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The effect of rotational angle and experimental parameters on the diffraction patterns and micro-structural information obtained from q-space diffusion NMR: implication for diffusion in white matter fibers

Avram, Liat, Assaf, Yaniv and Cohen, Yoram 2004. The effect of rotational angle and experimental parameters on the diffraction patterns and micro-structural information obtained from q-space diffusion NMR: implication for diffusion in white matter fibers. Journal of Magnetic Resonance 169 (1) , pp. 30-38. 10.1016/j.jmr.2004.03.020

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Abstract

Diffusion NMR may provide, under certain experimental conditions, micro-structural information about confined compartments totally non-invasively. The influence of the rotational angle, the pulse gradient length and the diffusion time on the diffusion diffraction patterns and q-space displacement distribution profiles was evaluated for ensembles of long cylinders having a diameter of 9 and 20 μm. It was found that the diffraction patterns are sensitive to the rotational angle (α) and are observed only when diffusion is measured nearly perpendicular to the long axis of the cylinders i.e., when α=90°±5° under our experimental conditions. More importantly, we also found that the structural information extracted from the displacement distribution profiles and from the diffraction patterns are very similar and in good agreement with the experimental values for cylinders of 20 μm or even 9 μm, when data is acquired with parameters that satisfy the short gradient pulse (SGP) approximation (i.e., δ→0) and the long diffusion time limit. Since these experimental conditions are hardly met in in vitro diffusion MRI of excised organs, and cannot be met in clinical MRI scanners, we evaluated the effect of the pulse gradient duration and the diffusion time on the structural information extracted from q-space diffusion MR experiments. Indeed it was found that, as expected, accurate structural information, and diffraction patterns are observed when Δ is large enough so that the spins reach the cylinders’ boundaries. In addition, it was found that large δ results in extraction of a compartment size, which is smaller than the real one. The relevance of these results to q-space MRI of neuronal tissues and fiber tracking is discussed.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Neuroscience and Mental Health Research Institute (NMHRI)
Publisher: Elsevier
ISSN: 1090-7807
Last Modified: 21 Aug 2019 02:20
URI: http://orca.cf.ac.uk/id/eprint/91875

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