Purpose Flow instability has been shown to contribute to the risk of future cardiovascular and cerebrovascular events. Nonetheless, it is challenging to noninvasively detect and identify flow instability in blood vessels. Here, we present a new framework called Doppler ultrasound bandwidth imaging ( DUBI ) that uses high‐frame‐rate ultrasound and Doppler bandwidth analysis principles to assess flow instability within an image view. Methods Doppler ultrasound bandwidth imaging seeks to estimate the instantaneous Doppler bandwidth based on autoregressive modeling at every pixel position of data frames acquired from high‐frame‐rate plane wave pulsing. This new framework is founded upon the principle that flow instability naturally gives rise to a wide range of flow velocities over a sample volume, and such velocity range in turn yields a larger Doppler bandwidth estimate. The ability for DUBI to map unstable flow was first tested over a range of fluid flow conditions (ranging from laminar to turbulent) with a nozzle‐flow phantom. As a further demonstration, DUBI was applied to assess flow instability in healthy and stenosed carotid bifurcation phantoms. Results Nozzle‐flow phantom results showed that DUBI can effectively detect and visualize the difference in Doppler bandwidth magnitude (increased from 2.1 to 5.2 kH z) at stable and unstable flow regions in an image view. Receiver operating characteristic analysis also showed that DUBI can achieve optimal sensitivity and specificity of 0.72 and 0.83, respectively. In the carotid phantom experiments, differences were observed in the spatiotemporal dynamics of Doppler bandwidth over a cardiac cycle. Specifically, as the degree of stenosis increased (from 50% to 75%), DUBI showed an increase in Doppler bandwidth magnitude from 1.4 kH z in the healthy bifurcation to 7.7 kH z at the jet tail located downstream from a 75% stenosis site, thereby indicating flow perturbation in the stenosed bifurcations. Conclusion DUBI can detect unstable flow. This new technique can provide useful hemodynamic information that may aid clinical diagnosis of atherosclerosis.

Unstable flow plays an important role in the initiation and progression of atherosclerosis. Yet, mapping flow instability in arteries is challenging because such event is dynamic over both space and time. In this work, we present a new framework called Doppler ultrasound bandwidth imaging (DUBI) that makes use of high-frame-rate plane wave excitation and Doppler bandwidth analysis principles to identify unstable flow regions within an image view. DUBI works by performing autoregressive modeling at every pixel position to estimate the instantaneous Doppler bandwidth, which in principle is broadened by the wider range of velocities attributed to the emergence of unstable flow. DUBI’s performance in mapping unstable flow was tested with laminar and turbulent flow conditions in a nozzle-flow phantom. Results showed that DUBI was able to quantify the difference in Doppler bandwidth magnitude (increased from 2.1 to 5.2 kHz) as the flow condition changed from laminar to turbulent. Also, DUBI was found to be able to identify and map the unstable flow region with the image view, outperforming conventional Doppler variance imaging. This observation was substantiated by receiver operating characteristic analysis, in which DUBI achieved a sensitivity of 0.72 and specificity of 0.83 (vs 0.66 and 0.68, respectively, for conventional Doppler variance imaging). We anticipate that DUBI can be applied in vivo to obtain useful information for clinical diagnosis of atherosclerosis.