three-dimensional diagnostic imaging technique used to visualize organs and structures inside the body without the need for X-rays (X-ray) or other radiation. Magnetic resonance imaging (MRI) is valuable for providing detailed anatomical images and can reveal minute changes that occur over time. MRIs can be used to detect structural abnormalities that appear in the course of a disease, as well as how these abnormalities affect subsequent development and how their progression correlates with mental and emotional aspects of a disorder. Since MRI poorly visualizes bone, excellent images of the intracranial and intraspinal contents are produced.

During the 15-minute MRI procedure, a patient lies inside a massive hollow cylindrical magnet and is exposed to a powerful, steady magnetic field. Different atoms (atom) in the portion of the body being scanned resonate to different frequencies of magnetic fields. In MRI a background magnetic field lines up all the atoms in the brain. A second magnetic field, oriented differently from the background field, is turned on and off many times per second; at certain pulse rates, particular atoms resonate and line up with this second field. When the second field is turned off, the atoms that were lined up with it swing back to align with the background field. As they swing back, they create a signal that can be picked up and converted into an image. Tissue that contains a lot of water and fat produces a bright image; tissue that contains little or no water (e.g., bone) appears black.