gms | German Medical Science

Objective: Nowadays, Diffusion Tensor Imaging based fiber tractography (DTI-FT), as available in commercial neuronavigation systems, is used to outline major white matter tracts. Nevertheless, the spatial extent of white matter tracts is often underestimated, due to diverse aspects of image acquisition and image processing. The diffusion tensor model itself, only modeling Gaussian distributed diffusion patterns, is not capable of distinguishing multi fiber populations, as present in at least one third of the brain. Further sophisticated diffusion models overcome this limitation, but are in most cases not applicable in clinical practice due to extensive image acquisition times. Diffusion Kurtosis Imaging (DKI), modeling Gaussian and non-Gaussian diffusion properties, uses multi-shell diffusion imaging and thereby only doubles image acquisition times to overcome limitations of the tensor model.

Methods: To evaluate the impact of DKI-FT vs. DTI-FT under clinical time constraints we analyzed fiber tractography results of the optic radiation, relevant for transmission of visual information to the visual cortex, using DTI-FT and DKI-FT in 20 healthy volunteers (mean age: 25.5± 2.1 years, male/female: 10/10) and 6 glioma patients. For every volunteer and patient MR image data was acquired at a 3T Trio MRI System (Siemens, Erlangen, Germany) including an echo planar imaging sequence with voxel size 2x2x2mm³, 30 diffusion encoding gradients, b-values: 0, 1000 and 2000 s/mm² and acquisition time of 9 minutes. Image data was processed using the Diffusion Kurtosis Estimator and TrackVis.

Results: Results differed significantly for DTI-FT and DKI-FT. In all volunteers DKI-FT outlined more solid and compound white matter tracts in contrast to DTI-FT with tract volumes of the left OR with 5.02±2.32cm³ vs. 3.69±2.40cm³ (p=0.005) and the right OR with 7.64±2.78cm³ vs. 5.74±3.10cm³ (p<0.001). On a single subject level in all cases DKI-FT outlined more solid tracts compared to DTI-FT with tract volumes widely varying according to the localization of the brain tumor.

Conclusion: DKI-FT shows promising results in order to visualize major white matter tracts in close vicinity to brain lesions with short imaging sequences applicable under clinical time constraints.