Introduction:
Shear Wave Elastography (SWE) is a recently developed noninvasive method for elastography assessment using ultrasound. The technique consists of sending an acoustic radiation force into the tissue that in turn generates an orthogonal low frequency propagating shear wave. The shear wave propagation speed, which is calculated from B-mode images, is correlated to the tissues mechanical properties. Currently, SWE is primarily used in breast and liver to detect tumors easily missed with normal B-mode ultrasound. SWE could potentially aid in the characterization of plaques in the carotid artery, which is critical for the prevention of ischemic stroke.
Methods:
Six polyvinyl alcohol (PVA) phantoms were created with soft and hard plaque mimicking inclusions. The plaques were excited with acoustic radiation force and the shear wave was measured using high speed B-mode imaging. The data was post-processed with a custom in-house algorithm fitting a model of a Lamb wave propagating through a plate to the shear wave dispersion curve, which allowed the shear modulus to be estimated. The results were validated by measuring the phantom plaque shear modulus with mechanical testing.
Results:
SWE measured a mean shear modulus of 6 ± 1 kPa and 106 ± 17 kPa versus 3 kPa and 95 kPa measured by mechanical testing in the soft and hard plaques respectively. The results show good agreement between the shear modulus measured with SWE and mechanical testing. In this study simplified homogenous phantom plaque models were examined in a static experimental setup with results validated by mechanical testing. Algorithm improvements for measurements in a dynamic environment are being developed for a future in vivo pilot study.
Conclusion:
The results show good agreement between the shear modulus measured with SWE and mechanical testing and indicate the possibility for an in vivo application.
Phase Aberration and Attenuation Effects on Acoustic Radiation Force-Based Shear Wave Generation