Quantitative shear elasticity imaging from a complex elastic wavefield in soft solids with application to passive elastography

In passive elastography, the complex physiological noise present in the human body is used to conduct an elastography experiment. In the present work, quantitative shear elasticity imaging from a complex elastic wavefield is demonstrated in soft solids. By correlating the elastic field at different positions, which can be interpreted as a time-reversal experiment, shear waves are virtually focused on any point of the imaging plane. According to the Rayleigh criterion, the focus size is directly related to the shear wave speed and thus to the shear elasticity. To locally retrieve a shear wave speed estimation, analytical and empirical expressions that relate the focus size with the shear wave speed and the frequency band used in the correlation computation are derived. The validity of such expressions is demonstrated numerically and experimentally on a tissue-mimicking phantom consisting of two different elastic layers. The obtained results were in complete agreement with a prior shear wave speed estimation demonstrating the potential of the technique to quantitative shear elasticity assessment using a complex elastic wavefield. Finally, an ultraslow experiment at an imaging rate of 10 Hz shows the technique to be compatible with slow imaging devices such as standard echographs or MRI scanners.