Design of Axial Shim Coils for Magnetic Resonance Imaging

An efficient design method of axial shim coils for Magnetic Resonance Imaging is presented. The axial shim coils are designed to improve magnetic field homogeneity which compensates for the unavoidable construction tolerances, cold shrink of magnet frame and some other negative effects. For simplifying design complexity of axial shim coils and reducing the difficulty of engineering, two sets of three pairs of single-layer coils in series are designed to eliminate all of the lower six orders of spherical harmonics (Z1, Z2, Z3, Z4, Z5, and Z6) for one time. Computing search method is employed to optimize positions of the shim coils. Details of the design method for a sample of a Baby MRI scanner and the calculation results are presented.