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Author Notes:

Correspondence: Prof. Xiaoping P. Hu, Woodruff Memorial Building, 101 Woodruff Circle, Suite 2001, Emory University, Atlanta, Georgia 30322; Tel: (404)-712-2615; Fax: (404)-712-2707; Email: Xhu3@emory.edu

Acknowledgments: The authors would like to thank Drs. James Rilling, Longchuan Li, and Bhargav Kumar for helpful discussion.

Subject:

Research Funding:

Data collection was supported by grants from the NIH (PO1AG026423 and RO1EB002009).

Keywords:

  • Diffusion tensor imaging
  • Artifacts in MRI
  • Gradient cross-terms
  • Post-processing correction

Manifestation and Post-hoc Correction of Gradient Cross-term Artifacts in DTI

Tools:

Journal Title:

Magnetic Resonance Imaging

Volume:

Volume 30, Number 6

Publisher:

, Pages 764-773

Type of Work:

Article | Post-print: After Peer Review

Abstract:

Cross-terms between imaging and diffusion gradients, unaccounted for during tensor calculations, can lead to erroneous estimation of diffusivity and fractional anisotropy (FA) in regions of isotropic and anisotropic diffusion. Cross-term of magnitude 136.8 ± 1.6 s/mm2, artificially introduced in the slice-encode direction caused an increase in fractional anisotropy (FA) in isotropic phantom from 0.0546 ± 0.0001 to 0.0996 ± 0.0001, while the change in chimpanzee brain depended on the orientation of the white matter (WM). Mean diffusivity (MD), remained unchanged in isotropic phantom, but increased by ~20% in the WM due to cross-terms. A bias was observed in the principal eigenvectors in both phantom and chimpanzee brain, resulting in significant increase in midline crossing fibers along the bias than perpendicular to it in tractography in chimpanzee brain. Post-hoc correction of these artifacts was achieved by estimating the cross-term factors using calibration scans on an isotropic phantom and modifying the b-matrix before tensor calculation. Upon correction, the FA and MD values closely resembled the values obtained from sequence without cross-terms, and the bias in principal eigenvectors was eliminated. Customized sequences involving large b-values, high-resolution imaging, or long diffusion or echo times should therefore be evaluated and any residual cross-terms corrected before implementation.

Copyright information:

© 2012 Elsevier Inc. All rights reserved.

This is an Open Access work distributed under the terms of the Creative Commons Attribution-NonCommerical-NoDerivs 3.0 Unported License (http://creativecommons.org/licenses/by-nc-nd/3.0/).

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