Focused shear wave beams for enhanced soft tissue elastography

The elastic response of soft tissues at audio frequencies is closely associated with disease-related changes in tissue microstructure and function. The propagation speed of shear waves in tissue, which is related to the shear modulus, is used to map tissue stiffness noninvasively, for example to assess breast lesion malignancy and liver disease severity. Conventional approaches for shear wave excitation are based on the acoustic radiation force or vibration of a small piston on the skin, both of which generate small-amplitude, diverging shear waves, and are limited in their ability for penetration to the required depths, especially in the assessment of liver stiffness because liver disease is often associated with obesity. Our group conceived and realized experimentally focused shear wave beams, generated by vibration of a concave piston source, which converge toward the measurement region, thereby maintaining high amplitude at the required depths. An overview is presented of recent progress in the application of focused shear wave elastography in the context of fatty liver disease assessment. Recent advances in the prediction of nonlinear effects in shear wave beam propagation will also be discussed. [P.G.K. was supported by the Chester M. McKinney Graduate Fellowship in Acoustics at ARL:UT.]