Purpose: To evaluate the sensitivity of quantitative imaging biomarkers (QIBs) based on shear wave elasticity imaging (SWEI) to changes in cervical viscosity during pregnancy through finite-element simulations.
Methods: Shear wave particle displacements induced by acoustic radiations forces in standard-linear viscoelastic media with varying amounts of viscosity (6 - 60 Ps) were simulated with LS-DYNA (Livermore Software Technology Corp., Livermore, CA). Gaussian noise was added to displacements, with standard deviation being a multiple (k=0.01-0.1) of the maximum displacement. Two QIBs were extracted from displacement data: the ratio R of the group speed obtained from particle velocities and particle displacements, and the slope S of the phase velocity vs. frequency. Sensitivity was quantified by the contrast-to-noise ratio (CNR) with respect to the material with the lowest viscosity (6 Ps). Twenty realizations of the noisy displacement fields were simulated to obtain mean and standard deviations of the CNR
Results: In general, the CNR of both S and R increased with viscosity and decreased with noise, as expected. For high viscosities and low noise (k=0.01), the CNR of S is 5.5 times greater than that of R. However, as noise increases and viscosity decreases, the CNR of R becomes larger than that of S up to a factor of 1.9. The decrease in S CNR is due to bias caused by high-frequency noise in the estimation of the phase velocity slope.
Conclusion: Preliminary results indicate the potential of R and S as possible biomarkers of cervical remodeling, with parameter R being more sensitive than S in conditions of noisy shear wave displacement data, like those obtained from the relatively stiff cervix. We are currently investigating the use of noise filters to increase the CNR of R and S and applying these results to data from a non-human primate model of the pregnant cervix.
Funding Support, Disclosures, and Conflict of Interest: Supported by the NIH grant R01HD072077, UNAM-PAPIIT IA104518, UNAM-PAEP, and Proyectos de Investigacion del Instituto de Fisica