What Are the Differences Between a CAT Scan, a PET Scan and an MRI?


Quick Answer

The U.S. National Library of Medicine describes that a positron emission tomography, or PET scan, shows how organs and tissues are working, while a magnetic resonance image, an MRI, and a computed tomography, a CT scan, show blood flow to and from organs.

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Full Answer

The Library of Medicine describes a PET scan as using a small amount of radioactive material, called a tracer. The tracer absorbs into the body and gives the radiologist a well defined, three-dimensional picture. Tracers are absorbed within an hour and leave the body within two to eight hours. A PET scan uses about as much radiation as a routine CT scan.

CT scans use a spiraling, x-ray beam that rotates around the patient to create two-dimensional pictures called "slices." These slices can be layered to create a three-dimensional image. A CT scan might require the use of a dye called "contrast." This dye could be administered three ways: orally, intravenously or into the rectum through an enema.

MRI machines use a large magnet and radio waves. The University of California San Francisco's Department of Radiology and Biomedical Imaging, describe an MRI as being slower but more detailed than a CT scan.

For all three tests, the patient is asked to lie down on a narrow table that slides into the imagining machine.

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