Methods

Patients: Twenty-five patients with hepatic steatosis (alcoholic or non-alcoholic) diagnosed by histopathology after biopsy will be submitted to a MRS examination as well as to DWI and DEI exams. Urine and blood samples will be collected beforehand in order to perform bioassays and metabonomics studies. 

Controls: Six healthy volunteers will be recruited to optimize the MR techniques. Twnty-five healthy subjects will undergo the same MR tests as the patients.

Bioassays and metabonomics: The ALT and AST activities, the lipidic profile as well as other biochemical parameters will be measured on the blood sample. NMR spectra of urine and blood extracts will be recorded at high field for metabonomics.

MRS/MRI exams: Three MR examinations will be carried out at a magnetic field of 1.5 T. All acquisitions will be performed with breathholding. Total exam duration will be approximately 30 minutes.

Magnetic Resonance Spectroscopy (MRS): MR spectra will be recorded in three different 8 cc voxels (superior lobe, middle and inferior lobe of the liver). Spectra will be treated and analyzed by the LCModel software to obtain the lipid/water ratio.

Diffusion-Weighted Imaging (DWI): Diffusion-weighted images will be obtained on axial sections covering all the liver. The apparent diffusion coefficient (ADC) of water will be calculated in various areas using FUNCTOOL software.

             DWI of the liver without any gradient    DWI of the liver with a diffusion gradient

DWI images example of the liver (located in the left part of each images). The left image is a T2 image where no gradient is applied. The right image contains a gradient with a value of b = 100 mm/s2. DWI is used to measure the passive water movement in an organ.

Double-Echo Imaging (DEI): Two series of images will be acquired, where the protons are in phase and out of phase respectively, on 16 axial slices. The Dixon method will be used to calculate the fraction of fat present within the liver as well as the steatosis index.

             Image en double-écho (IDÉ) où tous les protons sont en phase   Image en double-écho (IDÉ) où tous les protons sont hors phase.

DEI images of the liver. The left and right images are acquired with a gradient that aligns all the protons in the same direction (in phase) and in opposite directions (out of phase), respectively . The fat fraction is calculated from these images.