Vasconcelos, Luiz

Ultrasound shear wave elastography (SWE) is a useful technique for non-invasive tissue assessment. For effective quantitative analysis the employment of physical models is necessary for rheological parameter estimation, such as the Kelvin-Voigt (KV) model. From SWE data, the frequency response can be calculated, and the shear wave velocity dispersion can be fit, yielding the shear elasticity and shear viscosity, μ1 and μ2, respectively. In this study, a parametric evaluation is performed using staggered-grid finite-difference simulations of materials with μ1 = 1–25 kPa (increment: 1 kPa) and μ2 = 0–10 Pa s (increment: 0.5 Pa s), with an acoustic radiation force push of f-number equal to 2. The novel Stockwell transform combined with a slant frequency-wavenumber analysis (GST-SFK) was compared with the two-dimensional Fourier transform for dispersion curve estimation over a variety of frequency ranges. Regardless of dispersion curve estimation technique, the accuracy of estimating μ1 is confounded for μ2 values above 5 Pa s. It was found that KV fitting benefits from wider frequency ranges (up to 1kHz), with lower μ1 and μ2 estimation errors. The GST-SFK was the best dispersion curve calculation technique, yet the KV fitting process was found to be unreliable for parameter estimation in highly viscous media.

End-stage kidney disease is the result of progressive declines in function and frequently requires a transplant. Maintaining kidney transplant health with regularly scheduled function tests or biopsies is necessary to adjust treatments. Ultrasound shear wave elastography (SWE) could provide an inexpensive, noninvasive modality to monitor allograft health. In this project, we built models of the kidney cortex from segmented kidney transplant histology images. We assigned viscoelastic properties, based on a Kelvin-Voigt model, to the major constituents, glomeruli, interstitia, tubules, and fluid and simulated the wave propagation through tissue with no disease, inflammation, interstitial fibrosis, and tubular atrophy. The resulting in silico wave motion in the time- and frequency-domains was characterized to compare the in silico and in vivo mechanical properties. We also attempted modeling the effects of perfusion by modifying the constituents’ viscoelastic properties. We found the most differentiation for shear elasticity, shear viscosity, and phase velocity dispersion in the inflammation patients. When accounting for perfusion we observed increases in shear wave group velocity, shear viscosity, and dispersion, bringing the results from in silico models in closer agreement with in vivo results. These results are encouraging and demonstrate first steps of simulating the shear wave propagation based on histological models.