Rapid Directional Ultrasound Super-Resolution Flow Imaging using Erythrocytes, Hankel Decomposition, and Optical Flow

A rapid, contrast-free method for ultrasound super-resolution vector flow imaging is introduced. The approach enhances the SURE-Hankel pipeline by integrating frequency-based directional separation, Hankel-matrix Singular Value Decomposition (HSVD), and localized optical flow estimation. A multi-stage process isolates overlapping erythrocyte signals based on their directional and spatiotemporal characteristics. Subsequently, optical flow is applied to the envelope of these separated modes for 2D flow vector estimation. The method’s validation was performed on an in vivo rat kidney (8.7 MHz center frequency, wavelength λ≈ 178 µm). For 1-second acquisitions, spatial resolution was improved to 40.8 µm from 57.5 µm using standard SURE. Flow direction accuracy, quantified against ULM velocimetry, resulted in a mean absolute Flow Angle Difference of 28.7° and a mean bias of 1.3°, successfully determining flow direction both axially and laterally. This technique enables accurate, non-invasive vector flow mapping of the microvasculature within acquisitions compatible with a single breath-hold.