Dynamic low-order shimming for arterial spin labeling

A method comprising:

• applying respective first shim currents to a plurality of first-order shim coils of an MR scanner;
• applying respective second shim currents to a plurality of second-order shim coils of the MR scanner;
• setting a center frequency of an RF system of the MR scanner to a first center frequency;
• executing a labeling phase of an arterial spin labeling pulse sequence while the respective first shim currents are applied to the plurality of first-order shim coils, the respective second shim currents are applied to the plurality of second-order shim coils, and the center frequency of the RF system is set to the first center frequency;
• during a post-labeling delay of the arterial spin labeling pulse sequence, switching the respective first shim currents applied to the plurality of first-order shim coils to respective third shim currents and switching the center frequency of the RF system to a second center frequency;
• executing a readout phase of the arterial spin labeling pulse sequence to acquire first MR data from an imaging volume of a subject while the respective third shim currents are applied to the plurality of first-order shim coils, the respective second shim currents are applied to the plurality of second-order shim coils, and the center frequency of the RF system is set to the second center frequency;
• and
• generating an image based on the first MR data.

A non-transitory computer-readable medium storing program code executable by at least one processing unit to cause a computing system to:

• instruct application of respective first shim currents to a plurality of first-order shim coils of an MR scanner;
• instruct application of respective second shim currents to a plurality of second-order shim coils of the MR scanner;
• instruct application setting of a center frequency of an RF system of the MR scanner to a first center frequency;
• instruct the MR scanner to execute a labeling phase of an arterial spin labeling pulse sequence while the respective first shim currents are applied to the plurality of first-order shim coils, the respective second shim currents are applied to the plurality of second-order shim coils, and the center frequency of the RF system is set to the first center frequency;
• during a post-labeling delay of the arterial spin labeling pulse sequence, instruct switching of the respective first shim currents applied to the plurality of first-order shim coils to respective third shim currents and switching of the center frequency of the RF system to a second center frequency;
• instruct the MR scanner to execute a readout phase of the arterial spin labeling pulse sequence to acquire first MR data from an imaging volume of a subject while the respective third shim currents are applied to the plurality of first-order shim coils, the respective second shim currents are applied to the plurality of second-order shim coils, and the center frequency of the RF system is set to the second center frequency;
• and
• generate an image based on the first MR data.