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 fibers and is being used here for presurgical planning. The fibers transmit nerve signals between brain regions and between the brain and the spinal cord. A glioma arises from glial cells; nervous system supports cells. DTI scans show the diffusion of water along white matter fibers, allowing their orientations and the connections between brain regions to be mapped.