Time Reversal Elastography: a correlation tomography of complex shear wave field in soft solids

National audienceShear waves in a soft solid can be focalized using time-reversal (TR) methods. The shear velocity, directly related to the elasticity of the medium, can be evaluated from the TR field. This study proposes to perform quantitative imaging of the mechanical properties inside a 3D soft solid cavity from TR experiments. Shear waves are created by finger impacts all over the surface of the solid. One component of the vectorial field inside the solid is measured by ultrasonic techniques developed in elastography. Inspired from Greens function retrieval methods, the TR field is computed from cross-correlation of this random-like displacement signal. One point is chosen as a virtual source where the spatio-temporal refocusing is observed. Thus the method allows focalisation of shear wave everywhere inside the solid without any source embedded in the solid. The local shear velocity is then deduced from the TR field. Finally a two dimensional velocity map of a bi-layer medium is performed using this method