Local phase velocity imaging with wavenumber filter banks for ultrasound shear wave elastography

Ultrasound shear wave elastography is a non-invasive imaging technique for the assessment of the mechanical properties of tissues. However, existing techniques may yield erroneous assessments of lesion size or shape, particularly at low frequencies (250-500 Hz).

This study introduces a novel imaging technique, Local Phase Velocity-based Imaging utilizing Wavenumber-domain Bell Filters (LPVI-WBF), which enables the imaging of shear wave velocity in soft tissue at a single low frequency. This approach offers enhanced tissue lateral propagation and more precise stiffness measurements at low frequencies. Operating in the frequency-wavenumber domain, LPVI-WBF employs an adaptive approach that utilizes a custom two-dimensional Fourier transform and its inverse to enhance the phase velocity image smoothness with reduced time complexity and memory usage. In comparison with the original Local Phase Velocity-Based Imaging (LPVI) method, the LPVI-WBF has been demonstrated to reduce bias in phase velocity values at low frequencies (250-500 Hz) for stiffer inclusions which are of considerable significance in clinical contexts. Furthermore, a sliding window is not employed in LPVI-WBF due to the associated complications. In this study, both left-to-right and right-to-left acoustic radiation force pushes are employed to enhance the outcomes of a single push.

The results of our experiments with a heterogeneous elastic phantom demonstrate that proposed LPVI-WBF is an effective technique for reconstructing two-dimensional shear wave phase velocity maps with more accurate values and a higher contrast-to-noise ratio between target and background at low frequencies (i.e., below 500 Hz). Moreover, it reduces the processing time and memory usage by 39% and 94%, respectively.

This paper proposes a novel method for generating 2-D shear wave phase velocity images, resulting in local phase velocity maps that more accurately reflect the B-mode true shapes and values at low frequencies (i.e. below 500 Hz), as demonstrated by results obtained from inclusion phantoms. Additionally, LPVI-WBF provides a higher contrast-to-noise ratio (CNR) at low frequencies for stiffer inclusions, which are of great importance in clinical applications.