How does computerised tomography (CT) work?
In computerised tomography the patient lies on a couch passing through the doughnut-shaped scanner. X-ray beams are sent through the body from a source to a ring of detectors. Tissues absorb different amounts of energy from the X-rays depending on their density. The X-ray source rotates around the body and the ring of detectors collects information to send to the computer. The computer performs many thousands of calculations to turn this data into an image of a ‘slice’ through the body. The image can be viewed on a monitor or captured on film. As a digital image it can be rotated, coloured or many ‘slices’ combined to form a 3D image. What can you see with computerised tomography ? Compared to simple X-ray, the precision of CT makes it ideal for defining the boundaries between different tissues. It can be used to measure enlarged organs or the position, size and shape of tumours when planning radiotherapy or surgery. Images with the text: CT scan of the abdomen, c.2000. The scan shows
