Towards a better understanding of the meaning of diffusion kurtosis in the human briain. Insights from theoretical models and simulations

Abstract

DKI is an emerging technique based on non-Gaussian water diffusion analysis. A better explanation of the meaning of kurtosis in terms of features of microstructural anatomy would make DKI more concrete and accessible for clinicians. This work aims at a better understanding on the meaning of kurtosis in the human brain. A literature study is performed on possible causes of changes in kurtosis according to some popular diffusion models. First we review some of these models and their validity. Second we give an overview of anatomical links between diffusion models and kurtosis metrics that are implied by the reviewed models. Tortuousity differences, exchange, axon/neurite fraction, axon radius, neurite orientation distribution, intrinsic axon/neurite diffusivity, axon bending, bulging, breaking and crimping are in this way found to affect kurtosis metrics. Axon orientation dispersion, CSF contamination, astrocytes, trapped water and axon undulation could possibly also affect kurtosis metrics. Several rules of thumb are stated which provides anatomical explanations for a positively or negatively observed change in a kurtosis metric