Simultaneous coherent-incoherent motion imaging in brain parenchyma.

Area of Science:

• Neuroimaging
• Biophysics
• Fluid Dynamics

Background:

• Ultra-slow fluid flow in the brain, such as neurofluids and glymphatic circulation, is crucial for waste clearance and overall brain health.
• Traditional MRI techniques struggle to accurately measure these slow, subtle movements.
• Advancements in MRI hardware, particularly ultra-high-performance gradient systems, offer new possibilities for high-resolution physiological measurements.

Purpose of the Study:

• To develop and validate a novel phase-sensitive diffusion tensor magnetic resonance imaging (MRI) sequence for ultra-slow flow quantification.
• To achieve unprecedented velocity resolution (< 20 μm s⁻¹) for neurofluid dynamics.
• To enable non-invasive, time-resolved mapping of brain fluid motion throughout the cardiac cycle.

Main Methods:

• Implementation of a phase-sensitive diffusion tensor MRI sequence with optimized pulse timing.
• Integration of a pipeline for simultaneous reconstruction of magnitude and phase MRI data.
• Utilizing an ultra-high-performance brain MRI gradient system for enhanced sensitivity.
• Non-invasive data acquisition in human subjects, time-resolved over the cardiac cycle.

Main Results:

• Achieved velocity resolution of less than 20 μm s⁻¹, enabling detection of ultra-slow fluid motion.
• Successfully reconstructed both magnitude (diffusion metrics) and phase (velocity) data simultaneously.
• Generated coherent, time-resolved velocity maps of brain parenchyma in human subjects.
• Demonstrated the capability to non-invasively characterize diffusive fluid motion and coherent velocity.

Conclusions:

• The developed phase-sensitive MRI sequence and reconstruction pipeline are effective for quantifying ultra-slow neurofluid flow.
• High-performance brain MRI systems are essential for enabling such sensitive measurements.
• This technique holds significant promise for advancing the understanding of glymphatic circulation and neurofluid dynamics in health and disease.