Non-invasive assessment of shear strain in the carotid arterial wall based on ultrasound radiofrequency data

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. It has been hypothesized that the shear strain, induced in the adventitial layer by the pulsating pressure wave and blood flow, initiates and/or stimulates the development of such a plaque into a rupture-prone, vulnerable plaque. The aim of this paper was to experimentally test and validate methods to estimate longitudinal shear strain in arterial vessel walls and to investigate the feasibility of in vivo application. In simulations and in phantoms rf ultrasound data was used to estimate local longitudinal displacements and shear strain. The estimated shear strains were compared with the applied values. Additionally, rf-based estimates of longitudinal shear strain in the adventitia of the carotid artery wall were obtained in a healthy volunteer. In the simulations and phantom experiments, the estimates of longitudinal displacement and shear strain were linearly related to the applied displacement and shear strain (Spearman´s rho = 0.879 - 1.00, p < .05). The shear strain estimates in the in vivo experiments were found to be reproducible and the periodicity corresponded well with the cardiac cycle. Noninvasive ultrasound radiofrequency signals appeared to represent an adequate base for measurement of longitudinal shear strain in the adventitia layer of the carotid artery wall.