 ARFI US is a novel technique, recently FDA approved for use in children and adults, which provides an alternative method for quantifying liver stiffness. ARFI US has been shown in a small pilot investigation in Europe in children to be reliable and rapid in estimating moderate to severe liver stiffness using histology as a reference gold standard. ARFI measures the speed of a shear wave in the examined tissue, expressed in ms. This shear wave velocity can be mathematically converted into a liver stiffness value, which can then be used to estimate degree of liver fibrosis. The technique is non-invasive, uses no ionizing radiation, and is fast several minutes to complete. It is possible that ARFI US will be more accurate than MRE in quantifying liver stiffness. In addition, ARFI US will ultimately be a less expensive clinical test, shorter in duration, and will not require sedationanesthesia in younger children as MRE requires. 