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Doctor Decoded: CT Scan vs. MRI

Learn the difference between CT scans and MRIs, including the type of energy they use and what they’re used for.

Lauren SmithPreeti Parikh, MD
Written by Lauren Smith | Reviewed by Preeti Parikh, MD
Updated on January 13, 2021

Raise your hand if you have no idea what the difference between CT scans and MRIs are. Yeah, let’s face it: If you don’t work in health care, it’s easy to get these two imaging types mixed up.

CT Scans and MRIs: The Similarities

CT scans and MRIs do have a few things in common. Most notably, both scans typically require you to lie on a table that slowly slides into a round, tunnel-like machine. They both create incredible images of the body, albeit in different ways.

What Is a CT Scan?

CT scan stands for computed tomography scan. Like an X-ray, it uses radiation to create the image. However, CT scans are much more detailed than an X-ray, and they can create cross-sectional, 360-degree views of the body’s structures. That’s because the X-ray beam of a CT scan moves in a circle around the body.

Because of the fine detail of CT scans, they are great for diagnosing small fractures, blood clots, internal bleeding, and sometimes even signs of cancer or heart disease.

Doctors may perform CT scans “with or without contrast.” This refers to the use of a contrast dye that essentially helps light up certain parts of the body. For example, to see your gastrointestinal system, you might take the contrast dye by mouth. The CT scan can then get vivid pictures of the digestive tract as the dye moves through. You can also get the dye via injection to look at almost any organ or tissue.

What Is an MRI?

MRI stands for magnetic resonance imaging. Unlike a CT scan or X-ray, MRIs use a large, powerful magnet to create the images—not radiation. Essentially, the body’s protons react to the magnetic field, which creates signals that are picked up by the MRI receiver.

MRIs are particularly good at differentiating between tissue types. As a result, they’re useful for diagnosing problems with cartilage, ligaments, tendons, and muscles. They are also a common method for diagnosing subtle problems with the brain and spine. That said, MRIs can help doctors check on almost any organ.

Your medical history may play a role in your eligibility for an MRI. Most notably, people who have metal or electronic devices in their body, such as a cardiac pacemaker, should not receive MRIs due to the magnetic force.

Imaging may be improving and becoming more detailed, but don’t forget how impressive the original X-ray was (and still is). Check out the history of the X-ray here.

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