American Journal of Neuroradiology 23:59-65, January 2002
© 2002 American Society of Neuroradiology
BRAIN
Quantitative Functional MR Imaging of the Visual Cortex at 1.5 T as a Function of Luminance Contrast in Healthy Volunteers and Patients with Multiple Sclerosis
a Department of Radiological Sciences, MCP Hahnemann University, Philadelphia, PA
b Department of Neurology, MCP Hahnemann University, Philadelphia, PA
c Department of Neurology, Thomas Jefferson University, School of Medicine, Philadelphia, PA
d School of Biomedical Engineering and Health Sciences, Drexel University, Philadelphia, PA
e Department of Neurology, Mount Sinai School of Medicine, New York, NY
f Tri-Service General Hospital and National Defense Medical Center, Taipei, Taiwan
g Department of Radiological Sciences, University of California, Irvine, CA
Address reprint requests to Scott H. Faro, MD, Department of Radiological Sciences, MCP Hahnemann University, 3300 Henry Ave., Philadelphia, PA 19129
BACKGROUND AND PURPOSE: In patients with multiple sclerosis (MS), a few preliminary functional MR (fMR) imaging studies of the visual cortex reveal information about magnitude differences between healthy individuals and patients with MS at only a single luminance level. We therefore investigated whether varying luminance contrast levels can help uncover subtle changes in fMR imaging characteristics of the visual cortex in healthy volunteers and patients with MS.
METHODS: Blood oxygenation level–dependent fMR imaging signal changes in the primary visual cortex were examined as a function of luminance contrast at 1.5 T in 10 healthy volunteers and nine patients with MS. Ten axial sections through the calcarine fissure were obtained with an echo-planar T2*-weighted imaging sequence (4000/54/1 [TR/TE/excitation]; field of view, 220 mm; voxel size, 1.72 x 1.72 x 5 mm). The imaging series consisted of an alternating 20-second rest epoch (black screen) with a 20-second activation epoch (flickering checkerboard) repeated six times. Each imaging series used a graded increase of eight luminance contrast levels. A paired t test between rest and activation images was used to analyze significant (P < .001) contiguous voxels in the region of interest (primary visual cortex).
RESULTS: A progressive increase in fMR imaging activation across all luminance contrast levels in healthy controls and patients with MS was shown. The patients with MS had a significantly lower magnitude in the number of fMR imaging activated voxels at all luminance contrast levels (P < .001). A statistically significant increase in fMR imaging activation (activation threshold) was seen at the second luminance contrast level in controls and at the seventh level in patients with MS.
CONCLUSION: Quantifiable changes in blood oxygenation level-dependent signal and a progressive increase in activated voxels within the primary visual cortex with increasing luminance contrast were demonstrated at 1.5 T in controls. The patients with MS showed a significant decrease in the number of activated voxels and an increase in activation threshold compared with healthy controls.
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