Spatio-Temporal Flow and Wall Shear Stress Mapping Based on Incoherent Ensemble-Correlation of Ultrafast Contrast Enhanced Ultrasound Images

Abstract

In this study, a technique for high-frame-rate ultrasound imaging velocimetry (UIV) is extended first to provide more robust quantitative flow velocity mapping using ensemble correlation of images without coherent compounding, and second to generate spatio-temporal wall shear stress (WSS) distribution. A simulation model, which couples the ultrasound simulator with analytical flow solution, was implemented to evaluate its accuracy. It is shown that the proposed approach can reduce errors in velocity estimation by up to 10-fold in comparison with the coherent correlation approach. Mean errors (ME) of 3.2% and 8.6% were estimated under a steady flow condition, while 3.0% and 10.6% were found under a pulsatile condition for the velocity and wall shear rate (WSR) measurement, respectively. Appropriate filter parameters were selected to constrain the velocity profiles before WSR estimations and the effects of incorrect wall tracking were quantified under a controlled environment. Although accurate wall tracking is found to be critical in WSR measurement (as a 200 µm deviation from the wall may yield up to a 60% error), this can be mitigated by HFR imaging (of up to 10 kHz) with contrast agents, which allow for improved differentiation of the wall-fluid boundaries. In vitro investigations on two carotid bifurcation phantoms, normal and diseased, were conducted, and their relative differences in terms of the flow patterns and WSR distribution were demonstrated. It is shown that high-frame-rate UIV technique can be a non-invasive tool to measure quantitatively the spatio-temporal velocity and WSS distribution.

Two-Stage Motion Correction for Super-Resolution Ultrasound Imaging in Human Lower Limb

“…Motion is an inherent part of in vivo imaging and US imaging methods based on multiple acquisitions suffer from motion artifacts even for images acquired at high frame rates with or without MBs [35]- [37]. For SR imaging, subwavelength motion correction methods are required to visualize microvascular structures and flow beyond the diffraction limit through localization of spatially isolated MBs.…”

Determining Haemodynamic Wall Shear Stress in the Rabbit Aorta In Vivo Using Contrast-Enhanced Ultrasound Image Velocimetry

“…The UIV algorithm used in this study has previously been published. 17,18 The basic principle is to calculate the displacement vector of all microbubbles in two consecutive B-Mode images separated by a known time delay in order to determine their velocity. Images were divided into interrogation windows (32 9 32 px) and a displacement vector for each patch was determined.…”

“…13,17,22,30,35 Physiological flow field velocity and hence shear rate can be resolved with high spatiotemporal resolution. 18,35 With known location of the vessel-wall boundary, obtainable with high temporal resolution from the same images, the distribution of WSS in the vessel can be derived. 8,9,34 Contrast agents greatly increase blood echogenicity and allow for better distinction between the vessel and the wall, facilitating WSS measurement.…”

A Systematic Review for the Design of In Vitro Flow Studies of the Carotid Artery Bifurcation

“…Seven out of 16 articles within the ultrasound category perform image velocimetry. Different acquisition protocols and post processing techniques are used: echo particle image velocimetry using contrast agent (echoPIV), 77 high-frame-rate ultrasound imaging velocimetry using speckle patterns, 36,37 Vector Projectile Imaging using multi-angle Doppler analysis, 72 transverse oscillation and directional beamforming for vector velocity estimation, 28 a biomechanical method that produces a map of displacement vectors, 45 and vector flow mapping using color Doppler images from a clinical system. 59 Doppler protocols are applied in seven articles.…”

“…77 There are several working fluids reported in the optical PIV studies, however, most studies use a glycerol-water mixture. Four of sixteen ultrasound studies use microbubbles as contrast material, both home-made 36,37,45 and commercial 77 (Table 3). Most other ultrasound articles use a blood mimicking fluid containing nylon particles.…”