Recovery of signal void arising from field inhomogeneities in echo planar imaging
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1. A method for producing an image of a subject with an MRI system, the steps comprising:
- performing a prescan to produce a rephasing map, the prescan including;
a) acquiring a plurality of pilot images of the subject using an NMR pulse sequence that employs an imaging magnetic field gradient, and wherein the imaging magnetic field gradient is set to different values in the plurality of pilot image acquisitions;
b) calculating the optimal imaging magnetic field gradient value for each pixel in the pilot images by examining magnitudes of the corresponding pixels in the plurality of acquired pilot images;
c) storing the optimal imaging magnetic field gradient values at corresponding pixel locations in the rephasing map;
d) determining an imaging magnetic field gradient setting using the values stored in the rephasing map; and
e) performing a scan of the patient using the NMR pulse sequence with the imaging magnetic field gradient setting.
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Abstract
A prescan process is performed in which an EPI pulse sequence acquires a series of pilot images. Each pilot image is acquired with a different slice selection refocusing gradient and a rephasing map is produced which indicates the optimal refocusing gradient to be used for each pixel. The rephasing map is used to determine the optimal refocusing gradient amplitudes to use in a subsequent scan to reduce signal drop out caused by susceptibility gradients.
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13 Claims
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1. A method for producing an image of a subject with an MRI system, the steps comprising:
performing a prescan to produce a rephasing map, the prescan including; a) acquiring a plurality of pilot images of the subject using an NMR pulse sequence that employs an imaging magnetic field gradient, and wherein the imaging magnetic field gradient is set to different values in the plurality of pilot image acquisitions; b) calculating the optimal imaging magnetic field gradient value for each pixel in the pilot images by examining magnitudes of the corresponding pixels in the plurality of acquired pilot images; c) storing the optimal imaging magnetic field gradient values at corresponding pixel locations in the rephasing map; d) determining an imaging magnetic field gradient setting using the values stored in the rephasing map; and e) performing a scan of the patient using the NMR pulse sequence with the imaging magnetic field gradient setting. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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