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From diffusion-weighted MRI to anomalous diffusion imaging

Hall, MG; Barrick, TR; (2008) From diffusion-weighted MRI to anomalous diffusion imaging. MAGN RESON MED , 59 (3) 447 - 455. 10.1002/mrm.21453.

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Abstract

We present a novel interpretation of non-monoexponential diffusion-weighted signal decay with b-value in terms of the theory of anomalous diffusion. Anomalous diffusion is the theory of diffusing particles in environments that are not locally homogeneous, such as brain tissue. In such environments the model of restricted diffusion commonly employed in the analysis of diffusion MR data is not valid, leading to a nonlinear time dependence for the mean-squared displacement of spins, and to a prediction of a stretched exponential form for the signal decay. We show that this prediction leads directly to a new parameter, the anomalous exponent, which may be measured from scan data and from this we can estimate a fractal dimension, d(w), which categorizes the complexity of the excursions of diffusing spins. We construct images of the anomalous exponent and fractal dimension from in vivo human brain data. Distributions of exponents and dimensions are constructed in grey and white matter and cerebrospinal fluid. We observe that these distributions peak at biologically plausible values consistent with previous studies: grey matter d(w) = 2.366 +/- 0.31, white matter d(w) = 2.587 +/- 0.39, CSF d(w) = 1.970 (mode). Marked contrast is observed between grey and white matter when compared with lateral ventricle CSF. We then consider the anisotropy of the value of the anomalous exponent and define quantities analogous to the mean diffusivity and fractional anisotropy that are commonly generated from diffusion tensor images.

Type: Article
Title: From diffusion-weighted MRI to anomalous diffusion imaging
DOI: 10.1002/mrm.21453
Keywords: brain, neurological, normal, anatomy, WATER DIFFUSION, APPARENT DIFFUSION, HUMAN BRAIN, ANALYTICAL-MODEL, SELF-DIFFUSION, WHITE-MATTER, ANISOTROPY, SYSTEMS, HETEROGENEITY, TISSUE
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health > ICH Developmental Neurosciences Prog
URI: http://discovery.ucl.ac.uk/id/eprint/83296
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