SWI Brain Vessel Change Coincident with fMRI Activation

Abstract

fMRI has been extensively used for the last ten years, however it is not fully understood what it really measures. To map brain function, fMRI is known to make use of a chain of physiological events, from neuronal activation to blood oxygenation, which gives rise to the BOLD signal.

The SWI (Susceptibility Weighted Imaging) sequence allows us to see the blood content of small venous vessels in the brain. This led us to look for the possibility of observing the changes in small vessels that occur during the activation of a particular brain area, by acquiring a set of images at rest and another set of images as the paradigm task is being performed. Subtracting the two sets it should be possible to see changes in oxygenation at the vessel level.

By comparing the SWI images with the fMRI activation maps obtained on the same paradigm we can look for coincidences of blood vessel changes with the fMRI activations and thus validate in images part of the accepted chain of physiological events occurring during neuronal activation.

Our 3D T1 images, functional images and SWI images were all obtained on the same axial locations so that we could compare them directly. The data obtained with SWI, BOLD activation and 3D FSPGR images for the same volunteers on the same axial plane, showed very good spatial correlation between the relevant eloquent areas. After subtraction the SWI image only showed the changed vessels on the same location as the fMRI activation areas. These corresponded to the cortical areas expected for the paradigms used, with a very good spatial correlation between the three images.

Our data seems to show that it is possible to see the vessel changes that occur during neuronal activation and correlate its localisation with the BOLD activation area.