Fibres at the Magic Angle Generated by Inappropriate Calibration (MAGIC)

Greg Daniel Parker^1,2, Derek K. Jones¹

Constrained spherical-harmonic deconvolution (CSD) provides resolution of intra-voxel crossing fibre orientation through deconvolution of an idealised (calibration) response from spherical harmonics fit to the target diffusion-weighted signal. Given a single-fibre low anisotropy target,we observe that, with high calibration anisotropies, spurious peaks are observed in the resultant deconvolution at elevations (relative to fibre orientation) consistent with the zero crossing (magic angle) and minima of the 2nd order Legendre polynomial, adversely affecting tractography. Bootstrap analysis however indicates that azimuthal distribution of such peaks appears uniform, allowing true crossing fibre to be distinguished through measurement of uncertainty.