New insight into the contrast in diffusional kurtosis images: Does it depend on magnetic susceptibility?

Abstract

Purpose In this MRI study, diffusional kurtosis imaging (DKI) and T2∗ multiecho relaxometry were measured from the white matter (WM) of human brains and correlated with each other, with the aim of investigating the influence of magnetic-susceptibility (ΔχH2O-TISSUE) on the contrast. Methods We focused our in vivo analysis on assessing the dependence of mean, axial, and radial kurtosis (MK, K-, K≤), as well as DTI indices on ΔχH2O-TISSUE (quantified by T2∗) between extracellular water and WM tissue molecules. Moreover, Monte Carlo (MC) simulations were used to elucidate experimental data. Results A significant positive correlation was observed between K≤, MK and R2∗= 1/T2∗, suggesting that ΔχH2O-TISSUE could be a source of DKI contrast. In this view, K≤ and MK-map contrasts in human WM would not just be due to different restricted diffusion processes of compartmentalized water but also to local ΔχH2O-TISSUE. However, MC simulations show a strong dependence on microstructure rearrangement and a feeble dependence on ΔχH2O-TISSUE of DKI signal. Conclusion Our results suggests a concomitant and complementary existence of multi-compartmentalized diffusion process and ΔχH2O-TISSUE in DKI contrast that might explain why kurtosis contrast is more sensitive than DTI in discriminating between different tissues. However, more realistic numerical simulations are needed to confirm this statement. Magn Reson Med 73:2015-2024, 2015.