magnetic resonance imaging
- magnetic resonance imaging
-
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.
MRI images can be constructed in any plane, and the technique is particularly valuable in studying the
brain and
spinal cord. It reveals the precise extent of tumours (
tumour) rapidly and vividly, and it provides early evidence of potential damage from
stroke, allowing physicians to administer proper treatments early. Refinement of the magnetic fields used in MRI has led to the development of highly sensitive imaging techniques, such as diffusion MRI and functional MRI (
functional magnetic resonance imaging), that are designed to image very specific properties of tissues. As with MRI, these techniques have helped revolutionize biomedical research and
diagnosis.
See also magnetic resonance.
* * *
Universalium.
2010.
Look at other dictionaries:
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