Dynamic micro-elastography applied to the viscoelastic characterization of a mimicking artery and a porcine aorta

Because early signs of most cardiovascular diseases involve hardening of arteries, the development of non-invasive methods to provide in vivo assessment of mechanical properties of vessel walls could be of great importance in clinical practice. Most important limitations of methods proposed so far are the investigation of only the mean longitudinal wall elasticity parameters along a vessel segment in a restricted frequency range below 500 Hz. We propose to adapt the dynamic microelastography method to study the radial viscoelasticity of thin-walled cylindrical geometry phantoms. The technique firstly implies the generation of a low frequency (300-600 Hz) plane transient shear wave in the vascular phantom and the tracking of this wave with an ultrasound biomicroscope (Vevo 770, Visualsonics) providing in post-processing a very high frame rate (16000 images per second). An inverse problem was formulated as a least-square minimization between analytical simulations and experimental measurements to retrieve storage (G') and loss (G") moduli as functions of the shearing frequency. Result on a 3-mm wall mimicking artery permitted to validate the feasibility and the reliability of the inverse problem formulation. Then, G' and G" of a porcine aorta showed that both parameters are strongly dependant on frequency increasing, allowing to assume that such a biological tissue is mechanically governed by complex viscoelastic laws.