High spatial resolution functional magnetic resonance imaging at very- high-magnetic field

Although neuroimaging methods have been used successfully to map large- scale neurocognitive networks distributed across the human cortex, functional mapping and differentiation of localized brain organization within a small structure has been limited by inadequate sensitivity for high spatial resolution imaging. Functional magnetic resonance imaging (fMRI) technique based on blood oxygenation level-dependent (BOLD) contrast has become one of the most useful neuroimaging techniques. It has been used extensively to study human brain function from sensory perception to cognitive performance. However, the majority of these studies used a relatively low spatial resolution (typically with a voxel size of 3.1 x 3.1 x 5.0 mm³), which is incapable of mapping on the millimeter and submillimeter spatial scale. In this article, we review the technical aspects of the high-resolution fMRI technique and the sensitivity and spatial specificity of BOLD-based fMRI. We demonstrate applications of high-resolution fMRI in studying the human visual pathway from the lateral geniculate nucleus in the thalamus to the ocular dominance columns in the primary visual cortex. Most results were obtained at very-high-magnetic fields (3.0 and 4.0 Tesla). They reveal that high- resolution fMRI at very-high-magnetic field is promising for functional mapping of brain organization from large cortical networks, small nuclei, and even to cellular layer structures.