Method to reduce eddy current effects in diffusion-weighted echo planar

Abstract

An eddy current correction method is provided for use in an MR system disposed to generate difflusion-weighted echo planar images by employing a bipolar diffusion-weighting gradient as well as the nominal components in an echo planar imaging pulse sequence. The correction method comprises the steps of deriving eddy current parameters (i.e., amplitude and time constant) associated with each eddy-current-induced magnetic field component caused by the diffusion-weighting gradient, and generating a set of correction terms, each of the correction terms being a function of the parameters. The method includes the further steps of modifyg a set of ideal echo planar imaging gradients and the receiver phase and frequency to respectively offset the eddy current induced magnetic field gradient and the spatially independent B.sub.0 -magnetic field. The modification occurs in two stages. Prior to data acquisition, errors are exactly corrected by altering the pre-phasing and the slice-refocusing gradient areas as well as the initial receiver phase. During data acquisition, the eddy current induced errors are approximately compensated for by adding offset gradients and dynamically changing the receiver phase and frequency using either a piece-wise-constant approximation or a constant approximation. Using either method, artifacts in diffusion-weighted echo planar images can be significantly reduced.