Estimation of the phase velocity dispersion curves for viscoelastic materials using Point Limited Shear Wave Elastography.

Ultrasound shear wave elastography (SWE) is widely used in clinical applications for non-invasive measurements of soft tissue viscoelasticity. The study of tissue viscoelasticity often involves the analysis of shear wave phase velocity dispersion curves, which show how the phase velocity varies with frequency or wavelength. In this study, we propose an alternative method to the two-dimensional Fourier transform (2D-FT) and Phase Gradient (PG) methods for shear wave phase velocity estimation. We introduce a new method called Point Limited Shear Wave Elastography (PL-SWE), which aims to reconstruct phase velocity dispersion curves using a minimal number of measurement points in the spatial domain (as few as two signals can be utilized). We investigated how the positioning of the first signal and the distance between selected signals affect the shear wave velocity dispersion estimation in PL-SWE. The effectiveness of this novel approach was evaluated through the analysis of analytical phantom data in viscoelastic media, along with experimental data from custom-made tissue-mimicking elastic and viscoelastic phantoms, and in vivo renal transplant data. A comparative analysis with the 2D-FT technique revealed that PL-SWE provided phase velocity dispersion curve estimates with root mean squared percentage error (RMSPE) values of less than 1.61% for analytical phantom data, 1.58% for elastic phantoms, 4.29% for viscoelastic phantoms and 7.68% for in vivo data, while utilizing significantly fewer signals compared to 2D-FT. The results demonstrate that the PL-SWE method also outperforms the PG method. For the viscoelastic phantoms, the mean RMSPE values using PL-SWE ranged from 2.61% to 4.29%, while the PG method produced RMSPE values between 3.56% and 15%. In the case of in vivo data, PL-SWE yielded RMSPE values between 7.01% and 7.68%, while PG results ranged from 17% to 418%. These findings highlight the superior accuracy and reliability of the PL-SWE method, particularly when compared to the PG approach. Our tests demonstrate that PL-SWE can effectively measure the phase velocity of both elastic and viscoelastic materials and tissues using a limited number of signals. Utilizing a minimal number of spatial measurement points could enable accurate assessments even in cases with restricted field of view, thereby expanding the applicability of SWE across various patient populations.