Differences Between a PET Scan, CAT Scan and MRI Scan

Updated July 20, 2017

A Positron Emission Tomography (PET) scan, Computerized Axial Tomography (CAT or CT) scan and Magnetic Resonance Imaging (MRI) scan are all tests used to diagnose and help treat patients who have medical conditions. According to the eMedicineHealth website, the MRI was developed in 1946 and the CAT scan was invented in 1974. The PET scan was developed in the early 1950s, according to

PET Scan

A PET scan is a type of imaging that uses nuclear medicine. This type of scan measures important body functions so doctors can see if the organs and tissues in the body are functioning properly. This includes blood flow, oxygen use and sugar metabolism.

Doctors use PET scans to detect cancer, determine blood flow to the heart and evaluate brain abnormalities. It is performed on an outpatient basis and usually takes about 30 minutes. The process of a PET scan involves a dose of radiotracer, which is injected, swallowed or inhaled by the patient. Once the radiotracer works its way through the body, the patient is moved into a scanner. The patient will be given a CAT scan first, then a PET scan, according to the RadiologyInfo website.

CAT scan

The CAT scan is a test that doctors use to diagnose and treat medical conditions. The CAT scan X-rays a patient's body to produce images that allow doctors to see internal organs, bones, soft tissue and blood vessels.

CAT scans are used for a variety of reasons. Some doctors prefer using this method to diagnose different forms of cancer, vascular diseases and spinal problems. During a CAT scan, x-ray beams and electronic x-ray detectors rotate around the person, measuring the amount of radiation that is absorbed throughout the body. A computer processes these images as the examination tables moves to get a cross-section x-ray of the entire body. The scan takes about 30 minutes.


An MRI uses a magnetic field, radio frequency pulses and a computer to produce detailed pictures of organs, bones and any internal body structure, which allows doctors to determine if there are diseases in the body.

An MRI is often used to evaluate organs, blood vessels and breasts to diagnose and monitor tumours, heart problems, diseases and breast cancer. The test does not use ionising radiation, but it instead uses radio waves that redirect the axes of spinning protons. During the exam, the patient is placed on an exam table with small devices around the body that will send and receive the radio waves. Sometimes a contrast material will be used in the exam through an IV. A series of images will be taken during the exam, which lasts about 15 to 45 minutes depending on what the exam is for.

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About the Author

Sharon Foss has been writing professionally since 2000. She has written for various media venues including and She holds a Bachelor of Arts in mass communication, specializing in print journalism, from Illinois State University.