Test Overview

A computed tomography (CT) scan uses
X-rays to make detailed pictures of structures inside
of the body.

During the test, you will lie on a table that is
attached to the CT scanner, which is a large doughnut-shaped machine. The CT
scanner sends X-rays through the body area being studied. Each rotation of the
scanner provides a picture of a thin slice of the
organ or area. All of the pictures are saved as a
group on a computer. They also can be printed.

In some cases, a
dye called contrast material may be used. It may be put in a vein (IV) in your
arm, or it may be placed into other parts of your body (such as the
rectum or a joint) to see those areas better. For some
types of CT scans, you drink the dye. The dye makes structures and organs easier to see on the CT

A CT scan can be used to study all parts of your
body, such as the chest, belly, pelvis, or an arm or leg. It can take pictures
of body organs, such as the liver,
adrenal glands, lungs, and heart. It also can study
blood vessels, bones, and the spinal cord.

Fluoroscopy CT
is a special test that is not widely available. It uses a steady beam of X-rays
to look at movement within the body. It allows the doctor to see your organs
move or to guide a
biopsy needle or other instrument into the right place
inside your body.

Why It Is Done

CT scans are used to study areas of
the body and the arms or legs.

  • Chest (thorax). A CT scan of the chest can look for
    problems with the lungs, the heart, the
    esophagus, or the major blood vessel (aorta) or the tissues in the center of the chest.
    Some common chest problems a CT scan may find include infection,
    lung cancer, a
    pulmonary embolism, and an
    aneurysm. It also can be used to see if cancer has
    spread into the chest from another area of the body.
  • Abdomen. A CT scan of the abdomen can find
    abscesses, infection, tumors, an aneurysm, enlarged
    lymph nodes, foreign objects, bleeding in the belly,
    inflammatory bowel disease, and
  • Urinary tract. A CT scan of the kidneys,
    ureters, and bladder is called a CT KUB or CT urogram.
    This type of scan can find
    kidney stones, bladder stones, or blockage of the
    urinary tract. A special type of CT scan, called a CT intravenous
    pyelogram (IVP), uses injected dye (contrast material) to look for kidney stones, blockage, growths, infection, or
    other diseases of the urinary tract.
  • Liver. A CT scan can find liver tumors, bleeding
    from the liver, and liver diseases. A CT scan of the liver can help determine
    the cause of
  • Pancreas. A CT scan can find a tumor in the
    pancreas or inflammation of the pancreas (pancreatitis).
  • Gallbladder and bile ducts. A CT scan can be used
    to check for blockage of the
    bile ducts.
    Gallstones occasionally show up on a CT scan. But
    other tests, such as
    ultrasound, usually are used to find problems with the
    gallbladder and bile ducts.
  • Adrenal glands. A CT scan can find tumors or
    enlarged adrenal glands.
  • Spleen. A CT scan can be used to check for an
    injury to the
    spleen or the size of the spleen.
  • Pelvis. A CT scan can look for problems of organs
    in the pelvis. For a woman, these include the
    ovaries, and
    fallopian tubes. For a man, the pelvic organs include
    prostate gland and the
    seminal vesicles.
  • Arm or leg. A CT scan can look for problems of the
    arms or legs, including the shoulder, elbow, wrist, hand, hip, knee, ankle, or

Other uses for a CT scan

CT scan may be used to make sure a procedure is done correctly. For example,
the doctor may use CT to guide a needle during a tissue biopsy or to guide the
proper placement of a needle to drain an

For people with cancer, a CT
scan can help determine how much the cancer has spread. This is called staging
the cancer.

How To Prepare

Before the CT scan, tell your doctor
if you:

  • Are or might be pregnant.
  • Are allergic to any medicines, including iodine
  • Have a heart condition, such as
    heart failure.
  • Have
  • Take metformin. You may have to adjust your medicine for a day before and
    after the test.
  • Have had kidney
  • Have
  • Have had
    multiple myeloma.
  • Have had an X-ray test using barium
    contrast material (such as a
    barium enema) in the past 4 days. Barium shows up
    on X-ray films and makes it hard to see the picture clearly.
  • Become
    very nervous in small spaces. You need to lie still inside the CT scanner, so
    you may need a medicine (sedative) to help you relax.

