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Introduction

•CT or CAT scans are special x-ray tests that produce cross-sectional images of the body using x-rays and a computer. These images allow the radiologist, a medical doctor who specializes in images of the body, to look at the inside of the body just as you would look at the inside of a loaf of bread by slicing it. This type of special x-ray, in a sense, takes "pictures" of slices of the body so doctors can look right at the area of interest. CT scans are frequently used to evaluate the brain, neck, spine, chest, abdomen, pelvis, and sinuses.

•CT has become a commonly performed procedure. Scanners are found not only in hospital x-ray departments, but also in outpatient offices.
•CT has revolutionized medicine because it allows doctors to see diseases that, in the past, could often only be found at surgery or at autopsy. CT is noninvasive, safe, and well-tolerated. It provides a highly detailed look at many different parts of the body.

•If you are looking at a standard x-ray image or radiograph (such as a chest x-ray), it appears as if you are looking through the body. CT and MRI are similar to each other, but provide a different view of the body than an x-ray does. CT and MRI produce cross-sectional images that appear to open the body up, allowing the doctor to look at it from the inside. MRI uses a magnetic field and radio waves to produce images, while CT uses x-rays to produce images. Plain x-rays are an inexpensive, quick exam and are accurate at diagnosing things such as pneumonia, arthritis, and fractures. CT and MRI better evaluate soft tissues such as the brain, liver, and abdominal organs, as well as look for subtle abnormalities that may not be apparent on regular x-rays.

•People often have CT scans to further look at an abnormality seen on another test such as an x-ray or an ultrasound. They may also have a CT to check for specific symptoms such as pain or dizziness. People with cancer may have a CT to look for the spread of disease.
•A head or brain CT examines the various structures of the brain to look for a mass, stroke, area of bleeding, or blood vessel abnormality. It is also sometimes used to look at the skull.
•A neck CT checks the soft tissues of the neck and is frequently used to study a lump or mass in the neck or to look for enlarged lymph nodes or glands.
•CT of the chest is frequently used to further study an abnormality on a plain chest x-ray. It is also often used to look for enlarged lymph nodes.

chest x-ray. It is also often used to look for enlarged lymph nodes.
•Abdominal and pelvic CT looks at the abdominal and pelvic organs (such as the liver, spleen, kidneys, pancreas, and adrenal glands) and the gastrointestinal tract. These studies are often ordered to check for a cause of pain and sometimes to follow up on an abnormality seen on another test such as an ultrasound.

•A sinus CT exam is used to both diagnose sinus disease and to look for a narrowing or obstruction in the sinus drainage pathway.
•A spine CT test is most commonly used to look for a herniated disc or narrowing of the spinal canal (spinal stenosis) in people with neck, arm, back, and/or leg pain. It is also used to look for a fracture or break in the spine.

Risks
CT is a very low-risk procedure.

•You will be exposed to radiation when undergoing a CT. However, it is a safe level.
•The biggest potential risk is if you need to get a contrast (also called dye) injection. This can help distinguish normal tissues from abnormal tissues. It also helps to distinguish blood vessels from other structures such as lymph nodes.

•Like any medication, some people can have a bad reaction to the contrast. The chance of a fatal reaction to the contrast is about 1 in 100,000. Those at increased risk may require special pretreatment and should have the test in a hospital setting. Anyone who has had a prior contrast reaction or severe allergic reaction to other medications, has asthma or emphysema, or has severe heart disease is at increased risk for a contrast reaction and is referred to a hospital x-ray department for the exam.

•Any time an injection is done into a vein, there is a risk of the contrast leaking outside of the vein under the skin. If a large amount of contrast leaks under the skin, in rare cases, this can cause the skin to break down.

CT Scan Preparation
If you are to have a contrast injection, you should not have anything to eat or drink for a few hours before your CT scan because the injection may cause stomach upset. To receive the contrast injection, an IV is inserted into your arm just prior to the scan. The contrast then enters your body through the IV.

Prior to most CT scans of the abdomen and pelvis, it is important to drink an oral contrast agent that contains dilute barium. This contrast agent helps the radiologist identify the gastrointestinal tract (stomach, small and large bowel), detect abnormalities of these organs, and to separate these structures from other structures within the abdomen. You will be asked to drink slightly less than a quart spread out over 1.5-2 hours.

During the Procedure
Most CT scans are conducted as an outpatient procedure. You have the test and then go home.

•The CT scanner looks like a large donut with a narrow table in the middle. Unlike MRI, in which you would be placed inside the tunnel of the scanner, when undergoing a CT, you rarely experience claustrophobia because of the openness of the doughnut shape of the scanner. Typically you lie on your back on the table, which moves through the center of the machine. You move through the scanner either head first or feet first, depending on the part of the body being scanned. For certain scans such as sinuses and middle ear, you would lie on your stomach and go through head first.

•You must remain motionless for the length of the study, which is typically just a few minutes. The entire procedure, which includes set-up, the scan itself, checking the pictures, and removing the IV if needed, takes 15-45 minutes depending on what part of the body is being scanned.


◦For some studies, you will be asked to hold your breath for up to 20 seconds.


◦No metal may be worn.


◦What clothing you wear depends on the nature of the study. For a CT of the chest, abdomen, or pelvis, for example, usually you will change into a hospital gown. For a head CT, you can wear normal street clothes.


◦Sedation is rarely necessary. The machine is quiet, so all you hear during the test is a quiet whirr.


◦The technologist is in the next room and can observe you through a large window.

After the Procedure
If you received a contrast injection, the IV is removed from your arm before you go home. There should be no effects from the scan or the contrast injection. In the rare circumstance that you received sedation, you will be sent home once you are awake and alert. Someone will have to drive you home

Your CT scan is interpreted by a radiologist, a medical doctor trained to interpret various x-ray studies. The results are sent to your doctor. How soon your doctor receives the report depends on the imaging center where the study is performed

When to Seek Medical Care
The reaction to the contrast is almost always immediate, so it is very rare to have a reaction after you leave the facility. However, if you think you are having a delayed reaction to the contrast, call the facility where you had the exam.

Symptoms include itching and difficulty breathing or swallowing. If contrast leaked under the skin, you should look for increased redness, swelling, or pain. You will often be asked to come back the next day so your skin can be checked. There are no side effects to the exam itself.

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 takes less than a second and 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.

An iodine dye (contrast material) is often used to make structures and organs easier to see on the CT pictures. The dye may be used to check blood flow, find tumors, and look for other problems. The dye can be used in different ways. 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. CT pictures may be taken before and after the dye is used.

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.

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.

Chest (thorax). A CT scan of the chest can look for problems with the lungs, heart, esophagus, 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 cysts, abscesses, infection, tumors, an aneurysm, enlarged lymph nodes, foreign objects, bleeding in the belly, diverticulitis, inflammatory bowel disease, and appendicitis.

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. See a picture of a CT of diseased kidneys . 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.