6. Devices generating a fixed or variable magnetic field

6.1 Magnetic resonance imaging (MRI)

MRI produced its first images in the 1970s, and expanded rapidly from the 1980s onwards. It enables many organs to be studied with great precision by producing cross-sectional images in different planes, and reconstructing the analyzed structure in three dimensions. The machine consists of a cylinder in which an intense magnetic field is created, and into which the examination bed is inserted.

The magnetic field is created by magnets or a superconducting coil. Some of the most recent machines use magnets with a total mass in excess of one tonne to generate the magnetic field. Nd-Fe-B magnets are generally the preferred choice, in order to obtain high fields that are as constant as possible over a large volume. Two geometric...