A Design Technique of MRI Active Shield Gradient Coil Using Node Current Potentials and Triangular Finite Elements

A design technique to calculate winding patterns of active shield gradient coils has been developed with the design tool using current potential and singular value decomposition (SVD) (DUCAS), which is a computer code to construct sheet current distributions on arbitrary surfaces using current potential (CP), triangular finite elements, and regularization of truncated SVD. The DUCAS calculates sheet currents on current carrying surfaces (CCSs) of CCS1 for the main coil and CCS2 for the shield coil, so as to reconstruct a gradient field and a magnetic field shielding iteratively. The iterative calculation converged in roughly ten steps. The obtained magnetic field showed very accurate shielding of below 10^-7 T with the gradient magnetic field. Then, the sheet currents on CCSs were discretized as filament currents for conductor placements along CP contours. The applicability of this technique has been confirmed by test designs. Furthermore, it was understood that optimization of the CCS2 shape could be possible using the developed technique.