You lie on a special couch while it moves through a large hollow ring. X-rays pass through your body, and a picture is displayed on a TV screen. Many pictures may need to be taken, but each one takes only a few seconds.

You will be asked to drink a liquid contrast medium (dye), which shows up on X-ray. Halfway through the scan (which takes only a few minutes) you may be injected in the arm with another dye that will show up the veins in your liver. This may make you flush hot all over for several minutes. Your doctor will tell you what to expect beforehand.

The dose of X-ray radiation is more than for an ordinary X-ray, but still within levels considered a low risk, so a CT scan is regarded as safe. Rarely, some people are allergic to the dye, but this can be treated straightaway.