Functional mapping of the human visual cortex at 4 and 1.5 tesla using deoxygenation contrast EPI.
Turner R., Jezzard P., Wen H., Kwong KK., Le Bihan D., Zeffiro T., Balaban RS.
The effects of photic stimulation on the visual cortex of human brain were studied by means of gradient-echo echo-planar imaging (EPI). Whole-body 4 and 1.5 T MRI systems, equipped with a small z axis head gradient coil, were used. Variations of image intensity of up to 28% at 4 T, and up to 7% at 1.5 T, were observed in primary visual cortex, corresponding to an increase of blood oxygenation in regions of increased neural activity. The larger effects at 4 T are due to the increased importance of the susceptibility difference between deoxygenated and oxygenated blood at high fields.