Complex stiffness quantification using ultrasound stimulated vibrometry

The propagation speed of shear waves is related to frequency and the complex stiffness (shear elasticity and viscosity) of the medium. A method is presented to solve for complex stiffness of a homogeneous medium by measuring shear wave speed dispersion. Harmonic radiation force, introduced by modulating the energy density of incident ultrasound, is used to generate shear waves of various frequencies in a homogeneous medium. The speed of shear waves is measured from phase shift detected over the distance propagated. Measurements of shear wave speed at multiple frequencies are fit with the theoretical model to solve for the shear elasticity and viscosity of the medium. A laser vibrometer is used in experiments to detect the vibration within gelatin phantoms, which shows promising results validated by an independent complex-stiffness quantification method. Practical considerations and challenges in possible medical applications are discussed.