What Is the Difference Between an MRI and PET Scan?

An MRI scan of the brain.
An MRI machine uses a magnetic field and radio waves to create pictures of internal organs and bone structures.
An MRI machine.
A medical professional reviewing an MRI.
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  • Written By: Erik J.J. Goserud
  • Edited By: PJP Schroeder
  • Last Modified Date: 16 August 2014
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The primary difference between an MRI and PET scan is the way in which each method conjures up the image that health providers rely on. These scans are incredibly valuable in confirming and exploring possible diagnoses, without which physicians and other professionals would be less able to effectively treat disease. Functionally, the both of these imaging studies act to penetrate peripheral structures in obtaining similar goals; however, their methods of doing so differ. Simply stated, an MRI uses magnetic technology, while a PET scan detects a substance in the body to produce an active image.

Both the MRI and PET scan are acronyms. MRI is an abbreviation for magnetic resonance imaging, while PET stands for positron emission tomography. Although both terms may be intimidating to the lay person, they truly are very descriptive of what each scan accomplishes and how it does so.

Magnetic resonance imaging uses multiple magnetic fields, each very strong, to physically align specific atoms in the internal structures of the body. These magnetic fields cause a rotational movement of the nuclei in the center of the atoms, and these variations are due to locational differences as well the type of atom. These disparities in rotational speed are recorded and translated to form a magnetic resonance image. This image generally reflects an internal structure of the body. One strength of MRIs is their ability to illustrate discrete differences in soft tissues, notably the brain, heart, muscles, and growths.


The MRI and PET scan differ mostly in modality. While the MRI uses magnetic fields, an active ingredient is the key for successful PET scanning. This substance is usually injected into a specific region of the body or ingested, and as this radio tracer decays, it emits positively charged particles, which are picked up up with specialized equipment. The differences in emission show how the body's systems are functioning. Functional differences may be expressed with differing brightnesses and colors on the computerized image.

It is important to realize that an MRI and PET scan differ fundamentally in the way they acquire their images as well as the circumstances under which they may be utilized. Taking and interpreting such images requires a great deal of knowledge, which is why only trained professionals should administer or draw conclusions from these tests. These tests are tremendously complicated procedures whose mechanical processes are only completely understood by those trained to do so.


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