Identification of Anisotropic Material Parameters in Elastic Tissue Using Magnetic Resonance Imaging of Shear Waves

This paper describes the application of a material parameter identification method based on elastic shear wave propagation to simulated and experimental data from magnetic resonance elastography (MRE). In MRE, the displacements of traveling transverse and longitudinal waves in elastic, biological tissue are captured as complex 3D images. Typically, the magnitude of these waves is small, and the equations of waves in linear elastic media can be used to estimate the material properties of tissue, such as internal organs, muscle, and the brain. Of particular interest are fibrous tissues which have anisotropic properties. In this paper, an anisotropic material model with three material parameters (shear modulus, shear anisotropy, and tensile anisotropy) is the basis for parameter identification. This model relates shear wave speed, propagation direction, and polarization to the material properties. A directional filtering approach is applied to isolate the speed and polarization of shear waves propagating in multiple directions. The material properties are then estimated from the material model and isolated shear waves using weighted least squares.