P5D-2 Propagation of Narrowband Shear Waves Induced by a Finite-Amplitude Radiation Force

Localized low-frequency shear waves can be created by the dynamic radiation force resulting from two intersecting quasi-CW confocal ultrasound beams of slightly different frequencies. Such shear waves are narrowband rather than broadband and therefore, different frequency-dependent effects will not significantly affect their spectrum as they propagate through tissue. Nonlinear ultrasound propagation is assumed and the propagation of the generated shear waves at harmonic modulation frequencies is investigated using approximate viscoelastic Green´s functions [1]. Higher-viscosity conditions are also examined using exact solutions of the Green´s function. It is also shown how the Voigt-model parameters can be extracted from the shear dispersion, based on both the fundamental and second-harmonic shear component.