Angle-Independent, Contrast-Free Functional Ultrasound Based on Speckle Decorrelation

Present functional ultrasound methods have limitations: color Doppler imaging blood flow and its direction but is susceptible to noise, varies with angle and is inaccurate if opposite flows exist in the same voxel. Power Doppler imaging is less sensitive to angle but varies with other factors that affect amplitude. Microbubble tracking-based ultrasound localization microscopy provides blood flow images with super resolution but relies on contrast agents and requires extended data acquisition time. A new ultrasound velocimetry (vUS) approach based on ultrasound field speckle decorrelation analysis is presented which is quantitative, angle independent, does not require contrast agents, accounts for opposite flows, and is robust in the presence of noise and operates quickly. We have implemented vUS with ultrafast ultrasound coherence plane wave compounding data acquisition and compared the methods on controlled flow phantoms and awake mice. Axial and transverse flow velocities from vUS compare favorably with ultrasound localization microscopy but without microbubbles, and the frame rate can realize up to 5 frames/s with an ordinary spatial resolution of $\sim 100\ \mu \mathrm{m}$ . vUS cerebral blood flow velocity changes in a mouse brain were obtained in response to a 5 s whisker stimulation.