White matter integrity measured by fractional anisotropy correlates poorly with actual individual fiber anisotropy

  • Authors:

  • Alex D. Leow;Liang Zhan;Siwei Zhu;Nathan Hageman;Ming-Chang Chiang;Marina Barysheva;Arthur W. Toga;Katie L. McMahon;Greig I. de Zubicaray;Margaret J. Wright;Paul M. Thompson

  • Affiliations:

  • Laboratory of Neuro Imaging, Department of Neurology, UCLA School of Medicine and Neuropsychiatric Institute, UCLA School of Medicine, Los Angeles, CA;Laboratory of Neuro Imaging, Department of Neurology, UCLA School of Medicine, Los Angeles, CA;Department of Mathematics, UCLA, Los Angeles, CA;Laboratory of Neuro Imaging, Department of Neurology, UCLA School of Medicine, Los Angeles, CA;Laboratory of Neuro Imaging, Department of Neurology, UCLA School of Medicine, Los Angeles, CA;Laboratory of Neuro Imaging, Department of Neurology, UCLA School of Medicine, Los Angeles, CA;Laboratory of Neuro Imaging, Department of Neurology, UCLA School of Medicine, Los Angeles, CA;University of Queensland, Functional MRI Laboratory, Centre for Magnetic Resonance, Brisbane, Australia;University of Queensland, Functional MRI Laboratory, Centre for Magnetic Resonance, Brisbane, Australia;Queensland Institute of Medical Research, Brisbane, Australia;Laboratory of Neuro Imaging, Department of Neurology, UCLA School of Medicine, Los Angeles, CA

  • Venue:
  • ISBI'09 Proceedings of the Sixth IEEE international conference on Symposium on Biomedical Imaging: From Nano to Macro
  • Year:
  • 2009

Quantified Score

Hi-index 0.01

Visualization

Abstract

Fractional anisotropy (FA), a very widely used measure of fiber integrity based on diffusion tensor imaging (DTI), is a problematic concept as it is influenced by several quantities including the number of dominant fiber directions within each voxel, each fiber's anisotropy, and partial volume effects from neighboring gray matter. High-angular resolution diffusion imaging (HARDI) can resolve more complex diffusion geometries than standard DTI, including fibers crossing or mixing. The tensor distribution function (TDF) can be used to reconstruct multiple underlying fibers per voxel, representing the diffusion profile as a probabilistic mixture of tensors. Here we found that DTI-derived mean diffusivity (MD) correlates well with actual individual fiber MD, but DTI-derived FA correlates poorly with actual individual fiber anisotropy, and may be suboptimal when used to detect disease processes that affect myelination. Analysis of the TDFs revealed that almost 40% of voxels in the white matter had more than one dominant fiber present. To more accurately assess fiber integrity in these cases, we here propose the differential diffusivity (DD), which measures the average anisotropy based on all dominant directions in each voxel.