OverviewComputed tomography (CT) is a computer-aided x-ray technique. X-rays consist of electromagnetic waves of energy. They penetrate the body to varying extents depending upon the density of the structures being viewed. The result is black and white images of interior portions of the body. A CT scan produces detailed cross-sectional views of the body, similar to slices of bread.
The technology behind CT scans has advanced rapidly in recent years. Older machinery used to take minutes to obtain enough information for a single "slice." Now, the same image can be produced in seconds. Newer scanners called spiral or helical scanners are so fast that they can scan the entire chest during one held breath. These devices can also produce three-dimensional scans.
Who is a candidate for the test?CT scans are performed to evaluate:
• abnormalities that showed up on other other types of x-rays
• injuries
• tumors that are suspected to represent cancer. CT scans can determine how much some cancers have spread or metastasized and can monitor the effectivness of treatment.
• bony abnormalities
• brain abnormalities
• abdominal symptoms. Use of CT scans in these cases can often prevent exploratory surgery.
• suspicious chest abnormalities
CT scans are also used to guide needles when taking tissue samples. In addition, the technique is useful in gauging a person's recovery after an operation. CT scans can also be used to guide instruments for surgery deep in the brain.
How is the test performed?A person having a CT scan will need to undress and put on an exam gown. Next, the person will lie on a narrow table. The table will slide through a machine called a gantry, that looks like a donut. While in the gantry, an x-ray tube travels around the individual creating computer-generated x-ray images.
Some types of exams require the individual to receive an intravenous injection of iodinated contrast, which is a dye that makes some tissues show up better. Scans of the intestines sometimes call for the person to drink diluted iodinated contrast solution prior to the exam. After the exam, the technologist will view the pictures. If they are adequate, the person is free to leave.
What is involved in preparation for the test?
A person having the test will be asked to refrain from eating or drinking for 4 hours before the scan. All jewelry and metal objects that may interfere with the exam need to be removed beforehand, as well.
What do the test results mean?
A CT scan provides a direct image of soft tissue structures such as the, liver, lung, spleen, pancreas, lymph nodes and fatty tissues. CT is also helpful for identifying and tracking large abnormalities such as tumors.
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