Neuroscientists interested in the study of white matter brain asymmetry.The brain hemispheres of the healthy human are asymmetric in terms of function and structure¹. During normal development, the degree of asymmetry varies for the different brain areas as found, in particular, by diffusion tensor imaging (DTI)². Thus far, to explore the brain microstructural asymmetry, researchers have mainly focused on parameters such as fractional anisotropy (FA) using conventional DTI. The aim of this study is to investigate what complimentary information can be obtained regarding brain microstructural asymmetry using diffusion kurtosis imaging (DKI)³, a more advanced extension of DTI that allows one to assess the level of diffusional non Gaussianity. The work has been performed on a group of adults and a group of children. Moreover, we investigated the differences between these two groups in order to elucidate the change of asymmetry during development.Healthy, right-handed adults (N=20) and children (N=21) underwent DKI in a 3T MRI scanner (Siemens MAGNETOM Tim-Trio). A double-refocused diffusion-weighted spin-echo EPI sequence was used with three b-values = 0, 1000 and 2800 s/mm² and 30 gradient directions. Nonlinear coregistration to the FA map from the John Hopkins University (JHU)⁴ was carried out using in-house Matlab scripts. Evaluation of the following DKI scalar parameters was performed with the help of the ExploreDTI toolkit⁵: FA, MD, axial (AD) and radial diffusivities (RD), kurtosis anisotropy (KA), mean (MK), axial (AK) and radial kurtoses (RK). Average over anatomical regions of the DKI metrics was performed using the JHU atlas (18 regions-of-interest (ROI) - 9 left and 9 right, forceps major and minor were excluded). The asymmetry index (AI) was evaluated for all DKI parameters and all anatomies as AI = 2(L-R)/(L+R). We used a one-sample t-test to examine hemispheric differences in each group and applied Bonferroni corrections for multiple comparisons. Then, in order to assess the asymmetry during development, we compared the AI in adults and children using a two-sample t-test for those anatomical regions where both group showed significant laterality.Leftward (L>R) FA asymmetry in Cg and rightward (R>L) FA asymmetry in Ch, SLF, UF and SLF_temp were observed for both adults and children groups. Besides, rightward FA asymmetry in CST was found for children only. In Cg, Ch and SLF the AI of AK showed values around two times higher than AI of FA for both groups. In ATR, IFOF and ILF, FA asymmetry was non-significant but some other parameters showed significant laterality. However, none of the anatomic regions exhibited asymmetries of all studied metrics simultaneously. Cg, the fibre bundle whose FA laterality is often reported in DTI studies⁶, showed significant asymmetry of 6 parameters studied (FA, RD, AK, MK, KA, and RK), see Table 1. A between-group comparison (Fig.1) has shown significantly higher leftward laterality in Cg (on MK, p<0.010 and RK, p<0.017) and SLF (on MD, p<0.027 and AD, p<0.007) and rightward laterality in SLF_temp (on AD, p<0.016, MK, p<0.019 and RK, p<0.040).Generally, reports on hemispheric asymmetries are not consistent across the literature. Our results are generally in line with earlier DTI works reporting rightward FA asymmetry⁷ in CST and leftward FA asymmetry in Cg¹ in Children but no FA asymmetry in Cg observed in adults⁸. We discuss additional information provided by diffusional kurtosis parameters in the context of a) microstructural features underlying asymmetry (such as those, leading to enhanced AK, RK, and MK in the left Cg) and b) subtle microstructural changes ongoing beyond late childhood.We have shown that DKI parameters can provide more comprehensive information on brain asymmetry. The degree of asymmetry for some fibres was found to be much higher for children than for adults.ATR: Anterior thalamic radiation; CST: Corticospinal tract; Cg: Cingulum (cingulate gyrus); Ch: Cingulum (hippocampus); IFOF: Inferior fronto-occipital fasciculus; ILF: Inferior longitudinal fasciculus; SLF: Superior longitudinal fasciculus; UF: Uncinate fasciculus; SLF_temp: Superior longitudinal fasciculus in temporal part.