Gradient recalled echo-based $$$R_{2}^{*}$$$ measurements are sensitive to the degree of myelination of white matter fibres and their local orientation inside the magnetic field of the MR scanner. This orientation dependence has been observed experimentally and could be explained biophysically by anisotropic susceptibility of the myelin sheaths. In case of single, quantitative $$$R_{2}^{*}$$$ measurements the orientation dependence represents a potential confounder, since the observed $$$R_{2}^{*}$$$ would be biased by the sample’s orientation inside the scanner. Here, we propose an efficient method for separating $$$R_{2}^{*}$$$ into orientation dependent and independent components based on a biophysically motivated higher order $$$R_{2}^{*}$$$ decay model.
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