Correction of Eddy Current Distortions in High b-value and High Angular Resolution Diffusion Imaging

Introduction Diffusion tensor imaging (DTI) technology has a significant limitation in resolving intravoxel orientational heterogeneity within white matter of brain. Such limitations have prompted the development of high angular resolution diffusion imaging (HARDI) methods capable of resolving intravoxel fiber crossings, such as Diffusion Spectrum Imaging (DSI) and Q-Ball Imaging (QBI) [1]. However, because most of the HARDI techniques require high to ultra-high diffusion sensitizing gradients (b>4000 s/mm2), the capability of HARDI to provide valid and reliable information about tissue structures can be affected adversely by eddy current artifacts. One widely used post-processing algorithm, Iterative Cross-Correlation (ICC) [2], estimates distortions in DW images by cross-correlating them with an undistorted baseline image in terms of scaling, shear, and translation along the phaseencoding direction. One serious limitation of the original ICC algorithm, however, is its inability to correct image distortions at high b-values. The contrasts of cerebrospinal fluid (CSF), gray matter, and white matter in images acquired with high diffusion weighting differ greatly at different diffusion weightings or different diffusion gradient directions. Here we describe a new algorithm to detect eddy current distortions by modeling the distortion with the known x, y, and z components of diffusion gradients exclusively from DW images with close diffusion gradient directions.