Wall Shear Imaging With Synthetic Aperture Universal Sequence: Preliminary In Vivo Precision Assessment in the Carotid Artery.

Wall shear stress (WSS) plays a crucial role in the initiation and progression of atherosclerosis. However, its noninvasive quantification remains challenging due to the limited spatiotemporal resolution and scalability of magnetic resonance imaging (MRI), as well as the limited precision (±30% error range) and image quality tradeoff of existing ultrasound-based approaches. This study presents an ultrasound-based wall shear imaging (WASHI) framework that simultaneously provides high-quality B-mode images and spatiotemporally resolved WSS maps, and evaluates its accuracy and precision. WASHI derives WSS directly from velocity gradients obtained using transverse oscillation vector flow imaging based on an interleaved synthetic aperture imaging sequence implemented on a Verasonics Vantage 256. Accuracy was assessed using a flow-rig setup under controlled conditions, and in vivo precision was evaluated in ten healthy volunteers through bilateral scans of the common carotid arteries (19 common carotid arteries (CCAs) in total). In the flow-rig experiments, WASHI produced consistent WSS estimates across 0° and 20° tilting angles with accuracy comparable to a velocity-based estimator (bias: -1 versus -3 mPa). In in vivo measurements, WASHI successfully tracked vessel wall motion over multiple cardiac cycles and resolved both spatial and temporal variations in WSS along both vessel walls. The median coefficient of variation (CV) across the 19 CCAs was 10.2%, demonstrating high measurement precision. Although this precision was slightly lower than that of the velocity-based estimator (CV: 6.2%), WASHI produced WSS magnitudes (2.7 and 2.3 Pa) that closely reflected the captured flow profile (2.9 and 2.4 Pa). In addition, the intrasubject variability of time-averaged WSS was the same across participants ( $p=0.45$ ), indicating reproducible performance. These results demonstrate the feasibility of WASHI for precise and reproducible WSS imaging, enabling future longitudinal studies and large-cohort investigations of vascular hemodynamics.