Investigating anisotropic elasticity using MR-Elastography combined with Diffusion Tensor Imaging: Validation using anisotropic and viscoelastic phantoms

Introduction: Magnetic Resonance Elastography (MRE) is a non-invasive imaging technique which is capable of quantifying soft tissue elasticity in vivo [1]. Most MRE studies have assumed isotropic mechanical properties although many soft tissues possess anisotropic mechanical properties due to their fibrous structure, for instance skeletal muscle or brain white matter. We propose a technique which for the first time combines Diffusion Tensor Imaging (DTI) information with MRE to investigate the anisotropic elasticity of tissue. By calculating the variation of diffusion of water molecules in different spatial directions, DTI can estimate the local fiber direction. Using this information, the shear modulus parallel (μ║) and perpendicular (μ┴) to the fiber can be calculated assuming a transversely isotropic model. Here, we aimed: 1) to design and construct anisotropic viscoelastic phantoms for validating the combined MRE/DTI imaging technique. 2) To quantitatively validate this combined MRE/DTI technique by comparing the anisotropic ratio (μ║/μ┴) of the MRE results with the “gold standard” rotational rheometry results. Once fully validated, this technique could potentially shed new light on tissue injury mechanisms. Diseases such as multiple sclerosis and atrophy are known to be associated with changes in tissue anisotropy. It could also provide additional physical parameters to help the development of more accurate computer models.