Distance-based tractography in high angular resolution diffusion MRI

Abstract

High angular resolution diffusion imaging (HARDI) is a magnetic resonance imaging (MRI) technique, determining the diffusion of water molecules in tissue in vivo. HARDI is advantageous over the well-known diffusion tensor imaging (DTI), since it is able to extract more than one fiber orientation within a voxel and can therefore resolve crossing, kissing or fanning fiber tracts. However, multiple orientations per voxel require more sophisticated tractography approaches. In this paper we introduce a new deterministic fiber tracking method using the complete orientation distribution function (ODF) reconstructed from Q-ball imaging to enable tractography in challenging regions. Anisotropy classifiers are used to differentiate intra-voxel fiber populations and adjust a curvature threshold for one and multiple fiber configurations, respectively. In addition, we determine the most appropriate propagation direction in complex white matter regions, using the course of the current tract. To ensure tractography running within fiber bundles, a distance-based approach is integrated, which aims to maintain the initial distance of the seed point to the white matter boundary through the whole tracking. We evaluated our method using a phantom dataset featuring crossing, kissing and fanning fiber configurations and a human brain dataset, reconstructing the fanning of the corpus callosum and considering the region of the centrum semiovale.