Brain fibres. 3D diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan of nerve pathways in the brain. The pathways are highlighted in blue. The brain is seen from the side, with the front of the brain at 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.