Brain tumour. Coloured 3D diffusion tensor imaging (DTI) and magnetic resonance imaging (MRI) scans of the brain of a 29 year old with a low grade glioma in the left frontal lobe. A DTI scan shows the bundles of white matter nerve fibres and is being used here for pre-surgical planning. The fibres transmit nerve signals between brain regions and between the brain and the spinal cord. A glioma arises from glial cells, nervous system support cells. DTI scans show the diffusion of water along white matter fibres, allowing their orientations and the connections between brain regions to be mapped.