THE INTRAVASCULAR CONTRIBUTION TO FMRI SIGNAL CHANGE - MONTE-CARLO MODELING AND DIFFUSION-WEIGHTED STUDIES IN-VIVO

Understanding the relationship between fMRI signal changes and activat ed cortex is paramount to successful mapping of neuronal activity. To this end, the relative extravascular and intravascular contribution to fMRI signal change from capillaries (localized), venules (less locali zed) and macrovessels (remote, draining veins) must be determined, In this work, the authors assessed both the extravascular and intravascul ar contribution to blood oxygenation level-dependent gradient echo sig nal change at 1.5 T by using a Monte Carlo model for susceptibility-ba sed contrast in conjunction with a physiological model for neuronal ac tivation-induced changes in oxygenation and vascular volume fraction, The authors compared our Model results with experimental fMRI signal c hanges with and without velocity sensitization via bipolar gradients t o null the intravascular signal. The model and experimental results ar e in agreement and suggest that the intravascular spins account for th e majority of fMRI signal change on T-2-weighted images at 1.5 T.