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Pelvis. A CT scan can look for problems of organs in the pelvis. For a woman, these include the uterus, ovaries, and fallopian tubes. For a man, the pelvic organs include the 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 foot.

A 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 abscess.

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 dyes.
  
• Have a heart condition, such as heart failure.
  
• Have diabetes or take metformin (Glucophage) for your diabetes. You may have to adjust your medicine for a day before and after the test.
  
• Have had kidney problems.
  
• Have asthma.
  
• Have a medical device, such as a pacemaker or an insulin pump.
  
• Have had multiple myeloma.
  

Have had an X-ray test using barium contrast material (such as a barium enema) or have taken a medicine that contains bismuth (such as Pepto-Bismol) in the past 4 days. Barium and bismuth show up on X-ray films and make 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?).

A CT scan is usually done by a radiology technologist. The pictures are usually read by a radiologist, who writes the report. Other doctors, such as a family medicine doctor, internist, or surgeon, also may review a CT scan.

You 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 test.

During the test, you will lie on a table that is attached to the CT scanner, which is a large doughnut-shaped machine.

The 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 scanning room. But the technologist will watch you through a window. You will be able to talk to the technologist through a two-way intercom.

If dye (contrast material) is needed, it will be given in one of several ways, depending on the body area being studied.

• Contrast material may be given in a vein (IV) in the arm for chest, belly, and pelvic CT scans.
  
• You may drink contrast material for a belly CT, or it may be put through a tube into your bladder or rectum, or it may be put through a thin needle into a joint.
  

A CT scan usually takes 15 to 30 minutes.

Drink lots of liquids for 24 hours after the scan to help flush the dye out of your body.

You will not have pain during the test. 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 scanner.

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 small.

• There is a chance of an allergic reaction to the dye (contrast material).
  
• 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 slight chance of developing cancer from having some types of CT scans.¹ The chance 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 amount of radiation this test may give you or your child and confirm that the test is needed.
  
• There is a slight risk that the CT scan can interfere with implanted or external medical devices. Examples of medical devices include pacemakers, insulin pumps, defibrillators, and neurostimulators.
  

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

The radiologist may discuss the CT scan with you right after the test. Complete results usually are ready for your doctor in 1 to 2 days.

CT scanNormal: Abnormal:

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 present.

No bleeding or collections of fluid are present.

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

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

Kidney stones or gallstones are present.

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

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

An aneurysm is present.

Blockage is found in the intestines or in the bile ducts.

A CT of the belly shows inflammatory bowel disease or diverticulitis.

Lymph nodes are enlarged.

One or more blood vessels are blocked.

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

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

• Pregnancy. CT scans are not usually done during pregnancy.
  
• Barium and bismuth used for another test. These substances show 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.
  
• You are not able to lie still during the test.
  
• 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
  

• 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.