Measuring brain beats: Cardiac-aligned fast functional magnetic resonance imaging signals

Area of Science:

• Neuroimaging
• Fluid Dynamics
• Cardiovascular Physiology

Background:

• Brain health relies on intricate blood and cerebrospinal fluid (CSF) dynamics, synchronized with the cardiac cycle.
• Noninvasive magnetic resonance imaging (MRI) methods traditionally characterize these essential fluid movements.
• Recent advancements in fast MRI, particularly simultaneous multislice acquisition, enable quicker and more comprehensive assessments of cardiac-driven flow.

Purpose of the Study:

• To evaluate the efficacy of rapid, simultaneous multislice MRI techniques for assessing cardiac-driven blood and CSF flow dynamics.
• To investigate the temporal relationship between functional MRI (fMRI) signals and the cardiac pulse in various brain compartments.
• To explore the potential of these techniques for estimating intracranial impedance and diagnosing related diseases.

Main Methods:

• Utilized simultaneous multislice MRI for brief (3.5 min) scans on a 3T scanner in five subjects.
• Measured cardiac pulses using photoplethysmography (PPG) and acquired simultaneous fMRI data.
• Retrospectively aligned fMRI signals to the heartbeat, analyzing temporal signals in CSF and blood vessels.

Main Results:

• Achieved highly reliable cardiac-gated fMRI temporal signals in CSF and blood (R² > 50%) on a heartbeat timescale.
• Observed a distinct pattern in blood vessels: a local signal minimum post-systole.
• Identified a contrasting pattern in CSF spaces (ventricles, subarachnoid spaces): a local signal maximum post-systole.

Conclusions:

• Cardiac-gated fMRI, accelerated by simultaneous multislice techniques, reliably captures brain fluid dynamics.
• Distinct temporal fMRI signal patterns in blood and CSF post-systole offer insights into intracranial impedance.
• This approach holds promise for novel diagnostic tools in conditions affecting brain fluid dynamics.