Quantitative Hemodynamic Measurements in Cortical Vessels Using Functional Ultrasound Imaging

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Imaging

Background:

• Cerebral blood flow (CBF), volume (CBV), and red blood cell velocity (RBCv) are crucial for brain hemodynamics.
• Functional ultrasound imaging (fUS) offers high-resolution, real-time CBV measurement but struggles with RBCv and CBF in small cortical vessels.
• Vessel orientation and size pose challenges for precise RBCv and CBF measurements using standard fUS.

Purpose of the Study:

• To overcome limitations in measuring RBCv and CBF in small cortical vessels using fUS.
• To develop a directional flow filter compatible with standard fUS systems for RBCv measurement without contrast agents.
• To analyze changes in RBCv in cortical vessels during forepaw stimulation in rats.

Main Methods:

• Designed and implemented a directional flow filter for fUS to enable RBCv measurement in single vessels.
• Utilized a standard fUS system without contrast agents (e.g., microbubbles).
• Quantified RBCv changes in cortical vessels of adult rats during forepaw stimulation.

Main Results:

• Successfully measured RBCv in single cortical vessels, estimating approximately 650 vessels/cm³ in adult rats.
• Observed a significant increase in RBCv (median ~15%, max ~60%) in ~40 vessels within the primary somatosensory forelimb cortex during stimulation.
• Found higher RBCv in penetrating arterioles at the center compared to the periphery of the activated brain area.

Conclusions:

• The developed directional flow filter extends fUS capabilities for precise RBCv measurement in small brain vessels.
• This advancement facilitates a deeper understanding of neurovascular coupling at the brain-wide scale.
• The method offers a valuable tool for studying brain hemodynamics and functional hyperemia.