Human: I've been told that I need to have a CT scan, but I'm not sure what it is. What does it involve? Assistant: 
A CT scan (or computed tomography) is a medical imaging technique that uses X-rays to create cross-sectional images of the body. It is used to diagnose and stage various diseases, including cancer. During a CT scan, the patient lies on a table that slides into a large machine. The patient’s head is then held still while an X-ray tube rotates around them. This creates multiple pictures or slices of the body, which are then compiled together by computer software to form a 3D image.