Ultrasound shear wave elastography imaging with external mechanical vibration

Abstract

Ultrasound shear wave elastography (SWE) imaging is gaining wide acceptance in clinical practice as both a non-invasive and quantitative diagnostic modality. Most commercial SWE systems generate shear waves using acoustic radiation force (ARF), which requires complex hardware and is therefore only available on high-end and premium systems. External mechanical vibration (EMV) is an alternative to induce shear waves without expensive electronics, which potentially enables low-cost systems to provide SWE for point of care and low resource settings. In this thesis, an EMV concept of sinusoidally and synchronically vibrating two ball-shaped end-effectors to induce shear waves for real time SWE imaging was simulated, prototyped and tested. Finite element method (FEM) simulation and analysis shows the sinusoidal vibration generates shear waves that are constructive across the center plane of the two balls. By tracking the local displacement profiles at different depths of the center plane, shear wave speeds can be accurately estimated for different tissue stiffness. A mechatronic device using a voice coil actuator (VCA) to realize the EMV concept was prototyped. The mechanical vibrator was mounted on a commercial ultrasound probe and the vibration was synchronized with commercial ultrasound platform to induce shear waves as replacement of ARF. The generated shear waves were imaged by commercial ultrasonic systems to calculate shear wave speed and estimate tissue elasticity. Experimental data on liver phantoms under various vibration schemes demonstrated the capability of using this EMV device to conduct real-time SWE imaging that is comparable to ARF based systems.