Combination of liver intravoxel incoherent motion imaging with MR fat quantification at 3.0 T to distinguish between pure steatosis and NASH
Résumé
Purpose: To evaluate the combination of liver intra-voxel incoherent motion imaging (IVIM) and a MRI fat quantification method at 3.0 T to make the distinction between NASH and pure steatosis. Methods and Materials: A multi-angle multi-gradient echo acquisition combined with a dedicated algorithm was used to quantify liver fat volume fraction (FVF), corrected for water and fat relaxation times and accounting for the NMR spectrum of fat. IVIM was performed using a single-shot SE-EPI sequence, in free breathing, with 11 b-values (0-20-40-60-80-100-200-300-400-600-800s.mm-2) and a weighted signal averaging procedure. Three orthogonal diffusion gradients were sequentially applied. A 2000 ms TR, 54 ms minimum TE; 21 axial slices of 8 mm thick; 400×300 mm² FOV; 128×96 matrix were used. IVIM parameters (pure molecular diffusion coefficient (DSlow), perfusion-related diffusion coefficient (DFast) and perfusion fraction (f)) were estimated. MR imaging was performed on a healthy volunteers group (n=33), and on patients with histologically confirmed pure steatosis (n=16) or NASH (n=4). Results: Wilcoxon test showed that DSlow was significantly lower when fat is present (FVF > 5.5%) (p < 0.01). DSlow and DFast were found significantly reduced between subjects with pure steatosis (Brunt=0) and NASH (Brunt> 0) (p < 0.05). Conclusion: Fat vesicles in pure steatosis restrict molecular diffusion without modification of micro-perfusion. In NASH, fibrosis still increase the restriction of molecular diffusion compared to patients with pure steatosis and decrease the microperfusion as illustrated by the decrease of perfusion-related diffusion coefficient. These preliminary results suggest that combining MRI fat quantification and IVIM could be a none invasive mean to distinguish between pure steatosis and NASH.