An assessment of eddy current sensitivity and correction in single-shotdiffusion-weighted imaging

Abstract

Artefacts caused by eddy currents are a major problem in diffusion-weightedimaging. This is particularly acute in experiments in which a number of imageswith differing degrees of diffusion weighting and/or differently orienteddiffusion-weighting gradients need to be combined. The echo-planar imagingsequence is particularly sensitive to the effects of residual eddy currents,especially due to the low bandwidth in the phase-encoding direction.Two published schemes are investigated regarding the effectiveness of eddycurrent correction. That of Jezzard et al (1998 Magn. Reson. Med. 39 801-12) requires the acquisition of additional experimental data in orderto perform a post-acquisition correction, whereas that of Wider et al (1994J. Magn. Reson. A 108 255-8) attempts to reduce the eddy currentsdirectly. It is found that the latter experiment gives a somewhat superiorperformance and a combination of the two approaches results in an almostcomplete elimination of artefact.An alternative single-shot imaging experiment to echo-planar imaging is givenby sequences based on fast spin-echo methods, which should be insensitive tothe effects of constant eddy currents. It is shown that the intrinsiceddy-current-related artefact level in such experiments is indeed low,residual artefacts being attributed to eddy current decay during the echotrain. In situations of poor main magnetic field homogeneity or large eddycurrents such sequences may be gainfully used instead of echo-planar imaging.