Improvements in Hepatic Stiffness Assessment with 3-D/3-axis MR Elastography

Introduction: MR Elastography (MRE) (1) is an MRI-based technique for quantitatively assessing the mechanical properties of soft tissues by studying the propagation of shear waves. Multiple studies (2-4) have reported on developments of MRE for assessing the viscoelastic properties of abdominal organs. In general, MRE inversion algorithms require datasets that sample the pattern of wave propagation in 3-D space, with acquisition of the x, y, and z components of motion at each point within the volume for multiple time points in the wave cycle. The acquisition time required to obtain 3-D data is lengthy and particularly inconvenient for abdominal imaging, where it is best to image during suspended respiration. Fortunately for hepatic MRE applications, there are situations in which the characteristics of the wavefield allow for optimized 2-D wave imaging capable of providing results in much shorter acquisition times (5,6). However, even in the liver, the largest abdominal organ, shear wave propagation can be complicated due to boundary and geometric effects which cause the 2-D wavefield model to break down in certain regions which limit its applicability for assessing hepatic tissue stiffness over the entire liver. Therefore, a practical 3-D MRE acquisition and inversion strategy is needed for improving the reliability of shear stiffness estimates in the abdomen. The purpose of this study was to evaluate a spin-echo multi-slice EPI MRE acquisition and 3-D local frequency estimation (LFE) approach for hepatic MRE compared to conventional 2-D MRE.