Magnetic resonance imaging systems and methods

A magnetic resonance (MR) imaging system for measuring near metal comprising:

• a superconducting magnet for generating a main magnetic field;
• a power supply for providing a current for ramping the main magnetic field;
• a switch selectively connecting the superconducting magnet to the power supply and having an open state and a closed state, wherein when in the closed state the switch connects the superconducting magnet and the power supply in a connected circuit;
• a mechanical cryocooler in thermal contact with the superconducting magnet and operable to reduce and maintain a temperature of the superconducting magnet below a transition temperature of the superconducting magnet;
• a magnetic field controller programmed to ramp the main magnetic field from a first magnetic field strength to a second magnetic field strength by:
• setting a current generated by the power supply to an initial current value;
• activating the switch to its closed position, thereby connecting the superconducting magnet and the power supply in the connected circuit;
• adjusting the current generated by the power supply;
• and
• activating the switch to its open position when the second magnetic field strength is reached, thereby disconnecting the superconducting magnet and the power supply from the connected circuit and placing the superconducting magnet in a closed circuit;
• a gradient system positioned about a bore of the superconducting magnet for producing magnetic field gradients;
• a radio frequency (RF) system for transmitting RF excitation signals and receiving MR signals;
• a data acquisition system connected to the RF system to receive the MR signals from the RF system;
• a data processing system configured to:
• receive the MR signals from the data acquisition system;
• sort the MR signals into a plurality of MR data sets, each MR data set acquired at a distinct magnetic field strength;
• generate a plurality of image data sets corresponding to the plurality of MR data sets;
• and
• combine the plurality of image data sets to provide a corrected image having a reduced metal distortion;
• a pulse controller connected to the RF system, gradient system and data acquisition system that generates pulse sequences that include RF pulses from the RF system and gradient pulses from the gradient system;
• and
• a computer storage for storing the corrected image.