gms | German Medical Science

Objective: Asymmetry of microstructure in brain has been demonstrated in fiber tracts using diffusion tensor imaging (DTI). Due to the inherent drawbacks of DTI such as limited capability of resolving fanning and crossing fibers, limited modeling of diffusion profiles and characteristics, more sophisticated approaches are needed such as diffusion kurtosis imaging (DKI). However, only a few studies investigated asymmetry of fiber tracts applying DKI. In this study, the effect of DTI vs. DKI regarding detection and evaluation of hemispheric asymmetry is evaluated.

Methods: 20 healthy (10 / 10 male / female, mean age 24 ± 1.2 years, 3 / 17 left-/right-handed) volunteers were included. For each volunteer DWI data (incorporating the possibility of analysis applying DTI as well as DKI) were acquired at a 3T MRI. Data was processed for DTI and DKI using the Diffusion Kurtosis Estimator (DKE) gaining diffusion parameters such as mean kurtosis (DKI_MK), fractional anisotropy (DTI_FA, DKI_FA), mean diffusivity (DTI_MD, DKI_MD). Data analysis was performed using Tract-based spatial statistics (TBSS) incorporating voxel-wise statistical analysis applying FSL Randomize. For nine major white matter tracts (CST = corticospinal tract, SLF = superior longitudinal fascicle, ILF = inferior longitudinal fascicle, UF uncinated fascicle, IFOF = inferior frontooccipital fascicle, CB = cingulate bundle, ATR = anterior thalamic radiation, Fmi = Forceps minor, Fma = Forceps major) a laterality index (LI) was calculated.

Results: Regarding DTI_FA and DTI_DKI leftward asymmetry was seen in CST, SLF, CB, ATR (LI: 0.19, 0.81. 0.31, 0.08), rightward asymmetry in Fmi, Fma, IFOF, UF (LI -0.56, -0.15, -0.27, -0.37), while the distribution of asymmetric regions was comparable between DTI and DKI. DTI_MD showed global rightward asymmetry in the Fmi, CB and ATR (p: 0.008, 0.008, 0.001) whereas DKI_MD revealed rightward asymmetry along the ILF and ATR (p: 0.024, 0.003). DKI_MK resulted in global leftward asymmetry for Fmi and ATR (p: 0.024, p: 0.002), as well as rightward asymmetry for ILF and SLF (p: 0.020, 0.041).

Conclusion: Only few previous studies have shown the location of asymmetric regions in fiber tracts. This study provides an overview of asymmetric regions in healthy young adults, especially within nine major white matter tracts. DTI_FA and DKI_FA are sensitive detecting hemispheric asymmetry. DKI_MK allows for a more accurate positional information on asymmetry not seen in DTI and DKI derived FA and MD.