Actively shielded transverse gradient coil for nuclear magnetic resonance tomography apparatus
First Claim
1. In a magnetic resonance imaging apparatus for producing a tomogram of an examination subject disposed in an examination volume of the apparatus, the improvement of an actively shielded transverse gradient coil arrangement comprising:
- a plurality of gradient coils;
each gradient coil being composed of a primary coil and a secondary coil disposed at a radial spacing from each other with the secondary coil lying on a larger radius than the primary coil;
means for supplying said primary coil and said secondary coil with current for causing said primary and secondary coil, in combination, to generate a linear magnetic field in a center of said examination volume; and
each of said primary coil and said secondary coil having windings which are farther from said center in an axial direction of the gradient coil and windings which are closer to said center, said windings of said primary coil and said secondary coil which are farther from said center having a smaller radial spacing from each other than said windings disposed closer to said center.
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Accused Products
Abstract
An actively shielded transverse gradient coil arrangement contains a primary coil and a secondary coil that are arranged at a radial spacing from one another. Turns of the primary coil and the secondary coil disposed farther from the center of the examination volume in an axial direction of the gradient coil arrangement have a smaller radial spacing from one another than do turns lying close to the center. The parasitic flux density can thus be minimized. This is particularly important in EPI sequences for avoiding physiological stimulations in the examination subject.
67 Citations
17 Claims
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1. In a magnetic resonance imaging apparatus for producing a tomogram of an examination subject disposed in an examination volume of the apparatus, the improvement of an actively shielded transverse gradient coil arrangement comprising:
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a plurality of gradient coils; each gradient coil being composed of a primary coil and a secondary coil disposed at a radial spacing from each other with the secondary coil lying on a larger radius than the primary coil; means for supplying said primary coil and said secondary coil with current for causing said primary and secondary coil, in combination, to generate a linear magnetic field in a center of said examination volume; and each of said primary coil and said secondary coil having windings which are farther from said center in an axial direction of the gradient coil and windings which are closer to said center, said windings of said primary coil and said secondary coil which are farther from said center having a smaller radial spacing from each other than said windings disposed closer to said center. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for constructing a transversal gradient coil formed by a conductor for producing a target field distribution with a prescribed current in a magnetic resonance imaging system, said method comprising the steps of:
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composing a gradient coil of a conductor having a plurality of windings forming a primary coil and a secondary coil disposed on respective winding surfaces with an azimuthal edge therebetween; giving said secondary coil a larger radius than said primary coil; disposing windings of said primary coil and said secondary coil which are farther from a center of an examination volume in an axial direction of the gradient coil at a smaller radial spacing from each other than windings of said primary coil and said secondary coil disposed closer to said center; subdividing said surfaces on which said windings of said primary coil and said secondary coil are disposed into a grid mesh network having grid openings and mesh branches; occupying each grid opening in said network with a modeled elementary coil in the form of a closed turn, each elementary coil generating a respective magnetic field; calculating the magnetic field generated by each of said elementary coils; defining a number of ampere-turns for each elementary coil using a fit algorithm based on said target field distribution; calculating a number of ampere-turns for each mesh branch by superimposing the ampere-turns for all of the elementary coils adjacent each mesh branch and thereby obtaining an ampere-turn density distribution over said network; successively integrating said ampere-turn density distribution over whole-numbers of turns along an integration path based on said prescribed current to obtain a plurality of points on said surfaces; and positioning said conductor on a carrier conforming to said surfaces in a configuration conforming to said points. - View Dependent Claims (16, 17)
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Specification