Anisotropy measure from three diffusion-encoding gradient directions

• Published in: Magnetic resonance imaging 2022-05, Vol.88, p.38-43
• Main Authors: Aja-Fernández, Santiago, París, Guillem, Martín-Martín, Carmen, Jones, Derek K., Tristán-Vega, Antonio
• Format: Article
• Language: English
• Subjects: Diffusion anisotropy; Diffusion MRI; Fast acquisition; Fractional anisotropy; White matter
• ISSN: 0730-725X; 1873-5894
• DOI: 10.1016/j.mri.2022.01.014

We propose a method that can provide information about the anisotropy and orientation of diffusion in the brain from only 3 orthogonal gradient directions without imposing additional assumptions. The method is based on the Diffusion Anisotropy (DiA) that measures the distance from a diffusion signal to its isotropic equivalent. The original formulation based on a Spherical Harmonics basis allows to go down to only 3 orthogonal directions in order to estimate the measure. In addition, an alternative simplification and a color-coding representation are also proposed. Acquisitions from a publicly available database are used to test the viability of the proposal. The DiA succeeded in providing anisotropy information from the white matter using only 3 diffusion-encoding directions. The price to pay for such reduced acquisition is an increment in the variability of the data and a subestimation of the metric on those tracts not aligned with the acquired directions. Nevertheless, the calculation of anisotropy information from DMRI is feasible using fewer than 6 gradient directions by using DiA. The method is totally compatible with existing acquisition protocols, and it may provide complementary information about orientation in fast diffusion acquisitions. [Display omitted]