Healthy brain and eyes. Coloured computed tomography (CT) scan of a human head. The axial (horizontal) scan has revealed the head and brain in cross section at eye-level. The front of the head is at top. The circular structures at the top are the eyeballs. Between them are the sinuses (dark), air spaces lined with mucous membranes. The brain (orange) fills the remainder of the skull (pale). 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.