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Comment
. 2014 Jun;71(6):1956-8.
doi: 10.1002/mrm.25214. Epub 2014 Apr 3.

Biophysical mechanisms of myelin-induced water frequency shifts

Dmitriy A Yablonskiy  1 , Alexander L Sukstanskii
Affiliations
Comment

Biophysical mechanisms of myelin-induced water frequency shifts

Dmitriy A Yablonskiy et al. Magn Reson Med. 2014 Jun.
No abstract available

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Figures

FIG. 1.
FIG. 1.
Schematic structure of an axon with radius Raxon surrounded by a myelin sheath of the external radius Rext, consisting of lipid layers of thickness d (marked in gray) separated by aqueous phases (layers) of thickness dw. Each lipid layer is formed by highly organized, radially oriented long molecules (shown as an ellipsoids at left) with anisotropic magnetic susceptibility. In the presence of magnetic field B0, the lipid layers become magnetized and create an additional magnetic field that can be described as a result of magnetostatic charges ρ = −div M formed on the layers’ surfaces (surface charges) and inside the lipid layers (volume charges). The surface magnetostatic charges (which are of interest for the proposed “hop in, hop out” mechanism and are shown as + and − signs) are equal to ρS = ±H0 sin α ⋅ cosφ ⋅ χ∥, where α and φ are the polar and azimuthal angles (Z-direction is along the axon). The signs of the surface charges and the direction of the field H within the lipid layers correspond to χ∥ < 0. Blue dots represent water molecules performing a “Hokey Pokey”–like dance from aqueous to lipid layers. When a water molecule jumps from water layer to lipid layer, it experiences an additional field H (shown as arrows) induced by the surface charges. The projection of this field on B0 is equal to H = −H0 ⋅ χ∥ ⋅ sin2 α ⋅ cos2 φ.
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