Gradient field coil system for nuclear spin tomography

Claim 1

A gradient coil system for an image-generating, nuclear magnetic resonance tomographic apparatus, the gradient coil system being arranged on at least one hollow cylindrical carrier, the cylindrical carrier having a radius r and a central axis which extends along the z-direction of an orthogonal x, y, z coordinate system, the coordinate system having an origin located in the center of an imaging region within said carrier, the system having a base field magnet for producing a magnetic field B z in the z-direction, the magnetic field of said gradient coil system having a field gradient G z =δB z /δz which is essentially constant in the imaging region, the system further having at least two ring-shaped coils arranged symmetrically with respect to an x-y plane of symmetry through the center of the imaging region for conducting current in opposite directions, at least two pairs of saddle-shaped coils arranged approximately symmetrically with respect to the plane of symmetry for generating a field gradient G x =δB z /δx in the x-direction and a corresponding field gradient G y =δB z /δy in the y-direction, the field gradients being substantially constant, the saddle-shaped coils being coupled to a source of electrical current and each having respective straight conductor sections in the z-direction and first and second arc-shaped conductor sections in the circumferential direction perpendicular to the z-axis, said first arc-shaped conductor section being arranged adjacent said plane of symmetry and said second arc-shaped conductor section being arranged farther away from said plane of symmetry than said first arc-shaped conductor section, adjacent straight conductor sections in each pair of the saddle-shaped coils conducting electrical current in the same direction with respect to each other, and in the opposite direction with respect to corresponding straight conductor sections in the other pair of saddle-shaped coils arranged symmetrically on the other side of the plane of symmetry, the gradient coil system further comprising a third arc-shaped conductor section in each saddle-shaped coil, said third arc-shaped conductor section being connected in parallel with the first arc-shaped conductor section of the associated saddle-shaped coil, said third arc-shaped conductor section being arranged between the first and second arc-shaped conductor sections, the first, second and said third arc-shaped conductor sections being arranged at respective first, second, and third predetermined distances from the plane of symmetry and each containing a respective number of turns of conductive material, the first, second and said third arc-shaped conductor sections having respective predetermined electric linkage factors, magnitudes of said electric linkage factors being equal to a product of the electrical current being conducted through the respective arc-shaped conductor section and the number of turns of conductive material in the respective arc-shaped conductor section, the magnitudes of said electric linkage factors corresponding to said respective distances of the first, second, and said third arc-shaped conductor sections from the plane of symmetry.