Doppler ultrasound detection of shear waves remotely induced in tissue phantoms and tissue in vitro

Abstract

In shear wave elasticity imaging (SWEI), mechanical excitation within the tissue is remotely generated using radiation force of focused ultrasound. The induced shear strain is subsequently detected to estimate visco-elastic properties of tissue and thus aid diagnostics. In this paper, the mechanical response of tissue to radiation force was detected using a modified ultrasound Doppler technique. The experiments were performed on tissue mimicking and tissue containing phantoms using a commercial diagnostic scanner. This scanner was modified to control both the pushing and probing beams. The pushing beam was fired repetitively along a single direction while interlaced probing beams swept the surrounding region of interest to detect the induced motion. The detectability of inhomogeneous inclusions using ultrasonic Doppler SWEI method has been demonstrated in this study. The displacement fields measured in elastic phantoms clearly reveal the oscillatory nature of the mechanical relaxation processes in response to impulsive load due to the boundary effects. This relaxation dynamics was also present in cooked muscle tissue, but was not detected in more viscous and less elastic phantom and raw muscles. Presence of a local heterogeneity in the vicinity of the focal region of the pushing beam results in generation of a standing wave field pattern which is manifested in the oscillatory response of the excited region of the tissue. There has been made an assumption that dynamic characteristics of the relaxation process may be used for visualization of inhomogeneities.