Thoracic CT (computed tomography) is an imaging method that uses x-rays to create cross-sectional pictures of the chest and upper abdomen.
Chest CT; CT scan - lungs; CT scan - chest
How the Test is Performed
The test is done in the following way:
- You may be asked to change into a hospital gown.
- You lie on a narrow table that slides into the center of the scanner. Once you are inside the scanner, the machine's x-ray beam rotates around you.
- You must be still during the exam, because movement causes blurred images. You may be told to hold your breath for short periods of time.
The complete scan takes 30 seconds to a few minutes.
Certain CT scans require a special dye, called contrast, to be delivered into the body before the test starts. Contrast highlights specific areas inside the body and creates a clearer image. If your doctor requests a CT scan with intravenous contrast, you will be given it through a vein (IV) in your arm or hand. A blood test to measure your kidney function may be done before the test. This test is to make sure your kidneys are healthy enough to filter the contrast.
How to Prepare for the Test
Some people have allergies to IV contrast and may need to take medications before their test to safely receive this substance.
Contrast can be given in several ways, depending on the type of CT being performed.
- It may be delivered through a vein (IV) in your hand or forearm.
- It may be given through the rectum using an enema.
- You might drink the contrast before your scan. When you actually drink the contrast depends on the type of exam being done. The contrast liquid may taste chalky, although some are flavored to make them taste a little better. The contrast eventually passes out of your body through your stool.
If contrast is used, you may also be asked not to eat or drink anything for 4 to 6 hours before the test.
If you weigh more than 300 pounds, have your doctor contact the scanner operator before the exam. CT scanners have a weight limit. Too much weight can damage the scanner's working parts.
Because it is hard for x-rays to pass through metal, you will be asked to remove jewelry and wear a hospital gown during the study.
How the Test will Feel
Some people may have discomfort from lying on the hard table.
Contrast given through an IV may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.
There is no recovery time, unless you were given medicine to relax. After a CT scan, you can go back to your normal diet, activity, and medications.
Why the Test is Performed
CT quickly creates detailed pictures of the body. The test may be used to get a better view of the structures inside the chest.
A thoracic CT may be done:
- After a chest injury
- When a tumor or mass (clump of cells) is suspected, including a solitary pulmonary nodule seen on a chest x-ray
- To determine the size, shape, and position of organs in the chest and upper abdomen
- To look for bleeding or fluid collections in the lungs or other areas
- To look for infection or inflammation in the chest
- To look for blood clots in the lungs
What Abnormal Results Mean
Thoracic CT may show many disorders of the heart, lungs, or chest area, including:
- Abnormalities of the blood vessels in the lungs
- Aortic aneurysm (in the chest area)
- Buildup of blood or fluid
- Collection of fluid around the lungs (pleural effusion)
- Damage to, and widening of the large airways of the lungs (bronchiectasis)
- Enlarged lymph nodes (lymphadenopathy)
- The stage of some lung tumors or esophageal cancer
- Tumors, nodules, or cysts in the chest
Other conditions under which the test may be performed:
- Alcoholic cardiomyopathy
- Atrial myxoma
- Cardiac tamponade
- Coarctation of the aorta
- Dilated cardiomyopathy
- Heart failure
- Hypertensive heart disease
- Idiopathic cardiomyopathy
- Infective endocarditis
- Ischemic cardiomyopathy
- Left-sided heart failure
- Mesothelioma (malignant)
- Metastatic cancer to the lung
- Mitral regurgitation; acute
- Mitral regurgitation; chronic
- Mitral valve prolapse
- Pericarditis; bacterial
- Pericarditis; constrictive
- Pericarditis; post-MI
- Peripartum cardiomyopathy
- Pulmonary edema
- Restrictive cardiomyopathy
- Senile cardiac amyloid
- Superior vena cava obstruction
CT scans and other x-rays are strictly monitored and controlled to make sure they use the least amount of radiation. CT scans use low levels of ionizing radiation, which has the potential to cause cancer and other defects. However, the risk from any one scan is small. The risk increases as many more studies are done.
In some cases, a CT scan may still be done if the benefits greatly outweigh the risks. For example, it can be more risky to not have the exam if your doctor thinks you might have cancer.
The most common type of contrast given into a vein contains iodine. If a person with an iodine allergy is given this type of contrast, nausea, sneezing, vomiting, itching, or hives may occur. In rare cases, the dye can cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, you should notify the scanner operator immediately. Scanners come with an intercom and speakers, so the operator can hear you at all times.
In people with kidney problems, the dye may have harmful effects on the kidneys. In these situations, special steps may be taken to make the CT scan safer.
A CT scan is one of the best ways of looking at soft tissues such as the heart and lungs.
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Stark P. Imaging in pulmonary disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 84.