Magnetic resonance apparatus and methods with shim adjustment
First Claim
Patent Images
1. A method of magnetic resonance imaging comprising the steps of:
- (a) positioning a subject adjacent a single-sided static field magnet;
(b) actuating said static field magnet to provide a plurality of different magnetic fields at different times within an imaging region of the subject, each such field defining a plurality of slices of constant field magnitude including a best slice most closely approximating a preselected shape intersecting an axis, the best slices of said different fields intercepting the axis at different locations;
(c) tuning RF transmission and reception apparatus to apply RF excitation to the subject so as to elicit and receive magnetic resonance signals selectively from one or more slices defined by each field in the vicinity of the best slice defined by such field; and
(d) applying magnetic field gradients in directions perpendicular to the axis so as to spatially encode the magnetic resonance signals from each slice.
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Abstract
A magnet for magnetic resonance imaging of the type arranged to provide fields suitable for imaging in an imaging region outside of the physical structure of the magnet, such as a magnet including plural concentric superconducting coils, generates a field having near-zero radial curvature at one location. Shim coils are actuated to adjust this location in synchronism with tuning of the RF transceiver for slice selection, so that when each slice is selected, that slice is coincident with the location of near-zero radial curvature.
63 Citations
17 Claims
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1. A method of magnetic resonance imaging comprising the steps of:
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(a) positioning a subject adjacent a single-sided static field magnet;
(b) actuating said static field magnet to provide a plurality of different magnetic fields at different times within an imaging region of the subject, each such field defining a plurality of slices of constant field magnitude including a best slice most closely approximating a preselected shape intersecting an axis, the best slices of said different fields intercepting the axis at different locations;
(c) tuning RF transmission and reception apparatus to apply RF excitation to the subject so as to elicit and receive magnetic resonance signals selectively from one or more slices defined by each field in the vicinity of the best slice defined by such field; and
(d) applying magnetic field gradients in directions perpendicular to the axis so as to spatially encode the magnetic resonance signals from each slice. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Magnetic resonance imaging apparatus comprising:
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(a) a single-sided main field magnet arranged to provide a main magnetic field defining a plurality of slices of constant field magnitude including a best slice most closely approximating a preselected shape intersecting at axis at a sweet spot outside of a main field magnet;
(b) one or more shim coils;
(c) a shim coil driver arranged to actuate said shim coils to provide one or more shim fields such that a resultant field produced by superposition of each shim field and the main field has a best slice which most closely approximates the preselected shape at a sweet spot or location along the axis different from the axial location of the sweet spot of the main field alone. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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Specification