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Session: Ultrasound
Session starts: Thursday 26 January, 10:30
Presentation starts: 11:15
Room: Room 559

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Xueting Li ()
Simona Turco ()
Ronald M. Aarts ()
Hessel Wijkstra ()
Massimo Mischi ()

Abstract:
Shear wave (SW) elastography is an ultrasound imaging modality that provides quantitative measurements of tissue elasticity and viscosity, e.g., by k-space analysis of the SW velocity [1]. The estimated viscoelastic properties can be a suitable biomarker for the differentiation of benign and malignant tissue [2]. The phase difference method was introduced for the local assessment of the viscoelastic properties. In more detail, the phase difference of SWs measured at neighboring pixels is estimated through their temporal Fourier transform to derive a phase velocity dispersion plot, which is then interpreted by fitting a proper rheological model (e.g., Kelvin-Voigt model) [3]. While allowing for a local assessment of elasticity and viscosity, this method is very sensitive to noise. Therefore, a robust phase difference method, based on model-fitting in the time domain, is here proposed. Differently from the standard phase difference method, here a Prony fitting of the SW axial velocity is introduced [4], and a time delay is added to account for the SW arrival time at the measurement pixels. The dispersion plot is then calculated from the fitted signals at two laterally spaced pixels. By fitting a Kelvin-Voigt model to the dispersion plot, the elasticity and viscosity are estimated locally. A large fitting bandwidth is chosen to also enable the estimation of small viscosity, despite the higher noise levels. The proposed approach was tested and compared with the standard phase difference method in silico (MATLAB simulation) and in vitro, using a custom-made gelatin phantom measured by a Vantage 256 (Verasonics) system equipped with an L11-4v probe. The elasticity and viscosity with and without the proposed delayed Prony fitting in silico and in vitro were computed and compared. The reference values of the gelatin phantom were calculated by the standard k-space method, as the true values are unknown. In both cases, the delayed Prony fitting achieved smaller variations in both elasticity and viscosity compared with the standard phase difference method, which indicates its improved robustness to noise. [1] Palmeri et al., IEEE TUFFC, 2017 [2] Nenadic et al., Phys. Med. Biol., 2017. [3] Deffieux et al., IEEE TMI, 2009. [4] Kumaresan et al., Proc. IEEE, 1984.