Superconducting magnets are electromagnets that are partially built from superconducting materials and therefore reach much higher magnetic field intensity.
The coil windings of superconducting magnets are made of wires of a type 2 superconductor (mostly used is niobium-titanium - up to 15 Tesla the critical temperature is less then 10 Kelvin). These coils have no resistance when operated at temperatures near absolute zero (-273.15°C, -459°F, 0 K).
Liquid helium (4.2 K) is commonly used as a coolant (sometimes in addition with a second cryogen liquid nitrogen as an intermediate thermal shield to reduce the boil-off rate of liquid helium), which consequently conclude refilling (intervals: liquid helium ~ 3 month, liquid nitrogen ~ 2 weeks). There are cryogen-free superconducting magnets with a closed-cycle refrigerating system at the horizon. Superconducting magnets typically exhibit field strengths of greater than 0.5 T, operate clinically up to 3 T, and have a horizontal field orientation, which makes them prone to missile effects without significant magnetic shielding.
See also Quenching.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'

Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterized by the complete absence of electrical resistance and the damping of the interior magnetic field. A ideal superconductor can carry an electrical current without experiencing energy losses (resistance, heat). The resistance of superconducting wire is nearly equal to zero at temperature near to absolute zero (-273.15° C or 0 K). This temperature is usually established by using liquid helium.

See also Superconducting Magnet, and Cryogen.

(T) The SI unit of magnetic flux density.
Definition: 1 T is the field intensity generating 1 newton of force per ampere of current per meter of conductor. The tesla unit value is defined as a field strength of 1 weber per square meter of area, where 1 weber represents 1 x 108 (100 000 000) flux lines.
One T is equal to 10 000 gauss, the older (CGS) unit. A field of 1 tesla is quite strong, the Earth's magnetic flux density, at its surface, is about 50 microteslas (μT). The slew rate of MRI devices is measured in mT/m/msec or T/m/sec.