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Abstract #2619

Undulating and crossing axons in the corpus callosum may explain the overestimation of axon diameters with ActiveAx

Tim B Dyrby 1 , Mark Burke 2 , Daniel C Alexander 3 , and Maurice Ptito 1,4

1 Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark, 2 Departments of Physiology and Biophysics, Howard University, Washington, United States, 3 Centre for Medical Image Computing, University College London, London, United Kingdom, 4 School of Optometry, University of Montreal, Montreal, Canada

Axon diameter (AD) estimates from diffusion-weighted imaging (DWI) is known being overestimated when compared with electron microscopy (EM). Mean AD in ten regions across the corpus callosum (CC) was obtained from painstaking EM. The ADs from DWI using ActiveAx method were found overestimated but similar AD contrast as with EM was observed across CC. With classical histology, undulating axons was observed throughout CC, and crossing axons in genu also. Undulation leads to larger cross-sectional area than straight axons hence AD overestimation. This suggests that macroscopic features as undulating axons can explain the overestimation we observed from AD estimates using DWI.

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