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Abstract #0716

Microscopic anisotropy in gray matter is evidence of myelinated axons but not dendrites? An in vivo study using diffusion MRI with variable shape of the b-tensor.

Björn Lampinen1, Filip Szczepankiewicz1, Mikael Novén2, Carl-Fredrik Westin3, Elisabet Englund4, Johan Mårtensson5, and Markus Nilsson6

1Clinical Sciences Lund, Medical Radiation Physics, Lund University, Lund, Sweden, 2Centre for Languages and Literature, Lund University, Lund, Sweden, 3Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, 4Clinical Sciences Lund, Oncology and Pathology, Lund University, Lund, Sweden, 5Department of Psychology, Faculty of Social Science, Lund University, Lund, Sweden, 6Clinical Sciences Lund, Radiology, Lund University, Lund, Sweden

Microscopic anisotropy was measured in vivo using a novel tensor-valued diffusion encoding approach. In gray matter, the microscopic anisotropy was generally low, but its variation corresponded well to known differences in myelination. We hypothesize that myelinated axons cause microscopic diffusion anisotropy but that the contribution from dendrites is negligible. This hypothesis is supported by comparisons with independent myelin assessments using T1W/T2W-ratios, T2-mapping, and myelin stains from histology. We also demonstrate that the “neurite density index” detected by NODDI is less sensitive to these changes, and why NODDI cannot map the neurite density accurately.

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