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, pancreas, intestines, kidneys, bladder, adrenal glands, lungs, and heart. It also can study
blood vessels, bones, and the spinal cord.
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.
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 jaundice.
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.
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
How To Prepare
Before the CT scan, tell your doctor
Are or might be pregnant.
Are allergic to any medicines, including iodine
Have a heart condition, such as
Take metformin. You may have to adjust your medicine for a day before and
after the test.
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.
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
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.
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.
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.
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.
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.
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: http://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 ReviewerAdam Husney, MD – Family Medicine E. Gregory Thompson, MD – Internal Medicine Specialist Medical ReviewerHoward Schaff, MD – Diagnostic Radiology