Arrange for someone to take you home in case you get a
medicine to help you relax (sedative) for the test.

If you have a
CT scan of your belly, you may be asked to not eat any solid foods starting the
night before your scan. For a CT scan of the belly, you may drink contrast
material. For some CT scans, you may need a laxative or an
enema before the test.

Talk to your
doctor about any concerns you have regarding the need for the test, its risks,
how it will be done, or what the results will mean. To help you understand the
importance of this test, fill out the
medical test information form (What is a PDF document?).

How It Is Done

A CT scan is usually done by a
radiology technologist. The pictures are usually read
by a
radiologist, who writes the report. Other doctors also may review a CT scan.

may need to take off any jewelry. You will need to take off all or most of your
clothes, depending on which area is studied. You may be able to wear your
underwear for some scans. You will be given a gown to use during the

During the test, you will lie on a table that is attached to
the CT scanner.

table slides into the round opening of the scanner, and the scanner moves
around your body. The table will move while the scanner takes pictures. You may
hear a click or buzz as the table and scanner move. It is very important to lie
still during the test.

During the test, you may be alone in the
scan room. But the technologist will watch you through a window. You
will be able to talk to the technologist through a two-way intercom.

The test will take about 30 to 60 minutes. Most of this time is spent getting ready for the scan. The actual scan only takes a few seconds.

How It Feels

The test will not cause pain.
The table you lie on may feel hard, and the room may be cool. It may be hard to
lie still during the test.

Some people feel nervous inside the CT

If a medicine to help you relax (sedative) or
dye (contrast material) is used, an IV is usually put in
your hand or arm. You may feel a quick sting or pinch when the IV is started.
The dye may make you feel warm and flushed and give you a metallic taste in
your mouth. Some people feel sick to their stomachs or get a headache. Tell the
technologist or your doctor how you are feeling.


The chance of a CT scan causing a problem is

  • There is a chance of an
    allergic reaction to the dye (contrast material).
  • If you breastfeed and are concerned about whether the dye used in this test is safe, talk to your doctor. Most experts believe that very little dye passes into breast milk and even less is passed on to the baby. But if you prefer, you can store some of your breast milk ahead of time and use it for a day or two after the test.
  • If you have diabetes or take metformin
    (Glucophage), the dye may cause problems. Your doctor will tell you when to
    stop taking metformin and when to start taking it again after the test so you
    will not have problems.
  • There is a small chance of getting
    cancer from some types of CT
    scans.footnote 1 The risk is
    higher in children, young adults, and people who have many
    radiation tests. If you are concerned about this risk, talk to your doctor
    about the benefits and risks of a CT scan, and confirm
    that the test is needed.


A computed tomography (CT) scan uses
X-rays to make detailed pictures of structures inside the body.

results usually are ready for your doctor in 1 to 2 days.

CT scan

The organs and blood vessels are normal in
size, shape, and location. No blood vessels are blocked.

No foreign objects (such as metal or glass
fragments), growths (such as cancer), inflammation, or infection are

No bleeding or collections of fluid are


An organ is too large or too small,
damaged, or infected. Abscesses are present.

Foreign objects (such as metal or glass
fragments) are present.

Kidney stones
gallstones are present.

Growths (such as tumors) are seen in the
colon, lungs,
ovaries, liver,
adrenal gland, or

A CT scan of the chest shows a
pulmonary embolism, fluid in the lungs, or

aneurysm is present.

Blockage is found in the intestines or in
bile ducts.

A CT of the belly shows
inflammatory bowel disease or

Lymph nodes are

One or more blood vessels are

A growth, fracture, infection, or other
problem is found in an arm or leg.

What Affects the Test

The following may stop you from
having the test or may change the test results:

  • Pregnancy. CT scans are not usually done during
  • Barium used for another test. Barium shows up on a CT scan. If a CT scan of the belly is needed, it should
    be done before any tests that use barium, such as a
    barium enema.
  • Metal objects in the body. These items, such
    as surgical clips or metal in joint replacements, may prevent a clear view of
    the body area.
  • You are not able to lie
    still during the test.

