| Measurement of liver elasticity (i.e., stiffness) can be used as a noninvasive alternative to liver biopsy to stage liver fibrosis, a condition afflicting hundreds of millions of patients worldwide. Quantitative measurement of stiffness (in unit of Pascal) is required 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. Shearwave Dispersion Ultrasound Vibrometry (SDUV) uses shear wave propagation speed measured in tissue at multiple frequencies (typically in the range of hundreds of Hertz) to solve quantitatively for both tissue elasticity and viscosity. A shear wave is stimulated within the tissue by an ultrasound push beam and monitored by a separate ultrasound detect beam. The phase difference of the shear wave between two locations along its propagation path is used to calculate shear wave speed within the tissue. An intermittent pulse sequence is developed to facilitate one array transducer for both push and detect function. Feasibility of this pulse sequence is demonstrated by SDUV measurements in porcine liver using both a dual transducer prototype and a modified commercial ultrasound scanner. |