Patients are composed of approximately one to two-thirds water, depending on age and gender. The hydrogen atoms (protons of water), as well as the protons in the solid portions of the tissues, are tiny magnets whose properties are exploited in magnetic resonance imaging (MRI) for imaging:
Patients are placed in a very strong magnetic field (currently 1.5 tesla, about 15,000 times stronger than the Earth’s magnetic field) so that their protons spin predominantly in one direction. Then their protons are vibrated with a radio signal so that they in turn emit radio signals that are measured by antennas (called coils that are placed on the body). These signals are converted into slice images by the computer.
Magnetic resonance imaging is performed without X-rays and can therefore be used without hesitation in children and – for special questions – also in pregnant women. Occasionally, contrast medium (gadolinium) is required to differentiate between individual structures and between healthy and diseased tissue. Adverse side effects occur much less frequently compared to contrast agents used in computed tomography.