Velocity Spectrum Imaging Using Velocity Encoding Preparation Pulses.

Area of Science:

• Medical Imaging
• Fluid Dynamics
• Neuroscience

Background:

• Accurate measurement of fluid velocity in biological tissues is crucial for understanding physiological processes.
• Current methods often require contrast agents or are invasive.
• Magnetic Resonance Imaging (MRI) offers a non-invasive imaging modality with potential for quantitative flow assessment.

Purpose of the Study:

• To introduce and validate a novel, non-invasive MRI technique for measuring the velocity distribution of water within individual voxels.
• To encode velocity information using motion-sensitizing gradients with a changing first moment.
• To enable contrast-free assessment of fluid dynamics in vivo.

Main Methods:

• Acquisition of a series of MRI images preceded by velocity-encoding preparatory radiofrequency (RF) pulses.
• Utilizing Fourier transforms for decoding the velocity distribution from the acquired image data.
• Demonstration on a flow phantom with known characteristics and on the brains of five human participants.

Main Results:

• Phantom velocity measurements aligned with theoretical predictions.
• Human brain scans revealed distinct anatomical features associated with different velocity ranges.
• The majority of observed spins were in lower velocity bands, with clear identification of cerebrospinal fluid (CSF) movement.

Conclusions:

• Velocity Spectrum Imaging (VSI) shows significant potential for studying in vivo fluid movement without contrast agents.
• VSI can serve as a tool for validating computational fluid dynamics (CFD) models and investigating the glymphatic system's role in neurodegeneration.
• Further research is needed to enhance sensitivity for ultra-low velocity measurements in perivascular spaces.