Very high-resolution three-dimensional functional MRI of the human visual cortex with elimination of large venous vessels

We propose a very high-resolution, three-dimensional (3D) gradient-echo technique with a twofold parallel imaging acceleration using a specialized occipital receiver coil at 3 T to perform functional MRI (fMRI) of the visual cortex. This configuration makes it possible to acquire 3D fMRI data within a timescale compatible with a block design. Without further processing, the functional maps at an isotropic 3D resolution of 0.42 microL (0.75 mm voxel size) and near-isotropic resolution of 1.2 microL (1 mm voxel size) show very robust activation in visual areas, but with clear contamination from larger veins. As this technique allows direct identification of veins in the functional scan, it permits removal of their effect from the activation maps. In our study, elimination of veins qualitatively improves the spatial specificity of activation maps, while reducing the activated volume by about 25%. The proposed technique provides functional information at the resolution of anatomical scans, is localized to gray matter, and facilitates functional to anatomical co-registration because of minimal distortions.