Intracranial gradient-echo and spin-echo functional MR angiography in humans

Area of Science:

• Neuroimaging
• Functional Magnetic Resonance Imaging (fMRI)
• Vascular Physiology

Background:

• Blood oxygenation level-dependent (BOLD) contrast is a cornerstone of functional magnetic resonance imaging (fMRI).
• Gradient-echo (GRE) echo-planar imaging (EPI) is commonly used for BOLD fMRI.
• The precise origin of the BOLD signal, particularly the contribution of venous vasculature, remains an area of active investigation.

Purpose of the Study:

• To investigate the predominance of venous signal intensity in 1.5-T GRE fMRI of motor activity.
• To demonstrate the contribution of task-induced changes in venous flow velocity to the fMRI signal.

Main Methods:

• Healthy volunteers underwent fMRI of motor activity using conventional 2D GRE BOLD techniques.
• Image planes were positioned to specifically target responding veins.
• A second examination utilized 2D spin-echo (SE) techniques with axial orientation for comparison.
• Maximum intensity projection was used for processing hyperintense areas.

Main Results:

• Functional MR angiograms were successfully acquired using both GRE and SE techniques.
• The generation of SE functional MR angiograms confirmed the contribution of venous inflow effects.
• These findings indicate substantial venous contribution to signal intensity in conventional GRE BOLD fMRI.

Conclusions:

• Veins play a substantial role in the BOLD signal detected during fMRI of motor activity.
• Understanding venous contributions is crucial for accurate interpretation of fMRI data.
• Task-induced changes in venous flow velocity significantly impact fMRI signal intensity.