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FAQ: Radiation Risk From Medical Imaging

What You Need to Know About Radiation Risks From CT, Other Scans
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WebMD Health News
Reviewed by Laura J. Martin, MD

March 31, 2010 -- In a sometimes contentious two-day meeting, the FDA has put forward its plan to reduce unnecessary radiation exposure from CT scans, nuclear medicine studies, and fluoroscopy.

These medical imaging techniques represent only about a fourth of imaging tests that expose U.S. patients to radiation, but they expose patients to nearly 90% of the radiation they get from medical imaging.

And more and more Americans get these tests every year. They're the main reason why the U.S. population's radiation exposure has almost doubled over the last 20 years.

An individual's chance of getting cancer from a single scan is small. But because the scans are so widely used, they cause a considerable amount of harm. One study estimated that the CT scans performed in 2007 are related to some 29,000 future cancers.

What are these tests? What are their risks? When do the tests' benefits outweigh their risks? Here are WebMD's answers to these and other questions.

What are CT scans, nuclear medicine studies, and fluoroscopy?

In a normal X-ray, a person gets a blast of radiation that creates an image on a two-dimensional square of film.

During a computed tomography or CT scan (sometimes called a CAT scan), a rotating device shoots X-rays through the body to produce several cross-sectional images. A computer assembles these images into a 3-D image of the inside of the body. Scans that take more images -- and expose the patient to more radiation -- yield sharper images.

During nuclear medicine studies, such as positron emission tomography or PET scans, the patient is given a small amount of a radioactive substance. A detector then views an image of this "radiotracer" as it moves through the body.

During fluoroscopy, a device passes continuous X-rays through the body to yield a real-time moving image.

How much radiation does a person get from medical imaging studies?

Getting a CT scan gives a patient as much radiation as 100 to 800 chest X-rays.

Getting a nuclear medicine study exposes a patient to as much radiation as 10 to 2,050 chest X-rays.

Getting a fluoroscopic procedure exposes a patient to as much radiation as 250 to 3,500 chest X-rays.

For perspective, a person gets the equivalent of one chest X-ray from normal background radiation in about two and a half days. In 2.7 years, people get as much radiation just from being on the planet as they do from an abdominal CT scan.

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