Non-invasive imaging of diffuse liver disease using water T2 and fat fractions obtained from a breath hold radial GRASE method

Introduction: The diagnosis of inflammation, fibrosis, and steatosis is important in the characterization of diffuse liver disease such as Hepatitis C, nonalcoholic steatosis (NASH), and cirrhosis. Currently the diagnosis of these pathologies requires a liver biopsy which is an invasive procedure with associated morbidity and cost and in some cases subject to sampling errors. Non-invasive imaging techniques including Magnetic Resonance Elastography and Diffusion Weighted MRI have been sought as a means to provide a non-invasive alternative for the diagnosis of diffuse liver disease [1,2]. One of the drawbacks of these techniques is that the presence of fat (typically found in the liver as a results of the above mentioned liver pathologies) is a confounding factor in the determination of parameters that otherwise can be associated with inflammation and fibrosis. Recently our group developed a novel radial gradient and spin-echo (GRASE) method which provides T2 and fat-water mapping with the advantage that the T2 estimation is independent of the presence of fat [3,4]. The method is fast (data for T2 and fat-water mapping are acquired in a breath hold) and it provides high spatial resolution and motion insensitivity. These conditions make it ideal for liver imaging. In this work we provide the first results in patients with various liver conditions and compare T2 and fat-water information to biopsy results. Methods: A radial GRASE pulse sequence was implemented on a 1.5T GE Signa NV-CV/i scanner. In the radial GRASE method used in this study four gradient echoes were collected at each SE period. Data were acquired on a breath hold (18 s) with BW=±125 kHz, ETL=12, matrix size=256×192, TR=1s, NEX=1. Time shifts between the SE points and the four gradient echoes corresponded to fat-water phase shifts of (-5π/2, -π/6, π/2, 7π/6). The procedure used for T2 and fat-water mapping is as follows. First, the four gradient echoes are used to obtain initial fat-water estimates, corrected for the effects of field inhomogeneities, using an iterative fat-water decomposition method [5]. For T2 estimation we use the gradient echoes that are closest to the SE point to generate images at various TEeff as described recently in [3]. T2 of the water component, T2w, and the final fat-water estimates were then calculated by fitting the signal intensity of every pixel in the TEeff images (i.e. 12 images) to: