Axonal Spectrum Imaging (AxSI): In-Vivo mapping of axonal diameter distributions in the human brain

Abstract In this paper we demonstrate a generalized and simplified pipeline called axonal spectrum imaging (AxSI) for in-vivo estimation of axonal characteristics in the human brain. Whole-brain estimation of the axon diameter, in-vivo and non-invasively, across all fiber systems will allow exploring uncharted aspect of brain structure and function relations. While axon diameter mapping is important in and of itself, its correlation with conduction velocity will allow, for the first time, the explorations of information transfer mechanisms within the brain. We demonstrate various well-known aspects of axonal morphometry (e.g., the corpus callosum axon diameter variation) as well as other aspects that are less explored (e.g., axon diameter-based separation of the superior longitudinal fascicules into segments). Moreover, we have created an MNI based mean axon diameter maps over the entire brain for a large cohort of subjects providing the reference basis for future studies exploring relation between axon properties, brain function, physiology and behavior.