Coloured diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan showing white matter fibres in the brain. The front of the brain is at bottom right. The structures shown here are the inferior fronto-occipital fibres, thalamic parietal fibres, thalamic precentral fibres and the thalamic postcentral fibres. Diffusion tensor imaging measures the direction of water diffusion, which in the brain reveals the orientation of nerve fibres. Red fibres have a left to right orientation, green a front to back orientation and blue an up and down orientation.