Abstract
Blood flow velocity and wall shear stress (WSS) influence and are influenced by vascular disease. Their measurement is consequently useful in the laboratory and clinic. Contrast-enhanced ultrasound image velocimetry (UIV) can estimate them accurately but the need to inject contrast agents limits utility. Singular value decomposition and high-frame-rate imaging may render contrast agents dispensable. Here we determined whether contrast agent-free UIV can measure flow and WSS. In simulation, accurate measurements were achieved with a signal-to-noise ratio of 13.5 dB or higher. Signal intensity in the rabbit aorta increased monotonically with mechanical index; it was lowest during stagnant flow and uneven across the vessel. In vivo measurements with contrast-free and contrast-enhanced UIV differed by 4.4% and 1.9% for velocity magnitude and angle and by 9.47% for WSS. Bland–Altman analysis of waveforms revealed good agreement between contrast-free and contrast-enhanced UIV. In five rabbits, the root-mean-square errors were as low as 0.022 m/s (0.81%) and 0.11 Pa (1.7%). This study indicates that with an optimised protocol, UIV can assess flow and WSS without contrast agents. Unlike contrast-enhanced UIV, contrast-free UIV could be routinely employed.
Highlights
Cerebrovascular and coronary heart disease can be triggered by and cause local disturbances in blood flow and haemodynamic wall shear stress (WSS, Tw) (Cecchi et al 2011)
Flow simulation To assess the effect of scatter properties on the accuracy of blood flow and WSS measurement, we modeled flow in the abdominal aorta of a New Zealand White (NZW) rabbit as Womersley flow with alterations in scatter amplitude, radial intensity distribution and scatter density
Radial variation in intensity was used to mimic the dependence of aggregation and of scattering on shear rate
Summary
Cerebrovascular and coronary heart disease can be triggered by and cause local disturbances in blood flow and haemodynamic wall shear stress (WSS, Tw) (Cecchi et al 2011). High WSS likely plays a crucial role in aortic dilatation (RodrıguezPalomares et al 2018) because regions exposed to high WSS exhibit dysregulation of the extracellular matrix and medial elastin degradation. Intracranial aneurysms are more vulnerable to rupture when exposed to low WSS (Zhou et al 2017). Identifying regions of abnormal flow with high or low WSS could lead to a WSS is the product of blood viscosity m and the first-order spatial derivative of velocity (shear rate) near the wall. Large dynamic range of detectable velocities and precise localization and tracking of the luminal boundary are required to accurately estimate the shear rate. The rheology can be complex, but Newtonian rheology is often assumed for large arteries so that WSS reduces to
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