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Effect of experimental parameters on high b ‐value q ‐space MR images of excised rat spinal cord
Author(s) -
NossinManor Revital,
Duvdevani Revital,
Cohen Yoram
Publication year - 2005
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.20519
Subject(s) - diffusion , nuclear magnetic resonance , chemistry , anisotropy , contrast (vision) , spinal cord , diffusion mri , perpendicular , white matter , displacement (psychology) , anisotropic diffusion , physics , optics , geometry , mathematics , magnetic resonance imaging , medicine , radiology , psychotherapist , thermodynamics , psychology , psychiatry
The influence of diffusion time (Δ), gradient duration (δ), and TE on the appearance of high b ‐value q ‐space diffusion MR images of excised rat spinal cord (SC) was evaluated. The water signal decays in the white (WM) and gray matter (GM) were analyzed when the diffusion was measured perpendicular (⟂) and parallel (‖) to the fibers of the SC, using three different approaches: single‐component q ‐space analysis, the biexponential model, and the bi‐Gaussian fit of the displacement distribution profile. Probability and displacement contrast and anisotropy indices were calculated for the WM and GM. It was found that WM/GM contrast increases as the diffusion time is increased when diffusion is measured perpendicular to the long axis of the SC. At a diffusion time of 50 ms, when diffusion was measured parallel to the fibers of the SC, the displacement was found to be higher for GM as compared to WM. For this direction the WM/GM contrast increased when diffusion time was increased, although here the changes were much less pronounced than for the perpendicular direction. The WM/GM displacement contrast nearly disappears for a diffusion time of 150 ms, when diffusion is measured parallel to the fibers of the SC. As expected, the anisotropy indices were found to be higher in WM than in GM, and increased with the increase in diffusion time. Both δ and TE affected the extracted parameters. It was found that long δ and long TE overemphasizes the apparent slow‐diffusing water component of the SC, which is also the more restricted one. It is demonstrated that the single‐component q ‐space analysis best describes diffusion in WM when diffusion is measured perpendicular to the fibers of the SC. In other cases, a more complete description is obtained by using two‐component models. Magn Reson Med 54:96–104, 2005. © 2005 Wiley‐Liss, Inc.