The short answer
A CT scan uses special x-ray equipment to make detailed pictures of the inside of your body. You lie still on a table that passes through a donut-shaped machine, sometimes holding your breath. You may get a contrast dye to make pictures clearer. The scan is painless, usually outpatient, and takes a few minutes to half an hour.
A CT scan uses special x-ray equipment to make detailed picture 'slices' of the inside of your body.
You lie still on a table that passes slowly through a large donut-shaped machine, and may be asked to hold your breath briefly.
You may receive a contrast dye, by mouth, injection, or enema, to make the pictures clearer.
Contrast reactions are rare; tell the technologist right away about any itching, hives, shortness of breath, or swelling.
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The full explanation.
The short version
A CT scan is one of the most common imaging tests used in cancer care, and knowing what actually happens can take away a lot of the mystery. It is a noninvasive test — nothing is inserted into your body during the scan itself — that uses special x-ray equipment and a computer to create detailed pictures of the inside of your body, arranged as thin "slices."
Before the scan
Depending on the reason for your scan, you may be asked to change into a gown and remove jewelry or metal items that could interfere with the pictures. You may also be given a contrast dye to help make the pictures clearer. Contrast can be given by mouth, injected into a vein, or given by enema, and common contrast materials include iodine and barium. If you might be pregnant, tell the staff before your scan.
During the scan
You will lie very still on a table that passes slowly through the center of a large, donut-shaped machine. As the machine works, you may hear whirring sounds, and you may be asked to hold your breath for a few seconds at a time to keep the pictures from blurring.
The scan itself is not painful, though lying still in one position can feel slightly uncomfortable, especially if the scan takes a while. Most CT scanners only surround part of your body at a time rather than your entire body, so people are unlikely to feel claustrophobic during a CT scan.
About the contrast dye
If your scan uses contrast, it is meant to make the pictures clearer so your care team can 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, but it is important to tell the technologist right away if you notice any of these signs so they can help.
How long it takes
A CT scan is usually done as an outpatient test, meaning you do not stay overnight. The scan itself usually lasts anywhere from a few minutes to about half an hour, depending on what part of your body is being imaged and whether contrast is used.
About the radiation
CT scans use a small amount of ionizing radiation to create their pictures. The increased cancer risk from a single CT scan is small, and for most people, the benefits of getting the information the scan provides outweigh that small risk. If you have questions about how many scans you have had or are likely to need, your care team can talk through that with you.
After the scan
Once the scan is finished, you can usually go about your day unless your care team tells you otherwise. If you received contrast, ask your team whether you should do anything afterward, such as drinking extra fluids.
Questions for your team
It is worth asking ahead of time whether you will need contrast, how long the scan is expected to take, and whether there is anything specific you should do to prepare. Knowing the plan in advance can make the whole appointment feel much more predictable.
Words to know
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Common questions
▸Does a CT scan hurt?
No, a CT scan is not painful. You may find it slightly uncomfortable to lie still for the length of the scan, but the scan itself does not hurt.
▸What happens during the scan?
You lie very still on a table that passes slowly through the center of a large donut-shaped machine. You may hear whirring sounds, and you may be asked to hold your breath at points to keep the pictures from blurring.
▸Why might I need contrast dye?
A contrast dye can be given by mouth, injected into a vein, or given by enema to make the pictures clearer. Common contrast materials include iodine and barium.
▸Is contrast dye safe?
Reactions are rare. Some people have a mild reaction like itching or hives; more serious reactions like shortness of breath or swelling are rarer still. Tell the technologist right away if you notice any of these signs.
▸Will I feel claustrophobic during a CT scan?
Most CT scanners only surround part of your body at a time, so people are unlikely to feel claustrophobic during a CT scan.
Questions to ask your doctor
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Your next step
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