MRI scanners come in a wide range of varieties consisting of the use of a variety of parts. The most common type of magnet used today is a superconducting magnet. The superconducting magnets generate a magnetic field by running current through a loop of wire. The loops of wire are surrounded by liquid helium that acts as a coolant. To prevent variations in temperature, multiple vacuum shields surround the coolant. The coolant is used to drop the temperature of the wire to 4 Kelvin, causing the wire to loose its resistance. As result, once passing current in the loop of wire energizes the system, it won't lose its magnetic field. The magnetic fields generated with superconducting magnets can range from 1.5 Tesla (for clinical applications) to 12 Tesla.