Local phase velocity imaging (LPVI) as a new technique for shear wave elastography

Shear wave elastography is used in many clinical settings to measure the mechanical properties of soft tissues such as the liver, kidney, breast, and thyroid. In most implementations, the shear wave group velocity is measured using time-of-flight methods in the time-domain. However, different factors related to the estimation of the group velocity can cause variation in the results. Factors such as acquisition parameters, processing, tissue inhomogeneities and viscoelasticity can cause these variations. We propose to use methods that rely on phase velocities, shear wave velocities at specific frequencies, to standardize measurements across different clinical applications. We have developed methods for creating maps of phase velocity using Local Phase Velocity Imaging (LPVI). The LPVI method involves directional and wavenumber filtering before applying various steps of Fourier-based operations to obtain localized maps of phase velocity over large bandwidths. We will demonstrate how LPVI works in numerical data, tissue mimicking phantoms, and in vivo liver tissue. The LPVI method has enormous potential because the frequency, for which the phase velocity maps are reconstructed, can be controlled, optimized, and standardized for a wide array of clinical applications.