Correcting eddy current and motion effects by affine whole‐brain registrations: Evaluation of three‐dimensional distortions and comparison with slicewise correction

Eddy‐current (EC) and motion effects in diffusion‐tensor imaging (DTI) bias the estimation of quantitative diffusion indices, such as the fractional anisotropy. Both effects can be retrospectively corrected by registering the strongly distorted diffusion‐weighted images to less‐distorted T2‐weighted images acquired without diffusion weighting. Two different affine spatial transformations are usually employed for this correction: slicewise and whole‐brain transformations. However, a relation between estimated transformation parameters and EC distortions has not been established yet for the latter approach. In this study, a novel diffusion‐gradient‐direction–independent estimation of the EC field is proposed based solely on affine whole‐brain registration parameters. Using this model, it is demonstrated that a more distinct evaluation of the whole‐brain EC effects is possible if the through‐plane distortion was considered in addition to the well‐known in‐plane distortions. Moreover, a comparison of different whole‐brain registrations relative to a slicewise approach is performed, in terms of the relative tensor error. Our findings suggest that for appropriate intersubject comparison of DTI data, a whole‐brain registration containing nine affine parameters provides comparable performance (between 0 and 3%) to slicewise methods and can be performed in a fraction of the time. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.