The Impact of Acoustic Radiation Force Excitation Geometry on ShearWave Dispersion and Attenuation Estimates

摘要

Shear wave elasticity imaging (SWEI) characterizes the mechanical properties of human tissues to differentiate healthy from diseased tissue. Commercial scanners tend to reconstruct shear wave speeds for a region of interest using time-of-flight methods reporting a single shear wave speed (or elastic modulus) to the end user under the assumptions that tissue is elastic and shear wave speeds are not dependent on the frequency content of the shear waves. Human tissues, however, are known to be viscoelastic, resulting in dispersion and attenuation. Shear wave spectroscopy and spectral methods have been previously presented in the literature to quantify shear wave dispersion and attenuation, commonly making an assumption that the acoustic radiation force excitation acts as a cylindrical source with a known geometric shear wave amplitude decay. This work quantifies the bias in shear dispersion and attenuation estimates associated with making this cylindrical wave assumption when applied to shear wave sources with finite depth extents, as commonly occurs with realistic focal geometries, in elastic and viscoelastic media. Bias is quantified using analytically-derived shear wave data and shear wave data generated using finite element method models. Shear wave dispersion andattenuation bias (up to 15% for dispersion and 41% for attenuation) is greaterfor more tightly-focused acoustic radiation force sources with smaller depths offield relative to their lateral extent (height-to-width ratios < 16).Dispersion and attenuation errors associated with assuming a cylindricalgeometric shear wave decay in SWEI can be appreciable and should be consideredwhen analyzing the viscoelastic properties of tissues with acoustic radiationforce source distributions with limited depths-of-field.