Quantifying elasticity and viscosity of urethane rubber using Shearwave Dispersion Ultrasound Vibrometry (SDUV) and the embedded sphere method

Diastolic dysfunction is the inability of the left ventricle (LV) to supply sufficient stroke volumes under physiological conditions and is often accompanied by LV myocardial stiffening. Our group has been investigating the use of Shearwave Dispersion Ultrasound Vibrometry (SDUV), a noninvasive ultrasound based method for quantifying viscoelasticity of the soft tissues. The primary motive of this study is the design and testing of a viscoelastic material suitable for validation of the Lamb wave model in the heart. Here, we report the results of quantifying viscoelasticity of urethane rubber samples using SDUV and our embedded sphere method. A urethane plate was embedded in gelatin inside a plastic container and mounted on a stand inside a water tank. A mechanical actuator was used to induce harmonic waves in the frequency range 40 - 500 Hz. A pulse-echo transducer was used to detect the motion at multiple points away from the excitation point. Linear regression of the phase data provided estimates of shear wave speed at each frequency (shear wave dispersion). An antisymmetric Lamb wave model was fitted to the dispersion data to estimate elasticity and viscosity of the material. ABAQUS finite element model (FEM) 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. The FEM dispersion data were in excellent agreement with the theoretical predictions. Elasticity and viscosity of the urethane rubber were 39.8±1.3 kPa and 5.0±0.4 Pa s, using SDUV, and 42.5±2.8 kPa and 5.2±0.4 Pa s, using the embedded sphere method.