gms | German Medical Science

Objective: Diffusion Tensor Imaging (DTI) and DTI-based fiber tractography (DTI-FT) has become a routine tool in multimodality neuronavigation to outline major white matter tracts non-invasively. The spatial extent of white matter tracts is commonly underestimated, leading to larger safety margins and thereby in case of doubt leading to reduced extent of tumor resection. DTI and DTI-FT is thereby largely dependent on image quality being affected by e.g. different artifacts during data acquisition. For example susceptibility artifacts occur as non-linear distortions within the image data in phase-encoding direction leading to a shift of white matter tracts and higher uncertainty in location and spatial extent. Correction of susceptibility artifacts can be achieved applying inversed phase-enconding directions during image acquisition and calculation of according deformation maps.

Methods: To evaluate the impact of susceptibility artifact correction on the reconstruction of the corticospinal tract (CST) diffusion imaging data of 20 healthy volunteers (mean age: 25.50± 2.06, male/female: 10/10) 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 phase encoding directions anterior-posterior and posterior-anterior. Image data was processed using the SPM Toolbox ACID for artifact correction and the Diffusion Toolkit and TrackVis for tensor calculation and fiber tractography.

Results: Without artifact correction mean fiber bundle volumes of 2.32±1.15cm³ (right CST) and 3.15±1.32cm³ (left CST) were achieved in contrast to significantly larger fiber bundle volumes of 3.93±2.01cm³ (right CST, p<0.001) and 4.54±2.19cm³ (left CST, p=0.003) with application of artifact correction. Comparing localization of white matter tracts using a measure of spatial overlap (Dice Coefficient) severe differences were seen for the left CST with a spatial overlap of 54.93±21.74% and 51.24±23.55% for the right CST.

Conclusion: Susceptibility artifact correction leads to a reconstruction of significantly larger fiber bundles in comparison to fiber tractography without susceptibility artifact correction. Distortion due to local susceptibility artifact can be at least in part be compensated for using the artifact correction toolbox. Achieved equalization of images leads to a change in location (shift) and spatial extent in the corticospinal tract.