Direct Evidence for Decreased Intra-Axonal Diffusivity in Ischemic Human Stroke

Els Fieremans¹, Jens H. Jensen², Edward S. Hui², Dmitry S. Novikov¹, Ali Tabesh², Leonardo Bonilha², Joseph A. Helpern²

The decrease of the water diffusion coefficient in ischemic stroke provides a sensitive and reliable diagnostic tool. However, the underlying biophysical mechanisms for the diffusion drop are still not fully understood. In this study, we characterize changes in the white matter microstructure in human subacute stroke by applying a recently developed white matter model for diffusional kurtosis imaging, which yields estimates for the intra-axonal and extra-axonal diffusivities and for the axonal water fraction. A large change of 55% is observed in the intra-axonal diffusivity, consistent with axonal beading as a primary mechanism underlying the diffusion drop associated with ischemia.