Towards Understanding the Anisotropy of Magnetization Transfer Parameters in Human White Matter
Andr Pampel 1 , Henrik Marschner 1 , Dirk K. Mller 1 , and Harald E. Mller 1
Max Planck Institute for Human Cognitive and
Brain Sciences, Leipzig, Germany
We examine the apparent dependence of qMT parameters, in
particular those of the T2 relaxation time of bound
protons, on the white matter fiber orientation. It is
found that those dependency results from parameter
fitting using the Super-Lorentzian lineshape, which
renders orientational dependency on other qMT
parameters. A novel RF absorption lineshape of the bound
pool considering the liquid-crystalline character of the
myelin sheath is derived that explains this dependence.
Data simulated using this lineshape were analyzed by
parameter fitting. A remarkable agreement was found in
the obtained parameters compared to those found in WM
regions with fractional anisotropy FA>0.7.
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