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Scanning systems that use strong magnetic fields, radio-frequency (RF) radiation, and computerized processes to translate hydrogen nuclei distribution (some systems can translate other nuclei exhibiting nuclear magnetic resonance) in body tissue into images of anatomic structures. Following exposure to high magnetic and RF fields, body-tissue nuclei emit low-power RF signals that are detected by the system RF receiver. The computer uses these RF data to construct an image of the exposed tissue. Magnetic resonance imaging (MRI) systems consist of a primary magnet (resistive, superconductive, or permanent); gradient magnets; an RF subsystem, including an RF transmitter/receiver and coils; a patient table; a computer subsystem, including software for image processing, display monitors, and a data storage unit; and an operator console. MRI scanning systems are used to obtain high-resolution images with good contrast of tissues without using ionizing radiation. Most of these systems are used to distinguish normal from diseased tissue and to diagnose and track the progress and treatment of diseases (e.g., cancer, brain edema, iron storage).
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