Mapping Microvascular Flow via Radon Transform Ultrasound: Technical Advances and Pilot Application

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Ultrasound Technology

Background:

• Microvascular dysfunction is a key indicator in many diseases.
• Noninvasive methods for visualizing and quantifying abnormal microcirculation are limited.
• Accurate assessment of microcirculatory patterns is crucial for disease diagnosis and management.

Purpose of the Study:

• To develop a contrast-free ultrasound method (R-Flow) for in vivo microvascular flow vector mapping.
• To establish R-Flow-derived metrics for noninvasive quantification of microcirculatory patterns, particularly in liver cirrhosis.
• To assess the translational feasibility and diagnostic potential of R-Flow in human liver applications.

Main Methods:

• R-Flow utilizes the Radon transform to analyze red blood cell dynamics from ultrasound flow signals.
• Reconstruction of microvascular-scale velocity vectors from spatiotemporal ultrasound data.
• Derivation of direction-aware indices to characterize flow distribution and heterogeneity.

Main Results:

• R-Flow demonstrated robust velocity estimation (1-60 mm/s) validated in simulations, phantoms, and in vivo studies.
• High-sensitivity microvascular flow vector mapping of the human liver showed strong agreement with reference methods (r > 0.9).
• In a rat model of liver cirrhosis, R-Flow indices revealed a shift from healthy multipath perfusion to a directionally biased pattern, correlating with pathological indicators.

Conclusions:

• R-Flow provides noninvasive, contrast-free mapping of microvascular blood flow velocity.
• The technique offers a promising approach for high-resolution assessment of microvascular flow characteristics.
• R-Flow's direction-aware indices offer unique insights into hepatic flow dynamics and disease remodeling.