Tissue shear elasticity assesment using time reversal.

Abstract

Shear waves in a soft solid can be focalized using time‐reversal (TR) methods. The wavelength depending on the elasticity of the medium is related to the focal spot width through the Rayleigh critera. This study proposes to quantitatively estimate the mechanical properties inside a 3‐D soft solid cavity from one channel TR experiments. Shear waves are created with an external low‐frequency (<300 Hz) mechanical excitation. The first step of the TR experiment consists in the observation of the forward reverberant elastic field; in a second step the backward field is computed in order to refocus the shear waves. Then the wavelength is deduced from the TR focus spot. Two methods for the observation step have been tested, the first one measuring one component of the vectorial field inside the solid by ultrasonic techniques developed in elastography. This method takes advantage of the ultrasound spatial accuracy and its robustness as regard to shear wave source allows to think about many applications in the medical field, including deep or moving organs. The second one is based on the surface wave measurement by acoustic sensors. This low‐cost method could be useful in food industry.Shear waves in a soft solid can be focalized using time‐reversal (TR) methods. The wavelength depending on the elasticity of the medium is related to the focal spot width through the Rayleigh critera. This study proposes to quantitatively estimate the mechanical properties inside a 3‐D soft solid cavity from one channel TR experiments. Shear waves are created with an external low‐frequency (<300 Hz) mechanical excitation. The first step of the TR experiment consists in the observation of the forward reverberant elastic field; in a second step the backward field is computed in order to refocus the shear waves. Then the wavelength is deduced from the TR focus spot. Two methods for the observation step have been tested, the first one measuring one component of the vectorial field inside the solid by ultrasonic techniques developed in elastography. This method takes advantage of the ultrasound spatial accuracy and its robustness as regard to shear wave source allows to think about many applications in the med...