4D Blood Flow and Wall Shear Stress measured using Volumetric Ultrasound Image Velocimetry

The ability to identify regions of abnormal flow and haemodynamic wall shear stress (WSS) plays a crucial role in understanding the underlying cause of a wide range of cardiovascular disease (CVD). However, quantitative assessment of WSS in vivo is difficult to perform. Ultrasound vector flow imaging in two dimensions is limited to measuring only two components of the flow, while speckle decorrelation methods measure only a single cross-section. Hence, WSS is either obtained through reductionist simulation which relies on simplifying assumptions or with phase contrast magnetic resonance imaging, which is expensive and suffers from a low spatiotemporal resolution. Here we demonstrate the potential of volumetric ultrasound image velocimetry (VUIV) to accurately measure spatiotemporally varying 3D blood flow and WSS in vitro and in vivo. Measurements were conducted in a straight vessel and carotid bifurcation phantom, and in the abdominal aorta of New Zealand White rabbits. In the straight vessel, flow rate/WSS error was 2.4%/3.5%. Steady and pulsatile flow in the carotid bifurcation were in agreement with simulation. In the abdominal aorta, waveform and distribution of velocity and WSS match literature values. Centerline velocity from VUIV and 2D UIV highly correlate (ρ=0.99), which illustrates the potential of VUIV to help understand the underlying causes of CVD.