Computed Tomography (CT) Scan—What to Expect

A computed tomography (CT) scan, also called a CAT scan, is a diagnostic examination used to detect cancer and find out the cancer’s stage (a way of describing a cancer, such as where it is located, whether or where it has spread, and whether it is affecting the functions of other organs in the body). Staging helps the doctor decide what kind of treatment is best and predict a patient’s prognosis (chance of recovery). CT scans can also be used to guide some types of biopsies (the removal of a small amount of tissue for examination to determine whether cancer is present) or to evaluate the effectiveness of cancer treatments, such as chemotherapy or radiation therapy. Common areas that may be scanned include the head, neck, chest, abdomen, pelvis, or limbs.

A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. Sometimes, a contrast medium (a special dye) is injected into a patient’s vein to provide better detail in the images. One risk of this test is radiation exposure. Usually, the potential benefit outweighs the risk; however, if you are receiving multiple CT scans and x-rays, talk with your doctor about whether another type of test that involves less exposure to radiation can be done.

In some cases, your doctor may recommend an integrated PET-CT scan. This combines the images from a positron emission tomography (PET) scan and a CT scan, performed at the same time on the same machine. Together, the two scans create a more complete image than either test can offer alone. Learn more about what to expect with an integrated PET-CT scan.

The medical team

A CT scan is performed at the radiology department of a hospital or at an outpatient imaging center. It is performed by a radiologist (a doctor who performs and interprets imaging tests to identify problems in the body) or radiologic technologist (a health care professional who is specially trained and certified to operate a CT scanner).

Preparing for the procedure

When you schedule the examination, you will get detailed instructions on how to prepare.

Tell your doctor or nurse about all medications you are taking and ask whether you should take them on the day of the test. In addition, discuss any drug allergies you have, especially any allergic reactions to iodine that you may have experienced. In addition, be sure to mention any other medical conditions you have.

Women should tell their doctors if they are breast-feeding or if there is any chance that they are pregnant because a CT scan could put the baby at risk.

You may be told to drink only clear liquids starting at midnight the night before your examination and instructed to not eat or drink anything for at least four hours prior to your scan. However, for scans of some parts of the body, there will not be restrictions on eating prior to the examination.

Ask whether you can bring your own music; some facilities allow patients to listen to music during their examinations.

You will be asked to sign a consent form that states you understand the benefits and risks of the CT scan and agree to undergo the test. Talk with your doctor about any concerns you have about the CT scan.

During the procedure

When you arrive for your CT scan, you may need to change into a hospital gown or remove clothing or jewelry that could interfere with the scan. This includes belts, earrings, shirts with snaps or zippers, bras, and glasses.

Depending on which part of your body is targeted, you may receive a contrast agent (a special dye). It may be given orally (as a drink) or through an intravenous (IV) injection. The dye travels through your bloodstream and helps to create a clearer picture of specific parts of your body.

If you are given an injection, you may feel heat or itching at the injection site or have a metallic taste in your mouth; both sensations should disappear after a few minutes. If you experience a more serious reaction, tell the technologist immediately.

The technologist will help position you on an exam table. The table may have straps, pillows, or a special cradle for your head to hold you in place. You will probably lie on your back, although you may be asked to lie on your side or your stomach, depending on which part of your body is being scanned, especially if you are undergoing a biopsy.

During the examination, the technologist who monitors the procedure will be in an adjoining control room, but he or she will be able to observe you through a window or by means of a video camera, and you will be able to communicate through an intercom system.

The CT scanner resembles a large donut. The exam table will slide back and forth through the large hole in the center of the machine as the scanner rotates around you. For the first scans, the table will move rapidly through the scanner, which helps the technologist confirm that your body is properly positioned. For the remaining scans, the table will move more slowly.

CT scans are not painful. However, you will need to lie still for the entire scan, which may become uncomfortable. Since the scanner is shaped like a donut, you will not be enclosed in the scanner at any time. You can also expect to hear whirring or clicking sounds from the machine; some machines are noisier than others.

You may be asked to hold your breath during part of the scan because the motion created by breathing can blur the images. The exam table may be raised, lowered, or tilted to create the correct angle for the x-rays; ask the technologist performing the scan to tell you when the table will move.

The examination will generally last up to an hour, although the scanning itself takes only 10 to 15 minutes or less. Newer scanners, including spiral or helical CT scanners, are even faster. If a larger part of your body is being scanned, the procedure may last longer. The technologist should be able to give you a time estimate before you begin.

When the scan is finished, you may be asked to remain on the exam table while a radiologist reviews the images to determine whether additional images are needed.

After the procedure

You can expect to resume your normal activities immediately after your CT scan, including driving. If you received a contrast agent for the scan, you may be told to drink a lot of water to flush it out of your body.

Integrated PET-CT Scan—What to Expect

An integrated PET-CT scan combines the images from a positron emission tomography (PET) scan and a computed tomography (CT) scan, performed at the same time on the same machine. Together, the two scans create a more complete image than either test can offer alone.

