Is ultrasonic imaging a sensitive indicator of spatially varying elastic anisotropy?

It has been conjectured that the mechanical structure of some early-forming neoplasms is anisotropic. If true then strain imaging at different scan angles may provide important diagnostic features for accurate classification of early malignant disease. We are assessing the capability of strain imaging for sensing directionally dependent soft-tissue elastic properties. The studies include measurements and FEA models of gelatin phantoms and ex vivo bovine skeletal muscle. Passive muscle deformation is nonlinear, viscoelastic, and transverse isotropic, in stark contrast to the reference gelatin materials that are isotropic, Hookean solids at very low cycling frequency. We found that for elastically heterogeneous tissue-like media, differences in elastic constants smaller than a factor of two were observed. However changes in directionally-dependent geometry and boundary conditions compete with material anisotropy and are difficult to distinguish. The role of strain imaging for detecting elastic anisotropy depends on the separability of these effects.