[Fast technique to quantify liver steatosis at 3T: principles, parametric imaging and applications]

The purpose of this article is to present a fast and clinically usable technique for quantification of liver steatosis. This technique, based on a triple-echo gradient-echo sequence (in-phase, opposed-phase, in-phase), has recently been validated with excellent correlation and accuracy compared to proton MR spectroscopy. The theoretical principles are reviewed, with emphasis on the need to correct for the T2* decay inherent to the use of in-phase and opposed-phase sequences. T1 decay also is negligible due to the use of a low flip angle (20 degrees). The advantage of this technique is that it can generate a parametric representation (map) of liver steatosis, after fast and simple post-processing, based on measurements from standard images (addition, subtraction, division, multiplication) available on the MR scanning console. This parametric method allows quantification of steatosis in focal lesions. The main limitation of the technique relates to its ambiguity with lipid content over 50%, a phenomenon that does not occur with liver steatosis.