Understanding Shear Waves in Skeletal Muscle: Refining Elastography though Finite Element Analysis

Elastography is a form of medical imaging that attempts to measure tissue material properties through the imaging of propagating shear waves. The technique was born from the idea of palpation and that pathologic changes to tissue will manifest as changes in stiffness. However, shear wave propagation in complex structures does not always have a readily solvable solution, and therefore it is difficult to predict how these waves will travel in tissues like the brain, skeletal muscle, and the heart. To circumvent this issue, many researchers apply assumptions that limit the complexity of analysis and make the mathematical connection between wave dynamics and material properties solvable. These assumptions have historically been that biological tissue is isotropic, homogeneous, and without prestress. This, however, is far from the truth in many tissues, and so the estimates of material properties are not accurate. Explicit modeling of the fibrous muscle through Diffusion Tensor Imaging (DTI) allows for more robust FEA and proper inclusion of prestressed wave motion. The presented work discusses the foundational concepts in engineering and physiology and leads to two published papers asserting future theoretical considerations necessary for elastography in muscle, and finally a novel DTI to FEA modeling algorithm to be used for further studies. This work will help in develop better inversion algorithms that incorporate prestress, anisotropy, and heterogeneity, therefore improving the accuracy of muscle viscoelastic material estimates.