FDTD Analysis of transient eddy currents induced by gradient coil switching in MRI
A. Trakic, H. Wang, F. Liu, H. S. Lopez, S. Crozier School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD, Australia Synopsis: Most Magnetic Resonance Imaging (MRI) spatial encoding techniques employ low-frequency pulsed magnetic field gradients that undesirably induce multi-exponentially decaying eddy currents in nearby conducting structures of the MRI scanner. This is particularly problematic in superconducting system components. The eddy currents degrade the switching performance of the gradient system, distort the MRI image and introduce thermal loads in the cryostat. A recently proposed three-dimensional (3D), low-frequency Finite-Difference Time-Domain (FDTD) method in cylindrical coordinates (Trakic et al., Cylindrical 3D FDTD algorithm for the computation of low frequency transient eddy currents in MRI, ISMRM 2006, submitted) is employed to analyse temporal eddy currents and manifest effects (e.g. B0-shift) induced by pulsed actively shielded symmetric/asymmetric transverse x-gradient head and whole body z-coils.