Ultrafast compound imaging for 2-D motion vector estimation: application to transient elastography

TLDR

Transient elastography has so far measured only axial displacements induced by low‑frequency vibrators, while the technique could also benefit color flow and reflectivity imaging. The study introduces a high‑frame‑rate 2‑D ultrasound motion‑vector imaging technique to track both axial and lateral displacements during shear‑wave propagation, aiming to enhance Young’s modulus reconstruction. The method employs a single plane‑wave, ultra‑fast insonification with receive‑mode beamforming on two subapertures, followed by 1‑D speckle tracking of successive decorrelated speckle patterns to estimate axial and lateral displacements. Experimental results demonstrate the technique’s potential for transient elastography.

Abstract

This paper describes a new technique for two-dimensional (2-D) imaging of the motion vector at a very high frame rate with ultrasound. Its potential is experimentally demonstrated for transient elastography. But, beyond this application, it also could be promising for color flow and reflectivity imaging. To date, only axial displacements induced in human tissues by low-frequency vibrators were measured during transient elastography. The proposed technique allows us to follow both axial and lateral displacements during the shear wave propagation and thus should improve Young's modulus image reconstruction. The process is a combination of several ideas well-known in ultrasonic imaging: ultra-fast imaging, multisynthetic aperture beamforming, 1-D speckle tracking, and compound imaging. Classical beamforming in the transmit mode is replaced here by a single plane wave insonification increasing the frame rate by at least a factor of 128. The beamforming is achieved only in the receive mode on two independent subapertures. Comparison of successive frames by a classical 1-D speckle tracking algorithm allows estimation of displacements along two different directions linked to the subapertures beams. The variance of the estimates is finally improved by tilting the emitting plane wave at each insonification, thus allowing reception of successive decorrelated speckle patterns.