Exploring the limits to quantitative elastography: supersonic shear imaging in stretched soft strips.

Abstract

Objective --- Shear wave elastography has enriched ultrasound medical imaging with quantitative tissue stiffness measurements. We aim to explore the limitations that persist related to viscoelasticity, guiding geometry or static deformation. Approach --- A nearly-incompressible soft elastomer strip is chosen to mimic the mechanical behavior of an elongated tissue. A supersonic shear wave scanner measures the propagation of shear waves within the strip. It provides a wide range of shear wave velocities, from 2 to 6~m/s, depending on the frequency, the static strain as well as the orientation of the strip. Main results --- To explain these different measurements, the guided wave effect is highlighted and analysed from the dispersion diagrams provided by the spatio-temporal Fourier transform of the raw data. The guided waves are then described using a material model that accounts for both the rheology and the hyperelastic behavior, and allows to extract the mechanical parameters of the sample. Significance --- To overcome some limitations of current elastography, we propose a theoretical framework which allows the simultaneous characterization of the viscoelastic and hyperelastic properties of soft tissues, paving the way for robust quantitative elastography of elongated tissues.