What To Think About

  • Sometimes your CT test results may be different
    than those from other types of X-ray tests,
    magnetic resonance imaging (MRI), or
    ultrasound scans because the CT scan provides a
    different view.
  • An ultrasound test, which doesn’t use dangerous radiation, may give results similar to those of a CT scan. If you are concerned about radiation exposure, ask your doctor if you can have an ultrasound instead of a CT scan.
  • Children who need a CT scan may need special
    instructions for the test. The child will likely need to hold his or her breath
    during the scan. If the child is too young to hold still or is afraid, the
    doctor may give the child a medicine (sedative) to
    help him or her relax.
  • If your child is scheduled for a CT scan,
    talk with your child’s doctor about the need for the scan and the risk of
    radiation exposure to your child.
  • Special
    CT scanners called spiral (helical) CT scanners and multi-slice (or
    multi-detector) CT scanners are sometimes used for this test. Many modern
    scanners are multi-slice scanners. These scanners can be used for many
    conditions, such as finding
    kidney stones, a
    pulmonary embolism, an enlarged
    prostate gland, or
    atherosclerosis. These special CT scanners can:

    • Take better pictures of blood vessels and
      organs so other imaging tests may not be needed.
    • Complete scans and
      provide pictures in less time.
  • CT results are often compared to positron
    emission tomography (PET) results to help find cancer. Some new scanners do
    both scans at the same time.
  • An electron beam CT scan is another
    type of CT scan that can find atherosclerosis and
    coronary artery disease. An electron beam CT scan is
    much faster than a standard CT scan and can take a good picture of a coronary
    artery while the heart is beating. Electron beam CT scans are not widely
    available. Another type of CT scanner, the multi-slice CT scan, is nearly as
    fast as electron beam CT scanners and is more widely available.
  • A
    CT angiogram can show two- and three-dimensional
    pictures of blood vessels and the heart.
  • Coronary calcium scans use a CT scan to check for early signs of coronary artery disease. This test is not advised for routine screening.
  • MRI may give different information than a CT scan about certain
    To learn more, see the
    Magnetic Resonance Imaging (MRI).
  • A low-dose CT is a way to scan the lungs more quickly than with a standard CT. Some doctors recommend this to screen for lung cancer in people who are older than 55 and who are at high risk for lung cancer.
  • Experts
    disagree about the use of a CT method called full-body scanning to screen for
    coronary artery disease and cancers. Full-body scanning is expensive, can lead
    to unnecessary tests or surgery, and may increase the chance of cancer from the
    radiation exposure. Most doctors do not recommend these studies unless a person
    has a specific risk for a certain disease.



  1. Einstein AJ, et al. (2007). Estimating risk of cancer associated with radiation exposure from 64-slice computed tomography coronary angiography. JAMA, 298(3): 317-323.

Other Works Consulted

  • Bluemke, D, et al. (2008). Noninvasive coronary artery imaging: Magnetic resonance angiography and multidetector computed tomography angiography. A scientific statement From the American Heart Association Committee on Cardiovascular Imaging and Intervention of the Council on Cardiovascular Radiology and Intervention, and the Councils on Clinical Cardiology and Cardiovascular Disease in the Young. Circulation, 118: 586-606.
  • Detterbeck FC, et al. (2013). Screening for lung cancer. Diagnosis and management of lung cancer, 3rd ed. American College of Chest Physicians evidence-based clinical practice guidelines. Chest, 143(5, Suppl): e78S-e92S.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • National Comprehensive Cancer Network (2010). Non-Small Cell Lung Cancer, version 2.2010. Available online: https://www.nccn.org/professionals/physician_gls/f_guidelines.asp.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
  • Pearce MS, et al. (2012). Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: A retrospective cohort study. Lancet, 380(9840): 499-505.
  • U.S. Food and Drug Administration (2008).
    FDA preliminary public health notification: Possible malfunction of electronic
    medical devices caused by computed tomography (CT) scanning. Available online:


ByHealthwise Staff
Primary Medical Reviewer Adam Husney, MD – Family Medicine
E. Gregory Thompson, MD – Internal Medicine
Specialist Medical Reviewer Howard Schaff, MD – Diagnostic Radiology

Current as ofOctober 9, 2017