Can we re-design the gradient coil to make the eddy current field match the primary gradient field?

Introduction: Rapidly switched magnetic field gradients induce eddy currents in the nearby conducting structures of the MRI scanner. These eddy currents in turn generate an opposing and distorting transient magnetic field in the region of interest (ROI) with consequential image distortion. A tailored current pulse is usually applied to minimize the undesired effects of the eddy currents in the ROI. In order to successfully apply this current compensation technique, the primary and the secondary magnetic field produced by the eddy currents should have a similar spatial form in the ROI (field matching). Some efforts have been made to improve the linearity of the secondary and hence maximize the field matching figure [1,2]. In this work we present two approaches for gradient coil design that produces gradient fields with characteristics similar to those produced by the eddy currents. The first approach iteratively refines the gradient coil so that its primary field is similar to the induced secondary field. The second approach, termed as the mode coil [3], classifies as an eigenvector assignment [4] technique. The mode coil [3] produces maximal field matching with a large field non-linearity. This limitation is improved by designing an actively shielded mode gradient coil. The presented examples are used to demonstrate the advantages and disadvantages of the proposed techniques. Method: It is assumed that a 15 mm thick aluminum cylinder (surface C) of radius 377.5 mm and half length of 550 mm surrounds a cylindrical coil surface S of radius 320 mm and half length of 500 mm. When a low-frequency driving current is applied to the gradient set, the skin depth is very small under the aforementioned assumption, and