"Recently, a human MRI instrument has been constructed which operates at a field strength of 8 tesla, or 160,000 times the earth’s magnetic field at sea level. At the heart of this MRI scanner is an 8 tesla/80 cm solenoidal magnet which is manufactured from 414 km (257 miles) of copper imbedded niobium-titanium superconducting wire wound on four aluminum formers. This results in a total inductance of 4155 henries. The four aluminum formers are enclosed in a helium dewar which can hold 1,600 liters of liquid helium. The helium dewar is positioned within a vacuum jacket and an aluminum magnet casing. The assembled magnet weighs approximately 35,000 Kg (77,000 lbs), operates at 4 KO (-452OF), and carries 198 amperes of current once fully energized. As such, it contains a phenomenal 81.5 Mjoules of stored persistent magnetic energy. It is believed that this currently represents the most stored magnetic energy in the world for all types of magnets. The inner windings of this magnet are designed to operate at 21,000 p.s.i of force. The magnet is characterized with a homogeneity of 5 ppm over a 40 cm central volume. In order to contain the large stray magnetic field from this magnet, it is housed in a magnetically shielded room. The walls of this room are made from 30.5 cm (12 inches) 1030 steel plate and the ceilings and floor are made from 15.2 cm (6 inches) steel plate resulting in a total shield weight of more than 200 tons (nearly 500,000 lbs). In addition to the magnet itself, the 8 tesla MRI is comprised of radiofrequency amplifiers which are able to deliver up to a total of 10 kwatts of power at frequencies up to 340 MHz, the operational proton frequency of the scanner."
P.-M. L. Robitaille, 2000 Yearbook of Science and Technology.