Sonoelasticity of organs: shear waves ring a bell.

Sonoelasticity is the use of ultrasonography to visualize, in real time, the hardness of stiffness of tissues and organs by depicting the tissue's motion in response to an applied vibration source. The applied vibration source is usually of low amplitude and low frequency (less than 0.1 mm displacement and less than 2000 Hz). Under these conditions, the natural vibration response of tissues and whole organs is revealed as a standing wave pattern determined by the low-frequency elastic constants of the tissues and their boundary conditions, factors that are not related to the ultrasonic echogenicity. As a result, hard or dense isoechoic tumors that are undetectable by conventional ultrasonography often can be visualized in sonoelasticity imaging by virtue of their altered vibration response. In this report, we demonstrate the appearance of organs such as the breast, liver, and kidney during real-time, in vivo sonoelasticity imaging. The results show that the shape and location of vibration patterns are dependent on the tissues and vibration frequencies; thus, information about the basic elastic properties of tissues should be obtainable.