Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
. 2005 Jun;53(6):1423-31.
doi: 10.1002/mrm.20503.

Cross-subject comparison of principal diffusion direction maps

Armin Schwartzman  1 , Robert F Dougherty, Jonathan E Taylor
Affiliations
Comparative Study

Cross-subject comparison of principal diffusion direction maps

Armin Schwartzman et al. Magn Reson Med. 2005 Jun.

Abstract

Diffusion tensor imaging (DTI) data differ fundamentally from most brain imaging data in that values at each voxel are not scalars but 3 x 3 positive definite matrices also called diffusion tensors. Frequently, investigators simplify the data analysis by reducing the tensor to a scalar, such as fractional anisotropy (FA). New statistical methods are needed for analyzing vector and tensor valued imaging data. A statistical model is proposed for the principal eigenvector of the diffusion tensor based on the bipolar Watson distribution. Methods are presented for computing mean direction and dispersion of a sample of directions and for testing whether two samples of directions (e.g., same voxel across two groups of subjects) have the same mean. False discovery rate theory is used to identify voxels for which the two-sample test is significant. These methods are illustrated in a DTI data set collected to study reading ability. It is shown that comparison of directions reveals differences in gross anatomic structure that are invisible to FA.

PubMed Disclaimer

Figures

FIG. 1
FIG. 1
The bipolar Watson density on the sphere for κ = 1 (a) and κ = 5 (b).
FIG. 2
FIG. 2
(a) Histogram of the F statistic against the null density. (b) Q–Q plot of the F statistic against null quantiles. (c) Estimates of FDR as a function of threshold.
FIG. 3
FIG. 3
Significant voxels at slices z = 23 mm (a), 25 mm (b), and 27 mm (c).
FIG. 4
FIG. 4
The F statistic (a) and angle dispersion (degrees) of the principal direction (b) at slice z = 23 mm.
FIG. 5
FIG. 5
Mean direction for control group (a) and dyslexic group (b) at slice z = 23 mm.
FIG. 6
FIG. 6
Mean FA for control group (a) and dyslexic group (b) at slice z = 23 mm.
FIG. 7
FIG. 7
The t test statistic (a) and pooled SD of FA (b) at slice z = 23 mm.
See this image and copyright information in PMC

References

    1. Basser PJ. Inferring microstructural features and the physiological state of tissues from diffusion-weighted images. NMR Biomed. 1995;8:333–344. - PubMed
    1. Basser PJ, Pierpaoli C. Microstructural and physiological features of tissues elucidated by quantitative-diffusion-tensor MRI. J Magn Reson B. 1996;111:209–219. - PubMed
    1. LeBihan D, Mangin JF, Poupon C, Clark CA, Pappata S, Molko N, Chabriat H. Diffusion tensor imaging: concepts and applications. J Magn Reson Imaging. 2001;13:534–546. - PubMed
    1. Bammer R, Auer M, Keeling SL, Agustin M, Stables LA, Prokesch RW, Stollberger R, Moseley ME, Fazekas F. Diffusion tensor imaging using single-shot SENSE-EPI. Magn Reson Med. 2002;48:128–136. - PubMed
    1. Mori S, Kaufmann WE, Davatzikos C, Stieltjes B, Amodei L, Fredericksen K, Pearlson GD, Melhem ER, Solaiyappan M, Raymond GV, Moser HW, Van Zijl PC. Imaging cortical association tracts in the human brain using diffusion-tensor-based axonal tracking. Magn Reson Med. 2002;47:215–223. - PubMed

Publication types

LinkOut - more resources