What Is the Difference Between a MRI and a PET Scan?

A magnetic resonance imaging, or MRI, machine surrounds the patient with a magnetic field and emits radio waves to generate cross-sectional images, according to Mayo Clinic. A positron emission tomography, or PET, scanner detects radioactivity in the body after the patient is given a special radioactive tracer chemical.

Both MRI and PET procedures require lying on a table that slides into a tube-like scanner. However, radiologists typically use MRI scans to capture detailed images of an organ's size and appearance, while PET scans help them determine whether the organs are functioning properly, Medical News Today notes.

MRI technology produces high-resolution images, giving radiologists noninvasive methods for observing abnormalities, such as spinal cord damage or tumors, Mayo Clinic states. When a patient enters the MRI machine, an intense concentration of magnetic energy causes the body's hydrogen atoms to align. Targeted radio waves cause the atoms to give off energy signals, which the computer uses to create visual representations of the body's interior. MRI scans may pose safety risks for individuals with implanted metal devices, such artificial heart valves.

PET scans are valuable for locating organ damage, but limited exposure to radiation makes the procedure unsafe for pregnant women, according to Medical News Today. To create a radioactive environment within the body, a radiologist gives the patient a safe dosage of a radionuclide, a drug combined with a natural tracer substance, such as water. The scanner detects the positive energy particles given off by the radionuclide as it travels through the body.