The aim of this work was to validate a sequential method for quantifying the triglyceride fatty acid composition with 3.0 T MRI. The image acquisition was performed with a 3D spoiled gradient multiple echo sequence. A specific phase correction algorithm was implemented to correct the native phase images for wrap, zero- and first-order phase and rebuild the real part images. Then, using a model of a fat (1)H MR spectrum integrating nine components, the number of double bonds (ndb) and the number of methylene-interrupted double bonds (nmidb) were derived. The chain length (CL) was obtained from these parameters using heuristic approximation. Validations were performed on different vegetable oils whose theoretical fatty acid composition was used as reference and in five human subjects. In vivo measurements were made in the liver and in the subcutaneous and visceral adipose tissues. Linear regressions showed strong correlations between ndb and nmidb quantified with MRI and the theoretical values calculated using oil composition. Mean ndb/nmidb/CL were 1.80 ± 0.25/0.51 ± 0.21/17.43 ± 0.07, 2.72 ± 0.31/0.94 ± 0.16/17.47 ± 0.08 and 2.53 ± 0.21/0.84 ± 0.14/17.43 ± 0.07 in the liver, subcutaneous and visceral adipose tissues respectively. The results suggest that the triglyceride fatty acid composition can be assessed in human fatty liver and adipose tissues with a clinically relevant MRI method at 3.0 T.

Results showed that IVIM could be performed in free breathing, with a weighted-averaging procedure, a simultaneous diffusion gradient scheme and only four optimized b-values (0, 10, 80, and 800) reducing scan duration by a factor of nine compared with a nonoptimized protocol. Preliminary results have shown that parameters such as DSlow and DFast based on optimized IVIM protocol can be relevant biomarkers to distinguish between nonadvanced and advanced fibrosis.

The results of the current study indicate that the NNLS analysis in combination with biexponential curve fitting allows to correct for partial volume effects originating from blood flow in IVIM perfusion fraction measurements. Magn Reson Med 77:310-317, 2017. © 2016 Wiley Periodicals, Inc.

Purpose: To develop an MRI method for quantifying hepatic fat content and visceral adipose tissue fatty acid composition in mice on a 7.0T preclinical system. Methods: MR acquisitions were performed with a multiple echo spoiled gradient echo with bipolar readout gradients. After phase correction, the number of double bounds (ndb) and the number of methylene interrupted double bounds (nmidb) were quantified with a model including eight fat components, and parametric maps of saturated, monounsaturated, and polyunsaturated fatty acids were derived. The model included a complex error map to correct for the phase errors and the amplitude modulation caused by the bipolar acquisition. Validations were performed in fat-water emulsions and vegetable oils. In vivo, the feasibility was evaluated in mice receiving a high-fat diet containing primarily saturated fatty acids and a low-fat diet containing primarily unsaturated fatty acids. Results: Linear regressions showed strong agreements between ndb and nmidb quantified with MRI and the theoretical values calculated using oil compositions, as well as between the proton density and the fat fractions in the emulsions. At MRI, the mouse liver fat fraction was smaller in mice fed the low-fat diet compared with mice fed the high-fat diet. In visceral adipose tissue, saturated fatty acids were significantly higher, whereas monounsaturated and polyunsaturated fatty acids were significantly lower in mice fed the low-fat diet compared with mice fed the high-fat diet. Conclusion: It is feasible to simultaneously quantify hepatic fat content and visceral adipose tissue fatty acid composition with 7.0T MRI in mice. Magn Reson Med 76:510-518, 2016.

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.

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Background Overweight and obesity are major worldwide health concerns characterized by an abnormal accumulation of fat in adipose tissue (AT) and liver. Purpose To evaluate the volume and the fatty acid (FA) composition of the subcutaneous adipose tissue (SAT) and the visceral adipose tissue (VAT) and the fat content in the liver from 3D chemical‐shift‐encoded (CSE)‐MRI acquisition, before and after a 31‐day overfeeding protocol. Study Type Prospective and longitudinal study. Subjects Twenty‐one nonobese healthy male volunteers. Field Strength/Sequence A 3D spoiled‐gradient multiple echo sequence and STEAM sequence were performed at 3T. Assessment AT volume was automatically segmented on CSE‐MRI between L2 to L4 lumbar vertebrae and compared to the dual‐energy X‐ray absorptiometry (DEXA) measurement. CSE‐MRI and MR spectroscopy (MRS) data were analyzed to assess the proton density fat fraction (PDFF) in the liver and the FA composition in SAT and VAT. Gas chromatography‐mass spectrometry (GC‐MS) analyses were performed on 13 SAT samples as a FA composition countermeasure. Statistical Tests Paired t‐test, Pearson's correlation coefficient, and Bland–Altman plots were used to compare measurements. Results SAT and VAT volumes significantly increased (P < 0.001). CSE‐MRI and DEXA measurements were strongly correlated (r = 0.98, P < 0.001). PDFF significantly increased in the liver (+1.35, P = 0.002 for CSE‐MRI, + 1.74, P = 0.002 for MRS). FA composition of SAT and VAT appeared to be consistent between localized‐MRS and CSE‐MRI (on whole segmented volume) measurements. A significant difference between SAT and VAT FA composition was found (P < 0.001 for CSE‐MRI, P = 0.001 for MRS). MRS and CSE‐MRI measurements of the FA composition were correlated with the GC‐MS results (for ndb: rMRS/GC‐MS = 0.83 P < 0.001, rCSE‐MRI/GC‐MS = 0.84, P = 0.001; for nmidb: rMRS/GC‐MS = 0.74, P = 0.006, rCSE‐MRI/GC‐MS = 0.66, P = 0.020) Data Conclusion The follow‐up of liver PDFF, volume, and FA composition of AT during an overfeeding diet was demonstrated through different methods. The CSE‐MRI sequence associated with a dedicated postprocessing was found reliable for such quantification. Level of Evidence: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1587–1599.

• Non-invasive techniques to diagnose non-alcoholic fatty liver diseases (NAFLD) are important. • Liver fat volume fraction quantified using MRI correlates well with histology. • Fat volume fraction could be a relevant marker for NAFLD clinical follow-up. • Disjointed relaxation time estimation could potentially identify factors contributing to NAFLD.