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Abstract #4409

Resolving orientation-specific diffusivities and transverse relaxation rates in heterogenous brain tissue

Alexis Reymbaut1,2, João Pedro de Almeida Martins1,2, Chantal M. W. Tax3, Filip Szczepankiewicz2,4,5, Derek K. Jones3, and Daniel Topgaard1,2
1Physical Chemistry, Lund University, Lund, Sweden, 2Random Walk Imaging AB, Lund, Sweden, 3Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, United Kingdom, 4Harvard Medical School, Boston, MA, United States, 5Radiology, Brigham and Women’s Hospital, Boston, MA, United States

Due to their cubic-millimeter scale, white-matter diffusion MRI voxels are often heterogeneous, comprising not only multiple fibre bundles but also grey matter, cerebrospinal fluid, or pathological tissue. To tackle this problem, conventional approaches rely on assumptions regarding tissue properties. This work combines state-of-the-art diffusion-relaxation MR acquisition and processing methods to extract intra-voxel nonparametric 5D distributions of diffusion tensors and transverse relaxation rates $$$R_2$$$ without the use of limiting assumptions. Orientation-resolved (fibre-specific) means of isotropic diffusivities, diffusion anisotropies and $$$R_2$$$ values are then obtained via clustering within the orientation subspace of these 5D distributions.

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