Localized eddy current compensation using quantitative field mapping

Eddy current effects induced by switched gradients in proximal conducting structures are traditionally reduced by applying pre-emphasis currents whose amplitudes and decay characteristics must be set to offset the eddy current fields. We present an expeditious, localized, and quantitative method for mapping and adjusting the parameters for eddy current compensation. Mapping is based on analysis of projections as used in the fast automatic shimming technique by mapping along projections (FASTMAP). Adjustment methods are demonstrated in high-field horizontal bore systems. The proposed localized eddy current mapping technique may also be used for localized measurements in situations where asymmetric conducting structures may cause nonlinear eddy current fields, such as in interventional MRI and open magnet designs. (C) 1998 Academic Press.