Speckle-free estimation of tissue elasticity with single track location shear wave elasticity imaging

Abstract

Shear Wave Elasticity Imaging (SWEI) is commonly used to characterize tissue elasticity, but conventional, multiple-track-location SWEI (MTL-SWEI) techniques are resolution-limited by speckle. MTL-SWEI techniques use plane wave ultrasound to monitor an induced shear wave as it propagates across a set of tracking beams within a region of interest. The scattering process creates a random, yet stationary, spatial sensitivity pattern for each beamformed location, called speckle bias, which causes errors in MTL-SWEI shear wave speed estimates that cannot be improved through averaging. Single Track Location SWEI (STL-SWEI) overcomes speckle bias by using a single track beam, subsequently exciting and tracking different push locations, and comparing the timing of the recorded shear wave signals from different push locations to estimate shear wave speed. Two and three-dimensional STL-SWEI imaging techniques are presented and compared to MTL-SWEI and Acoustic Radiation Force Impulse (ARFI) imaging in phantoms and in vivo experiments. Tradeoffs and techniques for sequencing, beamforming, shear wave speed estimation, and image formation are discussed. For applications where tissue heating and motion are not limiting factors, STL-SWEI provides superior imaging in terms of lateral resolution and contrast-to-noise ratio compared to MTL-SWEI and ARFI. [This work was supported by NIHR37HL096023 and NIHR01EB01248.]Shear Wave Elasticity Imaging (SWEI) is commonly used to characterize tissue elasticity, but conventional, multiple-track-location SWEI (MTL-SWEI) techniques are resolution-limited by speckle. MTL-SWEI techniques use plane wave ultrasound to monitor an induced shear wave as it propagates across a set of tracking beams within a region of interest. The scattering process creates a random, yet stationary, spatial sensitivity pattern for each beamformed location, called speckle bias, which causes errors in MTL-SWEI shear wave speed estimates that cannot be improved through averaging. Single Track Location SWEI (STL-SWEI) overcomes speckle bias by using a single track beam, subsequently exciting and tracking different push locations, and comparing the timing of the recorded shear wave signals from different push locations to estimate shear wave speed. Two and three-dimensional STL-SWEI imaging techniques are presented and compared to MTL-SWEI and Acoustic Radiation Force Impulse (ARFI) imaging in phantoms and ...