MR scanner magnets are made of four types of electromagnetic windings: 1) The main magnet, made of superconducting material, creates a variable magnetic field; 2) X coil, made of a resistive material, creates a variable magnetic field, horizontally, from left to right, across scanning tube; 3) Y coil creates varaing magnetic field, vertically, from botom to top; 4) Z coil creates varaing magnetic field, longitudinally, from head to toe, within scanning tube.
Superconductors, which create the main magnetic field, should be cooled by liquid helium and liquid nitrogen.
The superconductors used exclusively are: niobium-titanium (NbTi), niobium-tin (Nb3Sn), vanadium-gallium (V3Ga) and magnesium-diboride (MgB2). Only magnesium diboride is a high temperature superconductor, with a critical temperature Tc = 390K. The three remaining superconductors are low temperature.