A novel gradient design: simultaneous generation of fast switchable linear and high order field gradient for MR imaging

INTRODUCTION Shimming a magnetic field usually requires an additional set of complex coils which act independently from the linear gradient system used for MRI. Therefor a unique coil has to be developed for each field order, which is very extensive. In this study a novel matrix gradient design is presented, which is capable of generating both linear gradient fields for imaging and at the same time high order shim fields. The simultaneous generation of several orders can be achieved by using a set of individually driven coils. The complete gradient field results from the superposition of all these individual magnetic fields. This provides the possibility of creating a large variety of field profiles by driving each coil with a different current. This matrix gradient can not only provide strong linear gradients used for imaging but at the same time allows generating shim fields in order to compensate inhomogeneities in the main field. Driving the coils separately grants the advantage of switching shim and gradient fields very fast due to low inductivity of each single coil. With this new design it is possible to provide fast switchable imaging and shim gradients.