Lamb wave dispersion ultrasound vibrometry (LDUV) method for quantifying mechanical properties of viscoelastic solids

Abstract

Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of Shearwave Dispersion Ultrasound Vibrometry (SDUV), a noninvasive ultrasound based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb wave Dispersion Ultrasound Vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb waves and measure the dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb wave model was fitted to the wave speed dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb wave dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify mechanical properties of soft tissues with a plate-like geometry.

Noncontact depth-resolved micro-scale optical coherence elastography of the cornea

“…The dispersion of the Lamb wave propagation in a thin plate is related to the viscoelastic properties of the material. Recently, Lamb wave dispersion ultrasound micrometry [57] has been developed and demonstrated to be able to measure the shear elasticity and viscosity based on the fitting of the Lamb wave model to the experimental data. Thus, the experimental assessment of the Lamb wave dispersion in the cornea provides the potential possibility of simultaneously quantifying both the elasticity and the viscosity of the cornea.…”

“…This could significantly improve the accuracy of the corneal elasticity measurement due to taking the viscous behavior of the tissue into consideration, which is of great importance to advance the diagnosis and treatment of many corneal diseases. The existing low-frequency Lamb wave models are mainly developed for the flat plate-like samples in a fluid [57,63] and are not applicable for the cornea that is a curved thin plate. Also, in our experimental setup, the boundary condition for the cornea is different, as one side of the cornea is air (or can be considered as vacuum) and the other side is aqueous humor.…”

“…Specifically, the elastic wave propagation in cornea is partially guided by the top and bottom surfaces with consecutive reflections from these two boundaries, which shows the features of Lamb wave [55,56]. Two zero-order propagation modes usually exist for the Lamb wave in a thin plate under the low-frequency range (typically 0-2000 Hz): symmetric mode and antisymmetric mode [57]. In our experiment, as the direction of the air-puff delivery is set to be close to the corneal surface normal, the air-puff loading mainly generates the antisymmetric propagation mode.…”

Changes in cervical stiffness during pregnancy: Preliminary assessment with shear wave elasticity imaging in the rhesus macaque

“…Viscosity acts by increasing the absorption of the shear wave energy as well as by introducing dispersion (increase of the shear wave speed with frequency content). [32,33,34] Initial quantification of shear wave dispersion [35] suggests the presence of a viscous component in the NHP cervix, which increases with induced cervical remodeling. We expect that the incorporation of quantitative parameters related to viscosity will further increase the sensitivity to cervical remodeling.…”

Effect of Ultrafast Imaging on Shear Wave Visualization and Characterization: An Experimental and Computational Study in a Pediatric Ventricular Model

“…The shear modulus is then estimated by fitting a theoretical model in a least squares manner to the obtained dispersion curve. Neglecting the ventricular curvature [38] and PVA's viscoelasticity, and assuming that the main excited mode is the first antisymmetric mode (A0) [17], we minimized the difference between the theoretical A0 dispersion curve of a plate in water and the extracted dispersion characteristics over a frequency range spanning from 0.2 kHz up to maximally 2 kHz, dependent on the considered acquisition [37,39]. Only fits giving a standard deviation less than 0.6 kPa for the shear modulus estimate were considered.…”