Patent ID: 6377148
Filing Date: 2002-04-23
Classification: G01R

Abstract:
A zonal shim coil having (i) a longitudinal axis and (ii) a predetermined shimming volume, and comprising a plurality of current-carrying windings which surround and are spaced along the longitudinal axis, said coil producing a magnetic field, the longitudinal component of which is given by: Bz&af;(r,Î¸)=&Sum;n=0âˆž&it;rn&af;(an0&it;Pn0&af;(cos&it;â€ƒ&it;Î¸))where an0 are the amplitudes of the zonal harmonics, Pn0(cos &thgr;) are Legendre polynomials, n is the order of the polynomial, and r and &thgr; are radial and azimuthal coordinates, respectively;wherein:(i) the coil generates a predetermined zonal harmonic whose order (nâ€²) is greater than or equal to 2; (ii) the coil has first and second ends which define a length 2L; and (iii) the predetermined shimming volume extends along the longitudinal axis from z=pL to z=qL, where (a) âˆ’1(b) |p|â‰ |q|; and (c) z=0 is midway between the first and second ends of the zonal shim coil.