Neurosurgical Applications of Magnetic Resonance Diffusion Tensor Imaging

Magnetic Resonance (MR) Diffusion Tensor Imaging (DTI) is a rapidly evolving technology that enables the visualization of neural fiber bundles, or white matter (WM) tracts. There are numerous neurosurgical applications for MR DTI including: (1) Tumor grading and staging; (2) Pre-surgical planning (determination of resectability, determination of surgical approach, identification of WM tracts at risk); (3) Intraoperative navigation (tumor resection that spares WM damage, epilepsy resection that spares WM damage, accurate location of deep brain stimulation structures); (4) Post-operative assessment and monitoring (identification of WM damage, identification of tumor recurrence). Limitations of MR DTI include difficulty tracking small and crossing WM tracts, lack of standardized data acquisition and post-processing techniques, and practical equipment, software, and timing considerations. Overall, MR DTI is a useful tool for planning, performing, and following neurosurgical procedures, and has the potential to significantly improve patient care. Technological improvements and increased familiarity with DTI among clinicians are next steps

Diffusion tensor tractograghy can affect treatment strategy to remove brain occupying mass lesions

Radical resection of a pathological lesion along with the preservation of eloquent cerebral tissue is the principle goal of neurosurgery. Brain lesions are usually diagnosed by conventional magnetic resonance imaging (MRI), but this method is unable to describe the relationship between lesions and neighboring specific white matter (WM) tracts. Diffusion tensor tractograghy (DTT) is a new sophisticated imaging modality to reveal the neural fibers and their relationships with lesions. In the current study we assess that how diffusion tensor tractograghy can affect on treatment planning in patients afflicted by different types of brain lesions. In this prospective observational study, eight patients with brain mass lesion underwent conventional brain MRI pulse sequences and DTT imaging with 1.5 Tesla system using 64 independent diffusion encoding directions between December 2011 to January 2013.Acquired images were assessed by the neuroradiologist and neurosurgeon. Finally, the treatment strategies were compared using data before and after the tractograghy. The treatment strategy in six patients changed from radiotherapy into the craniotomy by using tractograghy data, in one patient changed from radio surgery to craniotomy and in one patient, neurosurgeon preferred to avoid operation. As we can infer from this study, based on the tractograghy results, the treatment technique may be changed, and the treatment plan could be devised with more accuracy and in case of surgery, may lead to less post-operative neurological deficits and better outcome results

Advanced Application of Diffusion Kurtosis Imaging

Diffusion tensor imaging (DTI) has become a standard procedure in clinical routine as well as research as it enables the reconstruction and visualization of fiber tracts in the human brain. Due to the simplified assumption the tensor model – a Gaussian distribution of the diffusion – it typically fails to provide neither accurate spatial mapping nor quantification of crossing or kissing fibers. A clinically feasible development might be diffusion kurtosis imaging (DKI), an extension of DTI also integrating non-Gaussian distribution diffusion processes and thereby shall overcome some of its limitations. The potential DKI will be evaluated in case of the detection of the interhemispheric asymmetry of the white matter in healthy volunteers (n = 20), as well as the analysis of tumor-related impairments of fiber tracts and their correlation with neurological deficits in patients (n = 13) diagnosed with glioma. In order to analyze interhemispheric asymmetry across the whole brain, especially of nine large fiber tracts, tract-based spatial statistics (TBSS) analysis was performed using DTI- and DKI-based parameters, a laterality index was calculated for asymmetries and DTI- and DKI-based results were compared. With regard to fractional anisotropy as marker of integrity, asymmetry was found for all nine fiber tracts based on DTI and seven tracts based on DKI. For mean diffusivity, asymmetries were found for three (DTI) and two (DKI) fiber tracts. Regarding mean kurtosis, asymmetry was found in one tract. The interhemispheric asymmetry thereby varied in anatomical location as well as in cluster size. Only small parts of the tracts were affected. A comparison of DTI and DKI showed significantly higher fractional anisotropy and mean diffusivity based on DKI compared to DTI. Gender and handedness did not seem to have any influence. For the assessment of tumor-related changes of fiber tracts in patients diagnosed with glioma, especially in relation to pre-existing and postoperative neurological deficits (hemiparesis, aphasia), templates for the corticospinal tract and the arcuate fasciculus were created based on DTI- and DKI-derived parameters, respectively. The corticospinal tract and the arcuate fasciculus were reconstructed for each patient and the associated parametric maps were projected onto the templates. Based on this, alterations along the tracts could be identified and quantified. Alterations were found on fiber tracts regardless of the spatial proximity to the lesion. There was a correlation between alterations based on fractional anisotropy, mean diffusivity and mean kurtosis. Increased mean diffusivity was associated with alteration in mean kurtosis, a decreased fractional anisotropy was found concurrent with a likewise decreased mean kurtosis. In the case of pre-existing neurological deficits (hemiparesis, aphasia) with regard to the changes along the fiber tracts (corticospinal tract, left arcuate fasciculus), most often increased mean diffusivity and altered mean kurtosis was found. Applying this pattern for prediction of corresponding postoperative neurological deficits a sensitivity of 75.0% and a specificity of 87.5% was achieved. DKI seems to more precisely estimated and depict the underlying microstructure in comparison to DTI. Thereby, in pathological cases especially the mean kurtosis seems to be of special interest. A combination of DTI- and DKI based parameters, particularly with regard to its clinical usability and value, offers great potential in clinical routine

Multimodal Neuronavigation for Brain Tumor Surgery

The current neuronavigation techniques increase safety and surgeon confidence during neurosurgical procedure performance. However, its real usefulness remains in integrating multimodal information from advanced magnetic resonance imaging, as tractography (DTI), functional studies that evaluate motor and sensitive language, motor function (BOLD techniques with different paradigms), and nuclear medicine. At the operating room, the fusion of sonographic information acquired in real-time with the predefined plan increase the chance to achieve gross-total resection of primary brain tumors. Combining these different image modalities with brain mapping and motor stimulation information in selected cases is possible, increasing surgery safety. In this review, we present our experience with multimodal neuronavigation to treat brain tumors in pediatric patients