Brain tumour. Coloured 3D diffusion tensor imaging (DTI) scan of the brain of a 64 year old with a sphenoid wing meningioma. A DTI scan shows the bundles of white matter nerve fibres, which have been distorted by the tumour. The fibres transmit nerve signals between brain regions and between the brain and the spinal cord. A meningioma arises from the meninges (membranes) that surround the brain and spinal cord. DTI scans show the diffusion of water along white matter fibres, allowing their orientations and the connections between brain regions to be mapped.