Patent ID: 7330031

Claim:
A matrix shim system having a plurality of annular coils whose axes coincide with a z-axis, the shim system generating magnetic field components superimposed on a main static magnetic field parallel to the z-axis, the magnetic field components-acting to homogenize a magnetic field component of the main static magnetic field along the z-axis in a volume of interest centered at an origin of the z-axis, the system comprising: g groups G 1 . . . G g of coils, with g being a natural number ≧1, wherein each group G i consists of at least two single annular coils C i1 . . . C ic(i) connected in series, with i: index number of the group, and c(i) being the amount of annular coils within group i, each group G i being designed to generate, in use, a magnetic field B z ⁡ ( G i ) = ∑ n = 0 ∞ ⁢ A n ⁢ ⁢ 0 ⁡ ( G i ) · T n ⁢ ⁢ 0 = ∑ n = 0 ∞ ⁢ [ A n ⁢ ⁢ 0 ⁡ ( G i ) · R n ] · [ T n ⁢ ⁢ 0 / R n ] , with A n0 : series coefficients of order n and degree 0, T n0 : spherical harmonic function of order n and degree 0; and n: index of summation, wherein a highest value B max of harmonic field components of an order between 2 and N of group G i is given by B max ( G i )=max{| A 20 ( G i )· R 2 |, . . . , |A N0 ( G i )· R N |}, and for each group G i , there are at least two values of n for which  A n ⁢ ⁢ 0 ⁡ ( G i ) · R n  B max ⁡ ( G i ) ≥ 0.5 ⁢ ⁢ and ⁢ ⁢ ⁢ N ≥ n ≥ 2 , with N: a total number of current supplies connected to annular coils of the matrix shim system, and R: a smallest inside radius of any of the annular coils of the matrix shim system; and an individual, adjustable electrical current supply for each group G i of coils.