Читать книгу Essentials of MRI Safety - Donald W. McRobbie - Страница 22

The magnet is the largest single component of the system. Most systems use superconducting magnets. Superconductivity is a quantum mechanical property whereby, below a critical temperature T_c, an electrical conductor loses its electrical resistance, enabling large electrical currents to be sustained in perpetuity without a driving voltage from a power supply. As long as the windings are kept sufficiently cold, the current and hence the magnet’s field persists indefinitely. Liquid helium with a boiling point of −269 °C (4.3 K or kelvin) is used for cooling. Safety consequences of this are considered in Chapter 12 .