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How does magnetic resonance imaging use magnetic fields and radio waves?

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Learn about magnetic fields and the levels of particles, atoms, crystals, and domains — magnet Magnetic fields and the levels of magnetism of particles, atoms, crystals, and domains.

Magnetic resonance imaging (MRI) utilizes powerful magnetic fields and radio waves to create detailed, three-dimensional images of the body’s internal structures without using ionizing radiation.12

The process relies on the behavior of hydrogen nuclei (protons), which act like tiny magnets. The procedure functions through the following steps:13

Alignment: The patient is placed inside a large, hollow magnet that generates a strong, steady background magnetic field. This field causes the hydrogen nuclei in the body to align with it.13
Resonance: A second, oscillating magnetic field—delivered via radio waves—is applied at specific frequencies. This causes the hydrogen nuclei to absorb energy and shift their alignment.132
Signal Emission: When the radio frequency pulse is turned off, the nuclei return to their original alignment with the background field. As they do so, they emit radio signals.12
Imaging: A computer detects these signals and processes them to construct high-contrast images based on the density of hydrogen nuclei in different tissues.12

Because this technique relies on the magnetic properties of atoms, it is highly effective for visualizing soft tissues, though it is not suitable for patients with certain metal implants, such as pacemakers.13