CT Scan for Cancer

A CT scan can be used to find cancer, determine treatment, or plan further cancer treatment. You might also hear it called a CAT scan, a computed tomography scan, or a spiral or helical CT.

What is a CT scan?

A CT scan is an imaging test that combines many x-ray pictures to create a detailed view of a specific area in the body. It can help doctors find cancer and see the shape and size of a tumor.

CT scans are painless, but you may have temporary taste changes or a feeling of warmth if you get contrast dye before the test. The scan usually takes less than 30 minutes, depending on the body part being looked at.

What does a CT scan show?

A CT scan shows a series of slices, or a cross-section, of your body. The image shows bones, organs, and soft tissues more clearly than standard x-rays.

A CT scan can show:

• A tumor’s shape, size, location, and nearby blood vessels
• If a cancer has spread or metastasized
• If a tumor is responding to treatment or if the cancer has come back, by comparing CT scans done over time

It can also help doctors:

• Find the right place for a biopsy. This is called a CT-guided biopsy.
• Guide a needle into a tumor for some cancer treatments, such as radiofrequency ablation (RFA), a type of treatment that uses heat to destroy a tumor.
• Plan radiation therapy for cancer treatment.

How does it work?

A CT scan uses a pencil-thin beam of radiation to create a series of pictures taken from different angles. These pictures are combined to create a detailed 2-dimensional (2D) image of a single section of the body. This looks much like a single slice from a loaf of bread.

Many images can also be combined to create 3-dimensional (3D) images. This may be especially helpful in planning a biopsy, surgery, or other treatments, such as ablations. The images allow doctors to see even more detail, including how a tumor relates to nearby blood vessels and organs. The 3D pictures can be rotated on a computer screen to look at different angles.

To get a clearer picture, special contrast materials are sometimes used. These are swallowed as a liquid, put into a vein, or put into the intestines through the rectum as an enema.

Virtual endoscopy

Virtual endoscopy takes CT technology one step further by allowing doctors to look at the inside surfaces of organs without actually putting scopes into a person’s body. This includes organs such as the:

• Lungs (virtual bronchoscopy)
• Colon (virtual colonoscopy or CT colonography)

The 3-D CT images are arranged to create a black and white view on the computer screen that looks a lot like the view a doctor sees during an actual endoscopy.

How do I get ready for the scan?

CT scans can be done at an outpatient clinic or medical office. You don’t have to be in a hospital.

You might be told to stop eating or drinking overnight or for several hours before the test. In some cases, you might need to use a laxative or an enema. This cleans out your bowel so doctors have a clear view inside your belly and intestines.

What is it like having a CT scan?

For your safety and to get the best images, you may be asked to:

• Undress and put on a gown
• Remove underwire bras, jewelry, piercings, glasses, or other metal objects
• Remove dentures, hearing aids, hair clips, and other items

A radiology technologist (tech) does the CT scan. Let them know if you have a pacemaker, infusion port, or other implanted medical device. This won’t keep you from getting a CT scan, but extra care can be taken if that area is scanned.

During the scan

The scanner is a large, doughnut-shaped machine. You will lie on a thin, flat table that slides back and forth inside the hole in the middle of the scanner.

As the table moves into the opening, an x-ray tube rotates within the scanner, sending out many tiny x-ray beams at precise angles. These beams quickly pass through your body and are detected on the other side of the scanner. You may hear buzzing and clicking as the scanner switches on and off.

You will be alone in the exam room during the CT scan, but the tech will be able to see, hear, and talk to you at all times.

A CT scan is painless, but you may find it uncomfortable to hold still in certain positions or hold your breath for a short time. Holding still is important because chest and body movements can affect the image.

Other steps to prepare

Depending on the type of scan you need, the radiology tech may take other steps to prepare you.

For example, your head may be held still in a special device during a head CT. For a CT colonography, air is pumped into your colon to help see the inner bowel surface. This may cause discomfort or a feeling of fullness.

Getting contrast dye

Depending on the part of your body being scanned, you might get contrast dye as a drinkable liquid, an IV injection, or an enema right before the test.

Contrast liquid: Contrast liquid can taste unpleasant, but most people tolerate it well.

IV injection: Contrast dye might be given through an IV. You’ll probably have one CT scan, get the contrast dye, then have a second scan. As you get the IV contrast, you may feel warmth spreading through your body. Some people say this feels like they “wet their pants.” This is only a feeling, and it goes away quickly. You might also get a bitter or metallic taste in your mouth that can last for several hours.

How long does a CT scan take?

A CT scan usually takes less than 30 minutes, but this varies depending on the body part being scanned and if contrast dye is used. It often takes more time to get you into position and give you the contrast dye than it does to take the pictures. The total time for your visit may vary.

After the test, you might be asked to wait while the pictures are reviewed, to make sure they are clear and show everything. If not, you may need another scan.

What are the possible risks and side effects?

Some people may react to the contrast dye used for CT scans. Possible reactions include:

• Rash
• Nausea or vomiting
• Flushing
• Feeling of warmth
• Itchy or scratchy throat
• Taste changes

Most symptoms are usually mild and often go away on their own, but they can be a sign of a more serious reaction that needs to be treated. Let your health care team know if you have any of these problems.

Severe reactions: In rare cases, people can have a severe reaction that causes blood pressure issues or breathing problems like shortness of breath or wheezing. This must be treated right away. Tell your health care team if you notice any changes after getting the contrast dye.

Kidney problems: The IV contrast dye can also cause kidney problems. This is rare, and it’s more common in someone whose kidneys already don’t work well. If you need a scan with contrast dye, your health care team might first do a blood test to check your kidney function. They might also give you extra fluids in an IV or medicines to help your kidneys get rid of the dye safely.

What else should I know about a CT scan?

• Although a CT scan is sometimes described as a “slice” or a “cross-section,” no cutting is involved.
• The amount of radiation you get during a CT scan is more than a standard x-ray. For low-dose CT scans, the radiation amount is much less than a regular CT scan.
• People with excess body weight may have trouble fitting into the CT scanner. If this applies to you, your health care team will talk with you about your options.
• Tell your health care team if you could be pregnant or are breastfeeding.
• CT scans can cost more than a standard x-ray. Before you have the test, check with your health insurance plan to see if it is covered.

Low-dose CT scan (LDCT) for lung cancer screening

Certain CT scans may be used for cancer screening. For example, screening for lung cancer is done with a low-dose CT scan (LDCT) in people who are at higher risk for lung cancer.

The American Cancer Society (ACS) recommends yearly screening with an LDCT for people ages 50 to 80 years old who smoke or used to smoke and have at least a 20 pack-year* history of smoking. A pack-year is equal to smoking 1 pack (or about 20 cigarettes) per day for a year.

See Can Lung Cancer Be Found Early? to learn more about lung cancer screening.

Learn more

• Imaging Tests for Cancer