Dynamic B

1. A method to perform fat saturation on a magnetic resonance imaging (MRI) system having a main magnet providing a magnetic field B 0 , the method comprising:

driving a shim coil assembly of the MRI system with a first set of shimming currents to sufficiently alter a B 0 field inhomogeneity of the magnetic field B 0 within a region that includes a first imaging volume of interest such that water saturation inside the region is reduced from before the first set of shimming currents are applied;

applying a fat saturation pulse to the region;

identifying the first imaging volume of interest from the region;

driving the shim coil assembly of the MRI system with a second set of shimming currents to alter the B 0 field inhomogeneity of the magnetic field B 0 within the first imaging volume of interest such that the B 0 field inhomogeneity within the first imaging volume of interest is reduced from before the second set of shimming currents were applied; and

obtaining magnetic resonance (MR) signals from the first imaging volume of interest using an imaging pulse sequence.

2. The method of claim 1 , wherein obtaining magnetic resonance signals from the first imaging volume of interest comprises:

applying gradient pulses to encode MR signals from the first imaging volume of interest; and

in response to the gradient pulses, acquiring the MR signals from the first imaging volume of interest.

3. The method of claim 1 , wherein the imaging pulse sequence comprises at least one of: a gradient-echo pulse sequence, a spin-echo pulse sequence, a steady-state free precession (SSFP) pulse sequence, and an echo-planar imaging (EPI) pulse sequence.

4. The method of claim 1 , wherein driving the shim coil assembly of the MRI system with a first set of shimming currents comprises: driving the shim coil assembly of the MRI system with a first set of shimming currents to substantially minimize water saturation within the region.

5. The method of claim 1 , further comprising:

identifying a second imaging volume of interest from the region;

subsequently driving the shim coil assembly of the MRI system with a third set of shimming currents to alter the B 0 field inhomogeneity of the magnetic field B 0 within the second imaging volume of interest such that the B 0 field inhomogeneity within the second imaging volume of interest is reduced from before the third set of shimming currents were applied; and

obtaining magnetic resonance signals from the second imaging volume of interest using the imaging pulse sequence.

6. The method of claim 1 , further comprising:

placing a subject in the main magnet such that the region covers a portion of the subject.

7. The method of claim 6 , wherein the portion of the subject includes at least one of:

an abdominal organ of the subject, a breast of the subject, a neck of the subject, an extremity of the subject, and a head of the subject.

8. The method of claim 1 , wherein prior to obtaining the MR signals from the first imaging volume of interest: applying a first slice-select gradient while applying a first radio-frequency (RF) pulse such that protons from the first imaging volume of interest are excited by the first RF pulse.

9. A magnetic resonance imaging (MRI) system, comprising:

a main magnet providing a magnetic field B 0 ;

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 of the MRI system with a first set of shimming currents to sufficiently alter a B 0 field inhomogeneity of the magnetic field B 0 within a region that includes a first imaging volume of interest such that water saturation inside the region is reduced from before the first set of shimming currents are applied;

applying a fat saturation pulse to the region;

identifying the first imaging volume of interest from the region;

driving the shim coil assembly of the MRI system with a second set of shimming currents to alter the B 0 field inhomogeneity of the magnetic field B 0 within the first imaging volume of interest such that the B 0 field inhomogeneity within the first imaging volume of interest is reduced from before the second set of shimming currents were applied; and

obtaining magnetic resonance (MR) signals from the first imaging volume of interest using an imaging pulse sequence.

10. The MRI system of claim 9 , wherein obtaining magnetic resonance signals from the first imaging volume of interest comprises:

applying gradient pulses to encode MR signals from the first imaging volume of interest; and

in response to the gradient pulses, acquiring the MR signals from the first imaging volume of interest.

11. The MRI system of claim 9 , wherein the imaging pulse sequence comprises at least one of: a gradient-echo pulse sequence, a spin-echo pulse sequence, a steady-state free precession (SSFP) pulse sequence, and an echo-planar imaging (EPI) pulse sequence.

12. The MRI system of claim 9 , wherein driving the shim coil assembly of the MRI system with a first set of shimming currents comprises: driving the shim coil assembly of the MRI system with a first set of shimming currents to substantially minimize water saturation within the region.

13. The MRI system of claim 9 , wherein the operations further comprise:

identifying a second imaging volume of interest from the region;

subsequently driving the shim coil assembly of the MRI system with a third set of shimming currents to alter the B 0 field inhomogeneity of the magnetic field B 0 within the second imaging volume of interest such that the B 0 field inhomogeneity within the second imaging volume of interest is reduced from before the third set of shimming currents were applied; and

obtaining magnetic resonance signals from the second imaging volume of interest using the imaging pulse sequence.

14. The MRI system of claim 9 , wherein the region covers a portion of a subject placed in the main magnet.

15. The MRI system of claim 14 , wherein the portion of the subject includes at least one of:

an abdominal organ of the subject, a breast of the subject, a neck of the subject, an extremity of the subject, and a head of the subject.

16. The MRI system of claim 9 , wherein prior to obtaining the MR signals from the first imaging volume of interest: applying a first slice-select gradient while applying a first radio-frequency (RF) pulse such that protons from the first imaging volume of interest are excited by the first RF pulse.

17. A method to compute sets of shimming currents for a magnetic resonance imaging (MRI) system having a main magnet that provides a magnetic field B 0 , the method comprising:

obtaining a field map of a portion of the magnetic field B 0 ;

based on the field map, computing values of a first set of shimming currents that substantially minimize water saturation 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 that substantially minimize magnetic field inhomogeneity within the first imaging volume of interest.

18. The method of claim 17 , further comprising:

obtaining a fat map of the portion of the subject placed in the main magnet; and

obtaining a water map of the portion of the subject placed in the main magnet.

19. The method of claim 18 , wherein the values of a first and second sets of shimming currents are computed based on the field map, the fat map, and the water map.

20. The method of claim 17 , wherein the first set of shimming currents substantially maximize fat saturation within the region that covers the portion of the subject.