Like the individual tests that it combines, an integrated PET-CT scan is a diagnostic examination used to detect cancer and find out the cancer’s stage (a way of describing a cancer, such as where it is located, whether or where it has spread, and whether it is affecting the functions of other organs in the body). Staging helps the doctor decide what kind of treatment is best and predict a patient’s prognosis (chance of recovery). The scan can also be used to locate an area for a biopsy (the removal of a small amount of tissue for examination under a microscope to determine whether cancer is present) or to evaluate the effectiveness of cancer treatments, such as chemotherapy or radiation therapy.

About PET and CT scans

A PET scan creates pictures of organs and tissues inside the body. A small amount of a radioactive substance is injected into a patient’s body. This substance is absorbed mainly by organs and tissues that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body. The risks associated with exposure to such a small dose of radiation through a PET scan are minimal and are outweighed by the benefits of the test.

Meanwhile, a CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. Sometimes, a contrast medium (a special dye) is injected into a patient’s vein to provide better detail in the images.

One risk of this test is radiation exposure. It is minimal for the PET scan portion of the test, and the radioactive substance remains in your body only for a short time. However, there is more radiation exposure associated with the CT scan part of the procedure. Usually, these risks outweigh the potential benefit; however, if you are receiving multiple CT scans and x-rays, talk with your doctor about whether another type of test that involves less exposure to radiation can be done.

The medical team

An integrated PET-CT scan is given at the radiology or nuclear medicine department of a hospital or at an imaging center. It is performed by a radiologist (a doctor who performs and interprets imaging tests to identify problems in the body) or radiologic technologist (a health care professional who is specially trained and certified to operate PET-CT scanners, among other types of nuclear medicine).

Preparing for the test

When you schedule the test, you will receive detailed instructions about how to prepare. For example, you may be told to drink only clear liquids beginning at midnight the night before your examination and instructed to not eat or drink anything during the four hours before your scan.

You will be asked to sign a consent form that states you understand the benefits and risks of the PET-CT scan and agree to undergo the test. Talk with your doctor about any concerns you may have about the scan.

In addition, tell your doctor about all medications you are taking, and ask whether you should take them on the day of the test. Also discuss any drug allergies or other medical conditions you have, especially any allergic reactions to iodine that you may have experienced. Women should tell their doctors if they are breast-feeding or if there is any chance that they may be pregnant because a PET-CT scan could put the baby at risk.

Some facilities allow patients to listen to music during the scan, so you may want to ask whether you can bring your own music to make you more comfortable.

During the test

When you arrive for the PET-CT scan, you may need to change into a hospital gown or remove clothing or jewelry that could interfere with the scan.

A radiation technologist or nurse will then deliver radioactive substance needed for the PET scan into your vein through an intravenous (IV) injection. The IV line will feel like a pinprick when it is inserted, but the radioactive material will not create any sensation in your body.

After the injection, the radioactive substance will take 30 to 90 minutes to reach the tissues that will be scanned. During that time, you will need to lie quietly without moving or talking; too much motion can affect the sites where the radioactive substance accumulates.

Depending on which part of your body is targeted, you may also be given a contrast agent (a special dye) for the CT scan. It may be given orally (as a drink), through an IV line, or through an injection. The dye travels through your bloodstream and helps to create a clearer picture of specific parts of your body.

If you are given the dye through an injection, you may feel heat or itching at the injection site or have a metallic taste in your mouth; both sensations should disappear after a few minutes. If you have a severe reaction, tell the radiation technologist immediately.

When it is time for the test to begin, a technologist will help position you on a padded exam table outside of the PET-CT scanner. The table may have straps, pillows, or a special cradle for your head to help hold you in place. You will probably lie on your back, although you may be asked to lie on your side or your stomach, depending on which part of your body is being scanned.

During the examination, a technologist will monitor the test through a window or a video screen in a nearby control room, and you will be able to communicate through an intercom system.

The PET-CT scanner resembles a large donut. The exam table will slide back and forth through the large hole in the center of the machine as the scanner rotates around you. For the first scans, the table will move rapidly through the scanner, which helps the technologist confirm that your body is properly positioned. For the remaining scans, the table will move more slowly. The scans are done sequentially—first the CT scans, then the PET scans.

A PET-CT scan is not painful. However, you will need to lie still for the entire scan, and you may need to keep your arms raised above your head, which could become uncomfortable. In addition, you may be asked to hold your breath during part of the scan because the motion created by breathing can blur the images. The exam table may be raised, lowered, or tilted to create the correct angle for the scan; ask the technologist performing the scan to tell you when the table will move. You can also expect to hear whirring or clicking sounds from the machine; some machines are noisier than others.

The appointment typically lasts up to an hour, although the scan itself takes only about 30 minutes. If a larger part of your body is being scanned, the procedure may last longer. The technologist should be able to give you a time estimate before you begin.

When the scan is finished, you may be asked to remain on the exam table while a radiologist reviews the images. If the images are blurred or otherwise unreadable, you may need to have an additional scan.