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3D strain estimation for isotropic and anisotropic materials

A study was undertaken to evaluate the feasibility of 3D strain imaging in muscle tissue. Simulations and phantom experiments were conducted for evaluation of iterative single-plane strain estimation algorithms. Rf-data is acquired with a 3D transducer (X4, Philips Sonos 7500) in bi-plane mode from the gelatin phantoms and a single volunteer’s calf muscle during passive compression. Iterative strain algorithms were applied using axial and non-axial correction and local stretching. The Field II simulation (a pre- and post-compression recording using artificially stretched scatterer positions (axial stretch: 1%; lateral stretch: 0.5%, cq. a Poisson-ratio of 0.5)) revealed excellent correlation between applied and measured axial strain. The phantom data showed similar results in both azimuth and lateral planes, although the Poisson’s ratio was slightly underestimated (0.46). Elastograms of the calf muscle showed different strain values in lateral and elevational direction due to the anisotropy of the calf muscle, despite the fact that the passive compression of the tissue was not optimal. 3D Elastography is feasible but further research is needed to improve lateral strain estimation and assess full-volume 3D strain.