A time-harmonic target-field method for designing shielded RF coils in MRI

An inverse method for designing shielded, high-frequency RF coil systems is presented. A time-harmonic target-field approach is taken to find current densities on primary and shield RF coils. The correspondingly induced magnetic field is required to be homogeneous upon an asymmetrically located target region within the scanner and to be zero over an exterior target region. The finite length of the coil system is represented via a Fourier series expansion for the current density. Some new regularization penalty functions are considered in the solution process. A technique is given for creating coil winding patterns from complex, time-dependent current densities. To demonstrate the power of this design method, several coil windings are displayed for the primary and shield coils along with the corresponding fields.