Viscoelastic response (VisR) imaging for assessment of viscoelasticity in voigt materials

Viscoelastic response (VisR) imaging is presented as a new acoustic radiation force (ARF)-based elastographic imaging method. Exploiting the Voigt model, VisR imaging estimates displacement in only the ARF region of excitation from one or two successive ARF impulses to estimate τσ, the relaxation time for constant stress. Double-push VisR τσ estimates were not statistically significantly different (p < 0.02) from those of shearwave dispersion ultrasound vibrometry (SDUV) or monitored steady-state excitation recovery (MSSER) ultrasound in six homogeneous viscoelastic tissue mimicking phantoms with elastic moduli ranging from 3.92 to 15.34 kPa and coefficients of viscosity ranging from 0.87 to 14.06 Pa·s. In two-dimensional imaging, double-push VisR τσ images discriminated a viscous spherical inclusion in a structured phantom with higher CNR over a larger axial range than single-push VisR or conventional acoustic radiation force impulse (ARFI) ultrasound. Finally, 2-D in vivo double-push VisR images in normal canine semitendinosus muscle were compared with spatially matched histochemistry to corroborate lower double-push VisR τσ values in highly collagenated connective tissue than in muscle, suggesting double-push VisR’s in vivo relevance to diagnostic imaging, particularly in muscle. The key advantages and disadvantages to VisR, including lack of compensation for inertial terms, are discussed

On the Quantitative Potential of Viscoelastic Response (VisR) Ultrasound Using the One-Dimensional Mass-Spring-Damper Model

Viscoelastic Response (VisR) ultrasound is an acoustic radiation force (ARF)-based imaging method that fits induced displacements to a one-dimensional (1D) mass-spring-damper (MSD) model to estimate the ratio of viscous to elastic moduli, τ, in viscoelastic materials. Error in VisR τ estimation arises from inertia and acoustic displacement underestimation. These error sources are herein evaluated using finite element method (FEM) simulations, error correction methods are developed, and corrected VisR τ estimates are compared to true simulated τ values to assess VisR’s relevance to quantifying viscoelasticity. In regards to inertia, adding a mass term in series with the Voigt model, to achieve the MSD model, accounts for inertia due to tissue mass when ideal point force excitations are used. However, when volumetric ARF excitations are applied, the induced complex system inertia is not described by the single-degree-of-freedom MSD model, causing VisR to overestimate τ. Regarding acoustic displacement underestimation, associated deformation of ARF-induced displacement profiles further distorts VisR τ estimates. However, median error in VisR τ is reduced to approximately −10% using empirically derived error correction functions applied to simulated viscoelastic materials with viscous and elastic properties representative of tissue. The feasibility of corrected VisR imaging is then demonstrated in vivo in the rectus femoris muscle of an adult with no known neuromuscular disorders. These results suggest VisR’s potential relevance to quantifying viscoelastic properties clinically

Viscoelastic response (VisR) imaging for assessment of viscoelasticity in voigt materials

Viscoelastic response (VisR) imaging is presented as a new acoustic radiation force (ARF)-based elastographic imaging method. Exploiting the Voigt model, VisR imaging estimates displacement in only the ARF region of excitation from one or two successive ARF impulses to estimate τ(σ), the relaxation time for constant stress. Double-push VisR τ(σ) estimates were not statistically significantly different (p < 0.02) from those of shearwave dispersion ultrasound vibrometry (SDUV) or monitored steady-state excitation recovery (MSSER) ultrasound in six homogeneous viscoelastic tissue mimicking phantoms with elastic moduli ranging from 3.92 to 15.34 kPa and coefficients of viscosity ranging from 0.87 to 14.06 Pa·s. In two-dimensional imaging, double-push VisR τ(σ) images discriminated a viscous spherical inclusion in a structured phantom with higher CNR over a larger axial range than single-push VisR or conventional acoustic radiation force impulse (ARFI) ultrasound. Finally, 2-D in vivo double-push VisR images in normal canine semitendinosus muscle were compared with spatially matched histochemistry to corroborate lower double-push VisR τ(σ) values in highly collagenated connective tissue than in muscle, suggesting double-push VisR’s in vivo relevance to diagnostic imaging, particularly in muscle. The key advantages and disadvantages to VisR, including lack of compensation for inertial terms, are discussed

On the Quantitative Potential of Viscoelastic Response (VisR) Ultrasound Using the One-Dimensional Mass-Spring-Damper Model

Viscoelastic Response (VisR) ultrasound is an acoustic radiation force (ARF)-based imaging method that fits induced displacements to a one-dimensional (1D) mass-spring-damper (MSD) model to estimate the ratio of viscous to elastic moduli, τ, in viscoelastic materials. Error in VisR τ estimation arises from inertia and acoustic displacement underestimation. These error sources are herein evaluated using finite element method (FEM) simulations, error correction methods are developed, and corrected VisR τ estimates are compared to true simulated τ values to assess VisR’s relevance to quantifying viscoelasticity. In regards to inertia, adding a mass term in series with the Voigt model, to achieve the MSD model, accounts for inertia due to tissue mass when ideal point force excitations are used. However, when volumetric ARF excitations are applied, the induced complex system inertia is not described by the single-degree-of-freedom MSD model, causing VisR to overestimate τ. Regarding acoustic displacement underestimation, associated deformation of ARF-induced displacement profiles further distorts VisR τ estimates. However, median error in VisR τ is reduced to approximately −10% using empirically derived error correction functions applied to simulated viscoelastic materials with viscous and elastic properties representative of tissue. The feasibility of corrected VisR imaging is then demonstrated in vivo in the rectus femoris muscle of an adult with no known neuromuscular disorders. These results suggest VisR’s potential relevance to quantifying viscoelastic properties clinically