Coloured diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan showing white matter fibres in the brain. The back of the brain is at bottom left. The structures shown here are the fornix, inferior longitudinal fibres, cingulum hippocampal fibres, cingulum, inferior fronto-occipital fibres, thalamic prefrontal fibres and uncinate fasciculus pathway. 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.