Noninvasive wall shear stress measurements in human carotid artery using echo particle image velocimetry: Initial clinical studies

Wall shear stress (WSS) has been shown to be important to endothelial cell function and gene expression. Previous studies have shown that fluid dynamics might be closely related to the initialization of atherosclerotic plaques which preferentially originate in areas of disturbed flow in human vessels, where WSS is low or oscillatory. We recently developed a novel ultrasound-based technique, termed echo particle image velocimetry (echo PIV), by which the multi-component hemodynamic information in human cardiovascular system could be assessed. In this paper, we show that echo PIV was successfully employed to measure hemodynamic information in the right common carotid artery (rCCA) of ten healthy volunteers and that the values show good agreement with phase-contrast magnetic resonance imaging (PC-MRI) measurements with mean absolute differences (mean±SD) of 10.0%±9.8%, 10.1%±8.8% and 17.0%±15.3% for velocity, flow rate and WSS, respectively. In particular, the mean WSS (dynes/cm^2) in rCCA of ten volunteers was found to be 9.2±2.0 by echo PIV, and 8.0±1.4 by PC-MRI, both in agreement with published data. We further showed that calculating WSS by either peak/mean velocity or flow rate together with arterial diameter was invalid for in-vivo measurements due to invalidity of assuming parabolic velocity profile in carotid artery. We found that the peak velocity across radial direction in rCCA was about 1.6 times of the mean velocity, not 2 times as it should be in parabolic distribution. In conclusion, echo PIV demonstrated several advantages over traditional techniques in terms of both temporal and spatial resolution when measuring WSS in human vessels.