Corpus callosum. Coronal 3D diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan of nerve pathways (red) in the brain's corpus callosum. The corpus callosum is the band of nerve fibres that connects the two hemispheres of the brain (left and right). Diffusion tensor imaging measures the direction of water diffusion, which in the brain reveals the orientation of nerve fibres. The technique is also known as tractography, with the resulting image known as a tractogram.