Role of ultrasonic velocity estimation errors in assessing inflammatory response and vascular risk

Ultrasound has great potential for accurate estimation of velocity gradients near blood vessel walls for measuring wall shear stress (WSS) at high spatial resolution. Arterial sites of low and oscillating WSS promote inflammatory responses that increase the risk of developing atherosclerotic plaques. We implemented broadband coded excitation techniques on a commercial scanner to estimate WSS with high spatial and temporal resolution. Ultrasonic measurement errors were quantified over the shear range of 0.3-1.5 Pa, where errors slowly increase with WSS. Expression of cellular adhesion molecules (CAM) associated with atherosclerosis development was also investigated over a similar range of shear stress (0-1.6 Pa) to study the impact of registering shear-mediated CAM expression to incorrect WSS estimates. Ultrasonic measurement errors generated the largest uncertainties in assessing endothelial cell function in the shear range where the sensitivity of CAM expression was high. For VCAM-1, errors near WSS = 0.4 Pa were most important, while for E-selectin errors near WSS = 0.8 Pa were greatest. These data help to guide the design of new ultrasonic techniques for monitoring vascular shear stress in patients particularly at the potential sites of early atherogenesis.