Reconstruction Of The Language- And Motor-related Fiber Tracts For Neurosurgical Planning Using Two-tensor Unscented Kalman Filter Tractography

BackgroundDiffusion imaging tractography is increasingly used to trace critical fiber tracts in brain tumor patients to reduce the risk of post-operative neurologic deficit. However, the effects of peritumoral edema and crossing fibers pose a challenge to conventional tractography using the standard diffusion tensor model. The aim of this study was to present a novel technique using a two-tensor unscented Kalman filter (UKF) algorithm to track the arcuate fasciculus (AF) and corticospinal tract (CST) by tracking through regions of peritumoral edema and crossing fibers in brain tumor patients.Methods:In this thesis, we designed three studies to define the performance of two-tensor UKF tractography in tracing the language-and motor related fiber tracts for neurosurgical planning.In study 1, ten right-handed patients with left-sided brain tumors in the vicinity of language-related cortex and evidence of significant peritumoral edema were retrospectively selected for the study. All patients underwent 3-Tesla magnetic resonance imaging (MRI) including a diffusion-weighted data set with 31 directions. Fiber tractography was performed using both single-tensor streamline and two-tensor UKF tractography. A two-regions-of-interest approach was applied to perform the delineation of the AF. Results from the two different tractography algorithms were compared visually and quantitatively.In study 2, ten patients with brain tumors in the vicinity of motor cortex and evidence of significant peritumoral edema were retrospectively selected for the study. All patients underwent 3-TesIa magnetic resonance imaging (MRI) including functional MRI (fMRI) and a diffusion-weighted data set with 31 directions. Fiber tracking was performed using both single-tensor streamline and two-tensor UKF tractography methods. A two-regions-of-interest approach was used to delineate the CST. Results from the two tractography methods were compared visually and quantitatively. fMRI was applied to identify the functional fiber tracts.In study 3, we retrospectively selected eight consecutive brain tumor patients for the study. All patients underwent 3-Tesla magnetic resonance imaging (MRI) including a diffusion-weighted scan with 31 directions. We designed three experiments using different seeding methods and fiber selection strategies to compare the performance of the two algorithms. In each experiment, fiber tracking of the CST was performed in all datasets using both CSD and two-tensor UKF tractography. The evaluation of the CST was based on visual inspection and quantitative measurement of fiber tracts.Results:In study 1, our results showed that, using single-tensor streamline tractography, the AF appeared disrupted in four patients and contained few fibers in the remaining six patients. Two-tensor UKF tractography delineated an AF that traversed edematous brain areas in all patients. The volume of the AF was significantly larger on two-tensor UKF (11685.420 ± 6970.921, mean ± SD) than on single-tensor streamline (2201.850 ± 2294.674, mean ± SD) tractography (p< 0.05).In study 2, our results showed that single-tensor streamline tractography underestimated the extent of tracts running through the edematous areas and could only track the medial projections of the CST. In contrast, two-tensor UKF tractography tracked fanning projections of the CST despite peritumoral edema and crossing fibers. The two-tensor UKF tractography delineated tracts that were closer to motor fMRI activations,and it was more sensitive than single-tensor streamline tractography to define the tracts directed to the motor sites. The volume of the CST was significantly larger on two-tensor UKF (79858.780 ± 13719.452, mean ± SD) than on single-tensor streamline (7396.180 ± 2662.399, mean ± SD) tractography (p< 0.05).In study 3, our results showed that using whole brain seeding combined with anatomical regions of interest (ROIs) or functional MRI maps for fiber selection, two-tensor UKF tractography outperformed CSD tractography in tracing the CST. In contrast, when using brainstem ROIs as seed regions for fiber tracking and functional MRI maps as target ROIs or vice versa, CSD tractography outperformed two-tensor UKF tractography. We found that false positive fiber tracts were more likely in CSD tractography. The fiber tracts trajectories produced by two-tensor UKF tractography were smoother than those produced by CSD. Furthermore, we found that the visualization of tractography results from two-tensor UKF tractography in 3D Slicer was better than from CSD tractography in MRview for neurosurgical planning.Conclusions:In study 1, we showed two-tensor UKF tractography provides the ability to trace a larger volume AF than single-tensor streamline tractography in the setting of peritumoral edema in brain tumor patients.In study 2, we showed that two-tensor UKF tractography tracks the CST better than single-tensor streamline tractography in the setting of peritumoral edema and crossing fibers in brain tumor patients.In study 3, we showed that the differences between CSD and two-tensor UKF tractography in tracing CST in patients with brain lesions varied according to the seeding methods and fiber selection strategies. In general, two-tensor UKF tractography is potentially better than CSD tractography in tracing the CST for neurosurgical planning.In general, we showed that two-tensor unscented Kalman filter tractography provided the ability to trace the language- and motor-related fiber tracts better than both single-tensor streamline and CSD tractography algorithms for neurosurgical planning and had the potential to be used in clinical practice.