Active shimming for low-field magnetic resonance imaging

A method of active shimming for a magnet resonance imaging (MRI) system, the MRI system comprising a first gradient coil, a second gradient coil, a third gradient coil, and a permanent magnet, wherein the permanent magnet is configured to generate a magnetic field B0 having a low field strength, the method comprising:

• selecting a set of candidate shimming configurations, wherein the set of candidate shimming configurations comprises first current values associated with the first gradient coil from a first range of current values, second current values associated with the second gradient coil from a second range of current values, and third current values associated with the third gradient coil from a third range of current values, and wherein the set of candidate shimming configurations comprises candidate shimming configurations derived based on combining each of the first current values with each of the second current values and each of the third current values;
• applying, for each candidate shimming configuration, a pulse sequence;
• acquiring, for each pulse sequence, a magnetic resonance (MR) signal;
• determining, for each MR signal, a signal bandwidth based on a frequency domain of the MR signal;
• and
• designating a shimming configuration for the MRI system, wherein the shimming configuration is based on the candidate shimming configuration corresponding to the narrowest signal bandwidth of the MR signals for the set of candidate shimming configurations.

A method of active shimming for a magnet resonance imaging (MRI) system, the MRI system comprising a first gradient coil, a second gradient coil, a third gradient coil, and a permanent magnet, wherein the permanent magnet is configured to generate a magnetic field B0 having a low field strength, the method comprising:

• selecting a set of candidate shimming configurations, wherein the set of candidate shimming configurations comprises first current values associated with the first gradient coil from a first range of current values, second current values associated with the second gradient coil from a second range of current values, and third current values associated with the third gradient coil from a third range of current values;
• applying, for each candidate shimming configuration, at least two pulse sequences;
• acquiring, for each pulse sequence, at least two magnetic resonance (MR) signals for each candidate shimming configuration;
• determining, for each candidate shimming configuration, an average signal bandwidth based on the at least two MR signals acquired for the candidate shimming configuration;
• determining, for each MR signal, a signal bandwidth based on a frequency domain of the MR signal;
• and
• designating a shimming configuration for the MRI system, wherein the shimming configuration is based on the candidate shimming configuration corresponding to the narrowest signal bandwidth of the MR signals for the set of candidate shimming configurations.