Real-time shimming of polarizing field in magnetic resonance system
AssigneeMayo Foundation for Medical Education and Research
InventorsClifford R. Jack, Jr., Heidi A. Ward, Stephen J. Riederer
Life of this patent
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Abstract
An fMRI scan is performed with an MRI system in which a series of single shot EPI pulse sequences are performed to acquire a series of images. A shim navigator pulse sequence is interleaved with the EPI pulse sequence to acquire data with which the MRI system polarizing magnetic field can be measured. Measured changes in the polarizing field during the scan are employed to calculate corrective changes in the scan parameters that offset phase errors caused by changes in the polarizing field.
Claims18
A method for performing a magnetic resonance imaging scan of a subject with a magnetic resonance imaging (MRI) system, the steps comprise:
- a) performing a baseline shim navigator pulse sequence with the MRI system to acquire baseline shim navigator data indicative of the polarizing magnetic field magnitude along a selected direction across the subject;
- b) performing a series of imaging pulse sequences with the MRI system to acquire image data from which one or more images of the subject may be reconstructed;
- c) performing a series of shim navigator pulse sequences with the MRI system which are interleaved with the series of imaging pulse sequences to acquire shim navigator data indicative of the polarizing magnetic field magnitude along the selected direction across the subject prior to the performance of each imaging pulse sequence;
- d) calculating the change in polarizing magnetic field magnitude prior to performing each imaging pulse sequence using shim navigator data and baseline shim navigator data;
- and
- e) changing a scan parameter in the imaging pulse sequence based on the calculated change in polarizing magnetic field magnitude.
A method for performing a magnetic resonance imaging scan of a subject with a magnetic resonance imaging (MRI) system, the steps comprising:
- a) performing a series of imaging pulse sequences with the MRI system to acquire image data from an imaging volume and from which one or more images of the subject may be reconstructed;
- b) performing a series of shim navigator pulse sequences with the MRI system which are interleaved with the series of imaging pulse sequences to acquire shim navigator data indicative of a polarizing magnetic field magnitude;
- c) calculating changes in the polarizing magnetic field within the imaging volume using acquired shim navigator data;
- and
- d) prospectively changing the imaging pulse sequence during the performance of step a) to compensate for changes in the polarizing magnetic field that occur in the imaging volume;
- where performance of the shim navigator pulse sequence includes:
- i) producing an RF excitation pulse that produces transverse magnetization throughout the imaging volume;
- ii) producing a readout magnetic field gradient along one direction, which alternates in polarity to produce two shim navigator echo signals that are separated in time;
- and
- iii) acquiring the two shim navigator echo signals.
Dependencies are inferred from the claim text.