Magnetic resonance imaging (MRI), or Nuclear magnetic resonance imaging (NMRI), is primarily a medical imaging technique most commonly used in radiology to visualize the structure and function of the body.
MRI is a relatively new technology, which has been in use for little more than 30 years (compared with over 110 years for X-ray radiography).
Magnetic resonance imaging was developed from knowledge gained in the study of nuclear magnetic resonance.
How MRI works
When a person lies in a scanner, the hydrogen nuclei (i.e., protons) found in abundance in the human body in water molecules, align with the strong main magnetic field. A second electromagnetic field, which oscillates at radiofrequencies and is perpendicular to the main field, is then pulsed to push a proportion of the protons out of alignment with the main field. These protons then drift back into alignment with the main field, emitting a detectable radiofrequency signal as they do so.
Contrast agents may be injected intravenously to enhance the appearance of blood vessels, tumors or inflammation.
Contrast agents may also be directly injected into a joint, in the case of arthrograms, MR images of joints.
MRI is used to image every part of the body, but is particularly useful in neurological conditions, disorders of the muscles and joints, for evaluating tumors and showing abnormalities in the heart and blood vessels.
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