Geometric Dependence of Wave Velocity in Carotid Arteries: Phantom and Finite Element Study

Objective: The intrinsic elasticity and the structural stiffness of blood vessels are widely regarded as important biomarkers for prediction of cardiovascular disease risk, the leading cause of death worldwide. Ultrasound-based shear wave elastography (SWE) has been used to measure these properties in several clinical studies. However, the geometric properties of blood vessels complicate the relationship between wave speed and elasticity in blood vessels compared to bulk tissue. Here we quantify these effects with a semi-analytical finite element (SAFE) model and ultrasound experiments and discuss their implications for the vascular \u201cshear wave\u201d (better described as \u201cguided wave\u201d) elastography literature.Methods: A previously developed SAFE model was employed to simulate wave propagation after insonification with an acoustic radiation force (ARF) in 4,437 combinations of vascular geometry and elasticity. Group velocities were extracted and underwent processing analogous to what a SWE-equipped ultrasound scanner would perform to estimate Young\u2019s modulus (), and were compared to the true Young\u2019s modulus used in the simulation. Additionally, 23 polyvinyl alcohol cryogel tubes of different geometries and elasticities were constructed and underwent ARF-based SWE and reference inflation-based mechanical testing. Wave speeds were converted to Young\u2019s modulus using the same method as in the finite element study and were compared with the Young\u2019s modulus obtained from mechanical testing.Results: Both the SAFE simulations and PVA tube ultrasound experiments confirm the dependence of wave speed on vascular geometry which leads to a severe, geometry-dependent underestimation of Young\u2019s modulus if geometry is not considered.