Healthy brain. Coloured computed tomography (CT) scan of a human head. The axial (horizontal) scan has revealed the head and brain in cross section. The front of the head is at top. The dark areas (centre), the ventricles, lie between the two hemispheres. The ventricles are spaces filled with cerebrospinal fluid, the fluid that surrounds and protects the brain and spinal cord. The dark areas in the skull (pale) towards the front of the head (top) are the frontal sinuses, air spaces lined with mucous membranes. The brain (orange) fills the remainder of the skull. CT scanning uses beams of X-rays fired at different angles to build up slice images through the body. It is useful for detecting many brain disorders such as haemorrhages or tumours.