A practical modification to a resting state fMRI protocol for improved characterization of cerebrovascular function

Area of Science:

• Neuroimaging
• Cardiovascular Physiology
• Biomedical Engineering

Background:

• Cerebrovascular reactivity (CVR) quantifies brain blood flow regulation in response to CO2 changes.
• CVR amplitude and timing (hemodynamic lag) offer insights into cerebrovascular health and fMRI noise.
• Current resting-state fMRI protocols may not fully capture CVR dynamics.

Purpose of the Study:

• To assess a modified resting-state fMRI protocol for improved cerebrovascular function characterization.
• To evaluate the impact of incorporating a brief breathing task on CVR and lag estimation.
• To demonstrate the clinical utility and feasibility of the enhanced protocol.

Main Methods:

• Healthy subjects (n=9) underwent resting-state fMRI with and without a 2-3 minute breathing task (hypercapnia/hypocapnia).
• Voxel-wise CVR and hemodynamic lag were modeled by optimizing the timing of the CO2 regressor.
• Analysis compared CVR and lag estimates between resting-state only and hybrid protocols.

Main Results:

• The hybrid protocol significantly increased the number of voxels with significant CO2-BOLD relationships.
• Incorporating a breathing task improved the confidence and plausibility of CVR and lag estimates.
• Optimization of CO2 regressor timing inherently increased gray matter CVR values and fit statistics.

Conclusions:

• A hybrid resting-state fMRI protocol with a brief breathing task enhances CVR and hemodynamic lag mapping.
• This method improves the characterization of cerebrovascular function and has clinical applications.
• The protocol shows promise for fMRI denoising, interpretation, and clinical settings, including pediatric populations.