In-plane anisotropy method for the characterization of the elastic properties of anisotropic materials

Acoustic radiation force-based methods have the ability of estimating tissue viscoelastic material properties. A limitation of the current methods exists when the estimation of the mechanical properties is performed under the assumption that the tissue is isotropic and homogeneous thus, neglecting the inherent anisotropy nature of certain tissues. Currently to facilitate the estimation of the elastic parameters of these types of tissues, it is common to assume that these anisotropic biological media can be modeled as being transversely isotropic (TI). Based on this assumption mechanical properties of these tissues are evaluated by measuring the shear wave velocity at different angles by rotating the tissue with respect to the transducer, where 0° and 180° are defined along the fibers, and 90° and 270° across the fibers. The characterization of the behavior of anisotropic materials by the abovementioned method presents numerous limitations that can be overcome by a simplified approach to estimate the TI shear moduli by measuring the shear waves in a single B-mode imaging plane. We refer to this method as In-Plane Anisotropy (IPA) technique. To investigate the feasibility of the IPA method, we used a finite element model (FEM) of the shear wave propagation in an elastic TI media, and we evaluated the anisotropic characteristics of a phantom incorporating fibrous material with preferential orientations and a sample of pork tenderloin.