Glioblastoma brain tumour. 3D diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan of nerve pathways (coloured) around a glioblastoma (upper right) in the brain. The brain is seen from the side, with the front of the brain at left. Glioblastoma is the most common malignant primary brain tumour. Symptoms depend on the region of the brain affected, and include seizures, headaches, weakness on one side of the body, and memory and personality changes due to the growth of the cancer. Diffusion tensor imaging (tractography) measures the direction of water diffusion, which in the brain reveals the orientation of nerve fibres.