MRI self-shielded gradient coils

A self-shielded gradient coil for a magnetic resonance system comprising:

• an inner, tubular former which defines an examination region therein;
• an x-gradient coil and a y-gradient coil integrally bonded to the inner former;
• a z-gradient coil extending around and spaced from the inner former and the x and y-gradient coils such that a generally annular cooling passage is defined therebetween;
• an outer tubular former disposed around the z-gradient coil;
• and,
• x, y, and z shielding coils affixed to the outer former.

A method of designing a self-shielded gradient coil, the method comprising:

• selecting a radius for a primary gradient coil and a radius for a secondary, shielding gradient coil;
• designing a primary gradient coil pattern which achieves a preselected flux density and designing a corresponding secondary gradient coil;
• comparing a turns ratio of the primary and secondary gradient coils;
• iteratively (i) adjusting a length of the primary gradient coil, (ii) redesigning for the primary gradient coil to achieve the preselected flux density, (iii) redesigning the corresponding secondary gradient coil, and (iv) determining the turns ratio until an integer turns ratio is achieved;
• truncating the secondary gradients coil to a length about 20% longer than the length of the primary gradient coil.

A method of designing a self-shielding gradient coil for a magnetic resonance imaging apparatus, the method comprising:

• selecting an inner diameter, thickness, and maximum length of the self-shielding gradient coil;
• selecting a mean conductor radius for an x primary coil and a y primary coil;
• designating an outer diameter of the x and y primary coils and an associating supporting structure;
• selecting a mean z gradient coil radius which is at least 10 mm larger than said outer diameter;
• setting a maximum outer diameter, thickness, and length of a secondary coil assembly;
• establishing mean conductor radii of x, y, and z secondary coils;
• determining an energy minimized current distribution of x and y coil patterns and adjusting the length of the primary coil assembly to optimize shielding while constraining derivatives of the magnetic field in order to control linearity;
• iteratively adjusting x and y coil patterns and adjusting the primary coil length until a minimum energy storage and maximum shielding and linearity are attained;
• adjusting the primary z gradient coil radius to optimize shielding while constraining derivatives of the magnetic field to control linearity.

A method of designing self-shielded gradient coils for magnetic resonance imaging apparatus, the method comprising:

• selecting a diameter and length of a primary x, y-gradient coil in accordance with a selected diameter of an examination region therein;
• selecting a diameter of a secondary, shielding x, y-gradient coil in accordance with an inner diameter of a bore of the magnetic resonance apparatus;
• iteratively adjusting a length of the primary coil and recalculating discrete winding patterns which achieve a preselected current density in the primary gradient coil until the primary and secondary gradient coils have an integer turns ratio;
• selecting a diameter and length of a primary z-gradient coil, the primary z-gradient coil having a radius at least 10 mm larger than the primary x, y-gradient coil to provide a cooling air gap therebetween;
• selecting a radius and length of a secondary, shielding z-gradient coil, the length and diameter of the secondary z-gradient coil corresponding generally to the radius and length of the secondary x, y-gradient coil;
• iteratively adjusting the radius of the primary z-gradient coil and determining discrete z-gradient primary and secondary coil winding patterns until an integer turns ratio between the primary and secondary z-gradient coil winding patterns is achieved.