Dynamic B0 shimming for improved fat saturation in magnetic resonance imaging (MRI)

A magnetic resonance imaging (MRI) system, comprising:

• a main magnet providing a magnetic field B0;
• a shim coil assembly;
• a gradient coil assembly;
• a radio-frequency (RF) coil;
• a controller in communication with the shim coil assembly, the gradient coil assembly, and the RF coil, the controller configured to perform operations of:
• driving the shim coil assembly with one set of shim coils of the MRI system with a first set of shimming currents to sufficiently alter a B0 field inhomogeneity of the magnetic field B0 within a region that includes a first imaging volume of interest such that the B0 field inhomogeneity with respect to a first species of protons within the region is substantially minimized;
• applying a preparation pulse by the RF coil assembly to the region such that magnetic resonance (MR) signals corresponding to a second species of protons in the region are substantially suppressed;
• in response to selecting the first imaging volume, driving the shim coil assembly with one set of shim coils of the MRI system with a second set of shimming currents to sufficiently alter the B0 field inhomogeneity of the magnetic field B0 within the first imaging volume of interest such that the B0 field inhomogeneity with respect to the first species of protons within the first imaging volume of interest is substantially reduced from before applying the second set of shimming currents;
• and
• obtaining, using an imaging pulse sequence, the magnetic resonance (MR) signals encoding the first species of protons from the first imaging volume of interest;
• generating the MR signals of the first imaging volume of interest, using the processor;
• and
• storing the MR signals to the database.

A method to compute sets of shimming currents for a magnetic resonance imaging (MRI) system having a main magnet that provides a magnetic field B0, a processor, a power amplifier, a shim coil assembly, a RF coil assembly, a database and a graphical user interface (GUI), the method comprising:

• obtaining a field map of a portion of the magnetic field B0;
• based on the field map, computing values of a first set of shimming currents, using the shim coil assembly having one set of shim coils, that substantially minimize saturation of a first species of protons within a region that covers a portion of a subject placed in the main magnet;
• obtaining location information of a first imaging volume of interest, the first imaging volume of interest included by the region;
• and
• based on the field map, and the location information of the first imaging volume of interest, computing values of a second set of shimming currents, using the shim coil assembly having one set of shim coils, that substantially minimize magnetic field inhomogeneity within the first imaging volume of interest with respect to the first species of protons;
• generating the MR signals of the first imaging volume of interest, using the processor;
• and
• storing the MR signals to the database.