Liver elasticity and viscosity quantification using shearwave dispersion ultrasound vibrometry (SDUV)

Noninvasive quantification of liver elasticity is a promising alternative to liver biopsy to stage liver fibrosis, a condition afflicting hundreds of millions of patients worldwide. Quantitative measurement of elasticity (in unit of Pascal) is required in this application because liver fibrosis is a diffuse disease where abnormality is not confined to a local region and there is no normal background tissue to provide contrast. SDUV uses an ultrasound ldquopushrdquo beam to stimulate formation of propagating harmonic shear waves in the studied tissue. The propagation speed of induced shear waves is frequency dependent (dispersive) and relates to the tissue´s mechanical properties. Shear wave speeds at multiple frequencies (typically hundreds of Hertz) are measured by a separate ultrasound ldquodetectrdquo beam in pulse echo mode and fit with a theoretical dispersion model to inversely solve for tissue elasticity and viscosity. A special pulse sequence has been developed to facilitate a single ultrasound array transducer for both push and detect function, which makes SDUV compatible with current ultrasound scanners. Feasibility of this pulse sequence is demonstrated by in vivo SDUV measurements in porcine liver using a dual transducer prototype.