High-resolution echo-planar fMRI of human visual cortex at 3.0 tesla.

Known specialized properties of the human visual cortex have been used to investigate the role of spatial resolution on fMRI using blood oxygenation level dependent (BOLD) echo-planar MRI at 3.0 tesla. The magnitude of BOLD signal changes has been examined at low (3.1 x 3.1 x 3.0 mm3) and high (0.8 x 1.6 x 3.0 mm3) resolution using both gradient-echo and spin-echo EPI. Paradigms were designed to activate primary visual cortex (V1/V2) and more specialized areas associated with detection of color (V4) and motion (V5). Sensitivity of activation maps increased at higher resolution despite the decreased total signal intensity at the smaller voxel size, presumably from reduced partial volume averaging. The greater microvascular selectivity of high-resolution spin-echo imaging enabled distinct activation patterns sensitive to motion to be detected in V1/V2 that were not apparent with gradient-echo imaging. The spatial resolution at 3.0 tesla was constrained by the size of physiological head motion relative to the voxel dimensions rather than SNR or the hemodynamic response of BOLD contrast. The higher spatial resolution at 3.0 tesla with more selective spin-echo EPI can further refine functional mapping within the cerebral cortex.