The spatial and temporal characteristics of the apparent-diffusion-coefficient-dependent fMRI signal changes during...

Area of Science:

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

Background:

• Blood oxygenation level dependent (BOLD) contrast in fMRI is widely used but can be spatially inaccurate due to venous signal contributions.
• Arterial spin labeled (ASL) techniques offer capillary sensitivity but are limited in temporal resolution and spatial coverage.
• Apparent diffusion coefficient (ADC) changes during brain activation present an alternative contrast mechanism with potential for improved localization.

Purpose of the Study:

• To investigate the temporal and spatial characteristics of ADC contrast in fMRI.
• To evaluate ADC contrast with arterial signal suppression and pixel-based analysis.
• To assess the potential of ADC contrast for exclusive capillary sensitivity.

Main Methods:

• Utilized isotropic diffusion weighting to measure apparent diffusion coefficient (ADC) changes during brain activation.
• Employed arterial signal suppression techniques to refine the ADC signal.
• Conducted both averaged global and pixel-based evaluations of ADC activation characteristics.

Main Results:

• ADC contrast demonstrates a spatial overlap with BOLD signals primarily in capillaries.
• ADC activation temporally precedes BOLD activation, indicating upstream arterial contributions.
• Pixel-based analysis revealed significant temporal heterogeneities within ADC activation, beyond global timing advances.

Conclusions:

• ADC contrast, particularly with arterial suppression, shows promise for more localized fMRI signal detection.
• The identified temporal heterogeneities in ADC activation provide insights into signal origins.
• Further characterization of ADC contrast could lead to fMRI techniques with exclusive capillary sensitivity, improving spatial accuracy.