CT Scan of the Body

A computed tomography (CT) scan is a special type of X-ray used to produce detailed pictures of the body's interior.

You may also want to see our info on CT scans of the head.

A CT scanner directs a series of X-rays through the body which are then computer-analyzed to create a cross-section view of the area being examined. Each X-ray pulse lasts only a fraction of a second, and it takes only a few seconds to capture each cross-section view. A CT scan produces clearer pictures of internal organs (such as the liver) than regular X-rays. The information captured can be stored on our computers for further study. The studies can also be used to produce photographs.

Just like with an X-ray, dense tissues in the body such as bones appear white. The less dense tissues, such as brain tissue or muscles, appear in shades of gray. Air-filled spaces, such as in the bowel or lungs, appear black.

During a body CT scan, the area being studied is positioned within a cylinder that is part of the CT scanner. The cylinder tilts and the X-ray devices within it can rotate to capture the required views. A CT scan is used to obtain information about the body's organs (such as the liver, pancreas, kidneys, adrenal glands, lungs, and heart), blood vessels, abdominal cavity, bones (especially of the spine), and the spinal cord.

Often a special dye (contrast material) that contains iodine is injected into the blood during a CT scan. The dye makes blood vessels and certain structures or organs inside the body more visible on the CT scan pictures. This process helps in evaluating blood flow, detecting some types of tumors, and locating inflammation. Contrast material is often used to obtain images of the chest, abdomen, and pelvis. If an abdominal CT scan is done, a contrast material is usually given by mouth (orally).

Purpose of a CT
CT scans are used to study many areas of the body, including:

• Chest and thorax. A CT scan can detect an infection, detect tumors in the spaces between the lungs, help determine whether lumps in the lungs are cancerous, detect a bulge in a blood vessel (aneurysm), and help determine whether cancer has spread into the chest from other locations in the body.
• Abdomen. A CT scan can detect an abnormal collection of fluid (such as a cyst or abscess), tumors, a bulge in a blood vessel (aneurysm), enlarged lymph nodes, foreign objects, and bleeding into the abdominal cavity. It can also help determine if cancer has spread from another place in the body to abdominal organs or lymph nodes.
• Urinary tract. A CT scan can detect kidney stones, blockage, abnormal growths, infection, structural problems, and some diseases of the urinary tract.
• Liver. A CT scan can detect liver tumors, bleeding from the liver, and some liver diseases. It can also help determine the cause of a yellow tint in the skin and eyes (jaundice).
• Pancreas. A CT scan can detect a tumor in the pancreas or inflammation of the pancreas (pancreatitis).
• Gallbladder and bile ducts. A CT scan can be used to investigate blockage of the bile ducts. Gallstones occasionally show up on a CT scan, but an ultrasound test is usually used to detect gallstones.
• Adrenal glands. A CT scan can detect tumors in the adrenal glands.
• Spleen. A CT scan can be used to evaluate injury to the spleen.
• Spine and spinal bones (vertebrae). A CT scan can detect tumors, injuries, deformities, narrowing of the spinal canal (spinal stenosis), and other problems of the spine. The test can also identify a ruptured (herniated) disc of the spine and help determine if thinning of the bones (osteoporosis) is severe and affecting the spine.

How to Prepare
Before the CT scan, tell your doctor if:

• You might be pregnant.
• You become very uneasy in small, confined spaces. You need to remain immobile inside the CT scanner, so a medication to relax may be needed. However, this is typically not a problem since the cylinder within the scanner is short and doesn't confine much of your body.
• You are allergic to shellfish (shrimp, scallops, lobster), the iodine dye used as contrast material, or any substance with iodine. You should also tell your doctor if you have asthma, are allergic to any medications, or have ever had a serious allergic reaction to any substance like the venom from a bee sting. Within the past 4 days, you have had an X-ray test using barium contrast material (such as a barium enema) or have taken a medication (such as Pepto-Bismol) that contains bismuth.

If you will be given an injection of contrast material, you may need to avoid eating and drinking for 4 hours before the test.

How It Is Done
A CT scan is usually done by a radiology technologist. The resulting pictures are usually interpreted by a doctor who specializes in evaluating X-rays (radiologist). However, some other types of doctors (such as a surgeon or an internal medicine doctor) may review a CT scan to help guide a person's care.

You will need to remove jewelry that might interfere with the X-ray picture. You will need to take off all or most of your clothes, depending on which area is examined (you may be allowed to keep on your underwear if it does not interfere with the test). You will be given a cloth or paper covering to use during the test.

During the test, you will lie on your back on a table that is attached to the CT scanner. The scanner is a large square machine with a circular opening that contains the X-ray tube and detector.

The table will slide into the hole in the scanner while a cylinder lining the hole rotates around your body. The table will move a small distance every few seconds to reposition you for each new "slice" of the CT scan. You may hear clicking or buzzing sounds as the table moves and the cylinder turns.

It is very important to hold completely still while your body is being scanned. Otherwise, repeat scans may be needed.

During the test, you are usually alone in the scanner room. However, the technologist will watch you through an observation window, and you will be able to communicate through an intercom.

If contrast material is needed, it will be injected into a vein (usually in your arm). For a CT scan of the intestines, the contrast material is usually given by mouth. An enema using contrast material is also done occasionally. CT scans may be done before and after the contrast material is given.

A CT scan usually takes 30 to 90 minutes, but because of delays that can occur you should allow at least 2 hours.

How It Feels
You will feel no discomfort from the scan itself or from the X-rays. However, the table you lie on may feel hard and the room may be chilly because air-conditioning helps to keep the equipment at a constant temperature. You may become uncomfortable from lying in one position for a long time.

Some people unease (claustrophobia) when inside the CT scanner. If so, you may be administered a sedative to better relax.

If contrast material is injected, you may feel warm and flushed and get a metallic taste in your mouth. In rare instances, the contrast material may cause nausea, vomiting, or a headache. If you develop these symptoms, tell the technologist or your doctor.

Risks
A CT scan has a small risk of causing a problem:

• There is slight risk of developing an allergic reaction to the iodine contrast material. The reaction can be mild (itching, rash) or severe (difficulty breathing or sudden shock). Death resulting from an allergic reaction is rare. Medications can be used to control most reactions. Be sure to tell your doctor if you have allergies of any kind (such as hay fever, iodine allergy, eczema, hives, or food allergies).
• The contrast material can cause water loss or direct damage to the kidneys that may lead to kidney failure. This is a special concern for people who have kidney problems, diabetes, or dehydration. Special precautions are taken during the test to prevent problems for people with these conditions.
• There is always a slight risk of damage from being exposed to any radiation. However, our modern technologies have reduced that low risk even further, especially compared to the potential benefit from such tests.

Results
The radiologist may discuss preliminary results immediately following completion. However, you can usually expect the final results to take about 48 hours to allow for detailed analysis.