What to Expect During a CT Scan

A CT scan is one of the most common imaging tests used in cancer care. Knowing what actually happens takes away a lot of the mystery. It is a noninvasive test, so nothing is put inside your body during the scan itself. It uses special x-ray equipment and a computer to build detailed pictures of the inside of your body, arranged as thin "slices."

Depending on the reason for your scan, you may be asked to change into a gown. You may also need to remove jewelry or metal items that could blur the pictures. Many scans use a contrast dye to make the images clearer. Contrast can be given by mouth, injected into a vein, or given by enema. Common contrast materials include iodine and barium. If you might be pregnant, tell the staff before your scan.

You lie very still on a table. The table passes slowly through the center of a large, donut-shaped machine. You may hear whirring sounds as the machine works. You may also be asked to hold your breath for a few seconds at a time, so the pictures do not blur.

The scan itself is not painful. Lying still in one position can feel slightly uncomfortable, especially if the scan takes a while. Most CT scanners surround only part of your body at a time, so people rarely feel closed in.

If your scan uses contrast, it is there to make the pictures clearer. That helps your care team see certain areas more easily. Reactions to contrast are rare. Some people have a mild reaction, such as itching or hives. More serious reactions, such as shortness of breath or swelling, are rarer still. Tell the technologist right away if you notice any of these signs, so they can help.

A CT scan is usually done as an outpatient test, so you do not stay overnight. The scan itself can last from a few minutes to about half an hour. The time depends on which part of your body is being imaged, and whether contrast is used.

CT scans use a small amount of ionizing radiation to create their pictures. The added cancer risk from a single CT scan is small. For most people, the information the scan gives is worth that small risk. If you have questions about how many scans you have had, or are likely to need, your care team can talk that through with you.

Once the scan is finished, you can usually go about your day. Your care team will tell you if anything is different for you. If you received contrast, ask whether you should do anything afterward, such as drinking extra fluids.

Ask ahead of time whether you will need contrast. Ask how long the scan is expected to take. Ask whether there is anything specific you should do to prepare. Knowing the plan in advance can make the whole appointment feel much more predictable.

If you had contrast dye, a small number of reactions begin after you have left.

• Call 911 or go to an emergency department if your lips, tongue or throat start to swell, your breathing tightens, or you feel faint in the hours after the injection.
• Call your care team the same day if an itchy rash or hives spreads, or you keep vomiting once you are home.
• Call your care team within a day or two if you have kidney trouble or diabetes and notice you are passing much less urine than usual, or your ankles puff up.

Source: MedlinePlus (National Library of Medicine, NIH) — CT Scan.