Having prior knowledge about changes in arterial wall material properties (stiffening of the wall) in patients could help doctors predict such a commonly wide-spread disease like atherosclerosis and, as a consequence, prevent other health- and life-threatening conditions: brain stroke or myocardial infarction. Nowadays, there is still lack of a technique in common clinical practice, that could estimate arterial wall stiffness directly and accurately, and being able to detect small, early-stage disease development.

Supersonic shear wave imaging technique in arterial applications could fill this niche. The principal concept behind the technique is straightforward and smart: you apply a small force onto the arterial wall by focused ultrasound. This force, called acoustic radiation force, creates secondary waves, called shear waves, which propagate with a certain speed. By measuring their propagation speed, we can deduce the material properties of the arterial wall (i.e. stiffness).

Unfortunately, in practice it is more complicated than that: due to the small thickness of arterial walls, such induced shear waves behave as guided waves, making the conversion between their speed and arterial elasticity complex. To be able to correctly predict arterial stiffness by using this technique, we have to improve our understanding of the nature of these waves in arterial wall settings.

My PhD focuses on series of controlled experiments on phantom materials (see figure below) and ex-vivo equine aortic tissues using both supersonic shear wave imaging technique and a mechanical testing machine to measure tissue stiffness. Afterwards, I try to model the same experiment numerically and gain more insight into the propagation of the resulted shear waves and the dependence of the shear wave speed on the arterial geometry and intrinsic material properties: anisotropy and non-linearity.

Figure: Experimental setup with a tubular PVA phantom fixed between clamps and pressurized with a water column, an ultrasound probe fixated above to perform supersonic shear wave imaging. 

You can find more about my experiments and general background information in the following articles:

[1] Shcherbakova, D., Papadacci, C., Swillens, A., Caenen, A., De Bock, S., Saey, V., Chiers, K., et al. (2014). Supersonic shear wave imaging to assess arterial nonlinear behavior and anisotropy: proof of principle via ex vivo testing of the horse aorta. Advances In Mechanical Engineering, 1–12.

[2] Sarvazyan, A.P., Skovoroda, A.R., Emelianov, S.Y., Fowlkes, J. B., Pipe, J. G., Adler, R.S., Buxton, R.B., Carson, P.L. (1995) Biophysical bases of elasticity imaging. Acoustical Imaging 21, 223–240.

[3] Sarvazyan, A.P., Rudenko, O. V., Swanson, S. D., Fowlkes, J. B., Emelianov, S. Y. (1998) Shear wave elasticity imaging: a new ultrasonic technology of medical diagnostics. Ultrasound Med & Biol 9, 1419-1435.

[4] Couade, M., Pernot, M., Prada, C., Messas, E., Emmerich, J., Bruneval, P., Criton, A., Fink,M., Mickael, T. (2010). Quantitative assessment of arterial wall biomechanical properties using shear wave imaging. Ultrasound Med & Biol 36, 1662 – 1676.

Written by Darya Shcherbakova.