Laminar fMRI using magnetization transfer contrast at 7 T.

Area of Science:

• Neuroimaging
• Functional Magnetic Resonance Imaging (fMRI)
• Biophysics

Background:

• Conventional blood-oxygenation-level-dependent (BOLD) fMRI suffers from limited spatial specificity due to extravascular signal dephasing near draining veins.
• Cerebral blood volume (CBV) and cerebral blood flow contrasts offer better laminar specificity but have lower sensitivity and temporal efficiency.

Purpose of the Study:

• To evaluate a specific-absorption-rate-efficient magnetization-transfer contrast (MTC) fMRI as a complementary method for laminar fMRI.
• To assess MTC fMRI's ability to provide improved spatial specificity while maintaining functional sensitivity and acquisition efficiency.

Main Methods:

• Utilized on-resonance, small-flip-angle binomial pulse trains to create MTC.
• Developed an MTC fMRI sequence that selectively attenuates extravascular signals, enhancing intravascular blood signal for CBV-weighted contrast.
• Evaluated MTC fMRI at 7 Tesla in the human primary motor (M1) and visual (V1) cortices.

Main Results:

• MTC fMRI demonstrated a double-peak laminar profile in M1, with signal peaks in superficial and deep cortical layers.
• In V1, MTC fMRI revealed an activation shift towards middle cortical depths and faster signal decay towards the surface compared to BOLD fMRI.
• The MTC approach successfully generated a CBV-weighted contrast with retained functional sensitivity.

Conclusions:

• MTC fMRI presents a practical solution for enhancing spatial specificity in laminar fMRI.
• This method achieves a favorable balance between spatial specificity, functional sensitivity, and acquisition efficiency.
• MTC fMRI is a promising complementary technique for non-invasive, depth-dependent functional organization studies.