Time-Resolved Wall Shear Rate Mapping Using High-Frame-Rate Ultrasound Imaging

Abstract

In atherosclerosis, low wall shear stress (WSS) is known to favor plaque development while high WSS increases plaque rupture risk. To improve plaque diagnostics, WSS monitoring is crucial. Here we propose wall shear imaging (WASHI), a non-invasive contrast-free framework that leverages high-frame-rate ultrasound to map wall shear rate (WSR) that relates to WSS by the blood viscosity coefficient. Our method measures WSR as the tangential flow velocity gradient along the arterial wall from flow vector field derived using multi-angle vector Doppler technique. To improve WSR estimation performance, WASHI semi-automatically tracks the wall position throughout the cardiac cycle. WASHI was first evaluated with an in vitro linear WSR gradient model; the estimated WSR was consistent with theoretical values (average error of 4.6 ± 12.4%). The framework was then tested on healthy and diseased carotid bifurcation models. In both scenarios, key spatiotemporal dynamics of WSR were noted: (i) Oscillating shear patterns were present in the carotid bulb and downstream to the ICA where retrograde flow occurs; (ii) High WSR was observed particularly in the diseased model where measured WSR peaked at 810 s -1 due to flow jet. We also showed that WASHI could consistently track arterial wall motion to map its WSR. Overall, WASHI enables high temporal resolution mapping of WSR that could facilitate investigations on causal effects between WSS and atherosclerosis.

Transrectal ultrasound vector projectile imaging for time‐resolved visualization of flow dynamics in the male urethra: A clinical pilot study

“…HiFRUS can acquire ultrasound images at a rate above 5000 frames per second (fps). This is more than 100 times the achievable frame rate of conventional ultrasound imaging, 12 showing its ability to visualize various body biological dynamics 13–18 . This high temporal resolvability has also enabled the simultaneous acquisition of color Doppler images with multiple beam angles and the estimation of flow vectors (flow speed and direction) at every pixel in each frame.…”

“…This is more than 100 times the achievable frame rate of conventional ultrasound imaging, 12 showing its ability to visualize various body biological dynamics. [13][14][15][16][17][18] This high temporal resolvability has also enabled the simultaneous acquisition of color Doppler images with multiple beam angles and the estimation of flow vectors (flow speed and direction) at every pixel in each frame. This technique, called vector projectile imaging (VPI), 19 has helped visualize time-resolved complex hemodynamics in the carotid, femoral, and thoracic arteries.…”