Magnetic susceptibility anisotropy: Cylindrical symmetry from macroscopically ordered anisotropic molecules and accuracy of MRI measurements using few orientations

► Macro magnetic susceptibility anisotropy (MSA) needs molecular anisotropy & order. ► MSA of cylindrically symmetric matter is estimated from n(≥3) orientations and DTI. ► Tissue symmetry & sampling orientations greatly affect noise in MSA estimate. ► MSA of major white matter tracts is mapped in vivo at 3T using 3 orientations.