What is magnetic resonance imaging (MRI), and how does it work?

MRI is a structural and functional imaging technique that uses magnetism and radiofrequency (RF) waves to create tomographic (cross-sectional) images. A patient is placed into a scanner that contains a magnet that generates a very strong magnetic field.

Atomic nuclei in the body, such as of hydrogen atoms, have a net magnetic moment and act like tiny magnets, aligning themselves with the main magnetic field. RF waves are turned on to knock the nuclear magnetic moments out of alignment. When the RF waves are then turned off, the nuclei realign themselves (i.e., relax) in the direction of the main magnetic field although at differential rates in different tissues. These differential relaxation rates lead to different signal properties of tissues that are detected by an RF coil placed around the patient. Magnetic gradients, controlled linear alterations of the magnetic field over distance in prespecified directions, are utilized to spatially localize the tissue signals so that MR images can be created. The process by which atomic nuclei undergo absorption or emission of RF energy is known as nuclear magnetic resonance (NMR).

When was MRI developed?

Isidor Rabi discovered the phenomenon of nuclear magnetic resonance in 1938 and received the Nobel Prize in Physics in 1944. Raymond Damadian discovered that the NMR signals of cancers appear different from those of normal tissues in 1971, proposed the concept of (and filed a patent for) the use of NMR for detecting cancer in the human body in 1972, and was the first to perform a human body MRI scan with the first full-body MRI scanner in 1977. In 1973, Paul Lauterbur produced the first tomographic MR image, and in 1976, Sir Peter Mansfield produced the first tomographic MR image of a human’s finger. Lauterbur and Mansfield received the Nobel Prize in Physiology or Medicine in 2003.


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