This study examined the BOLD signal changes in primary visual cortex as a function of luminous contrast at 1.5T in 4 normals and 2 patients with multiple sclerosis (MS) disease. Echo planar T2* weighted BOLD imaging experiments were performedusing a 1.5T Imager. Ten axial slices through the calcarine fissure were obtained. The imaging series consisted of alternations between a 20-second epoch of dark screen (rest) and a 20-second epoch of a flickering checkerboard (activation) repeated 6times. Each imaging series utilized a stepwise, graded increase of eight different luminance contrast levels. A paired t-test was used to compare the control condition with each activation condition. The data shows a linear trend in the number of fMRIactivated voxels within the visual cortex with increasing luminous contrast in normals and MS patients. This study demonstrates quantifiable changes in BOLD signal and a linear increase in activated voxels within the primary visual cortex with increasingluminous contrast.
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