Estimation of Longitudinal Shear Strain in the Carotid Arterial Wall Using Ultrasound Radiofrequency Data

Abstract

The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. It is hypothesized that shear strain in the adventitia initiates and/or stimulates development of these plaques into rupture-prone, vulnerable plaques. Therefore, assessment of shear strain might yield a prognosis for the development of vulnerable plaques. In simulations and phantom experiments, longitudinal shear strain was estimated using RF and envelope-based methods and compared to the applied values. Additionally, longitudinal shear strain estimates in the adventitia of six healthy volunteers were determined. In both experiments, the variance of the RF-based estimates was significantly smaller than that of the envelope-based estimates (Wilcoxon, p<0.05). The periodicity of these estimates corresponded well with the cardiac cycle. The estimated values were found to be similar to previously published data. Furthermore, the signal-to-noise ratio of the shear strain estimate in the posterior wall based on RF-data was significantly higher (Wilcoxon, p 0<0.05) than that based on envelope-data. In conclusion, noninvasive ultrasound strain imaging using radiofrequency signals appeared to allow adequate estimation of longitudinal shear strain in the adventitial layer of the carotid artery wall.