete echo time points, MRI‐based methods are limited in terms of spectral resolution, and robust estimation of the confounder‐corrected signal model parameters can be challenging in the presence of image noise .…”

“…As the data are acquired at several discrete echo time points, MRI‐based methods are limited in terms of spectral resolution, and robust estimation of the confounder‐corrected signal model parameters can be challenging in the presence of image noise . This has been addressed in the past by applying long acquisition times to acquire images with sufficient SNR, or by estimating unknown parameters sequentially to improve the noise propagation behavior of the quantification procedure . Additionally, confounding effects of bipolar readout gradients and T 1 weighting on FAC estimates have been analyzed and addressed.…”

3T chemical shift‐encoded MRI: Detection of altered proximal femur marrow adipose tissue composition in glucocorticoid users and validation with magnetic resonance spectroscopy

“…Recent advances in water‐fat imaging methods allows discrimination between different types of fat in terms of their amount of saturation (saturated fat fraction, SFA), poly‐unsaturation (poly‐unsaturated fat fraction, PUFA) and mono‐unsaturation (mono‐unsaturated fat fraction, MUFA). This approach has been validated using MRS in liver, adipose tissue, muscle, bone marrow, and more recently in abdominal adipose tissue using gas chromatography …”