Shear Wave Speed Measurements Using Crawling Wave Sonoelastography and Single Tracking Location Shear Wave Elasticity Imaging for Tissue Characterization

Abstract

Elastography provides tissue stiffness information that attempts to characterize the elastic properties of tissue. However, there is still limited literature comparing elastographic modalities for tissue characterization. This study focuses on two quantitative techniques using different vibration sources that have not been compared to date: crawling wave sonoelastography (CWS) and single tracking location shear wave elasticity imaging (STL-SWEI). To understand each technique's performance, shear wave speed (SWS) was measured in homogeneous phantoms and ex vivo beef liver tissue. Then, the contrast, contrast-to-noise ratio (CNR), and lateral resolution were measured in an inclusion and two-layer phantoms. The SWS values obtained with both modalities were validated with mechanical measurements (MM) which serve as ground truth. The SWS results for the three different homogeneous phantoms (10%, 13%, and 16% gelatin concentrations) and ex vivo beef liver tissue showed good agreement between CWS, STL-SWEI, and MM as a function of frequency. For all gelatin phantoms, the maximum accuracy errors were 2.52% and 2.35% using CWS and STL-SWEI, respectively. For the ex vivo beef liver, the maximum accuracy errors were 9.40% and 7.93% using CWS and STL-SWEI, respectively. For lateral resolution, contrast, and CNR, both techniques obtained comparable measurements for vibration frequencies less than 300 Hz (CWS) and distances between the push beams ( ∆x ) between 3 mm and 5.31 mm (STL-SWEI). The results obtained in this study agree over an SWS range of 1-6 m/s. They are expected to agree in perfectly linear, homogeneous, and isotropic materials, but the SWS overlap is not guaranteed in all materials because each of the three methods have unique features.

The biomechanics of simple steatosis and steatohepatitis

“…These conventional mechanical measurements were considered the reference when assessing the elasticity properties of the cylindrical phantom. Similar to Zhang et al (2007) and Ormachea et al (2016), the stress relaxation curve of each sample was fitted to the Kelvin-Voigt fractional derivative (KVFD) model using standard nonlinear least squares procedures. This viscoelastic model contains three parameters: E 0 , ζ, and a. E 0 refers to the relaxed elastic constant, ζ refers to the viscoelastic parameter, and a refers to the order of fractional derivative.…”

Plane-Wave Imaging Improves Single-Track Location Shear Wave Elasticity Imaging

“…Using the Nyquist sampling theorem, we estimate that SWEI should be performed with a minimum frame rate of 2 kHz. We based this estimate on published results that demonstrate that shear waves contain significant spectral components up to 1 kHz [22]. Averaging that improves pSTL-SWEI cannot be applied to MTL-SWEI to the same effect.…”

“…We defined CNR e as follows [22]: $$CN{R}_e=\frac{|{\mu }_L-{\mu }_B|}{\sqrt{{\sigma }_L^2+{\sigma }_B^2}}$$ where μ L and μ Β represent the mean SWS in the inclusion and surrounding tissue respectively; and σ L and σ Β represent the variance of SWS in the inclusion and surrounding tissue respectively.…”

Spring–damper equivalents of the fractional, poroelastic, and poroviscoelastic models for elastography

“…() Publications report observed values for the exponent, α , in the range 0.06–0.27 for ultrasound elastography in liver and prostate and 0.26–0.3 for MR elastography of liver. Similarly, Ormachea et al demonstrated that such low values of α are consistent between different ultrasound elastography methods in liver.…”

“…since 22 = f , 39 where is a structure constant related to tortuosity. Comparison with Equations 12 and 13 shows that Equations 29 and 30 are exactly the same as those of the Zener model.…”