Tractography and the connectome in neurosurgical treatment of gliomas: the premise, the progress, and the potential.

The ability of diffusion tensor MRI to detect the preferential diffusion of water in cerebral white matter tracts enables neurosurgeons to noninvasively visualize the relationship of lesions to functional neural pathways. Although viewed as a research tool in its infancy, diffusion tractography has evolved into a neurosurgical tool with applications in glioma surgery that are enhanced by evolutions in crossing fiber visualization, edema correction, and automated tract identification. In this paper the current literature supporting the use of tractography in brain tumor surgery is summarized, highlighting important clinical studies on the application of diffusion tensor imaging (DTI) for preoperative planning of glioma resection, and risk assessment to analyze postoperative outcomes. The key methods of tractography in current practice and crucial white matter fiber bundles are summarized. After a review of the physical basis of DTI and post-DTI tractography, the authors discuss the methodologies with which to adapt DT image processing for surgical planning, as well as the potential of connectomic imaging to facilitate a network approach to oncofunctional optimization in glioma surgery.

White matter correlates of disease duration in patients with temporal lobe epilepsy: updated review of literature.

BACKGROUND: Medial temporal lobe epilepsy (mTLE) has been associated with widespread white mater (WM) alternations in addition to mesial temporal sclerosis (MTS). Herein, we aimed to investigate the correlation between disease duration and WM structural abnormalities in mTLE using diffusion MRI (DMRI) connectometry approach. METHOD: DMRI connectometry was conducted on 24 patients with mTLE. A multiple regression model was used to investigate white matter tracts with microstructural correlates to disease duration, controlling for age and sex. DMRI data were processed in the MNI space using q-space diffeomorphic reconstruction to obtain the spin distribution function (SDF). The SDF values were converted to quantitative anisotropy (QA) and used in further analyses. RESULTS: Connectometry analysis identified impaired white matter QA of the following fibers to be correlated with disease duration: bilateral retrosplenial cingulum, bilateral fornix, right inferior longitudinal fasciculus (ILF), and genu of corpus callosum (CC) (FDR = 0.009). CONCLUSION: Our results were obtained from DMRI connectometry, which indicates the connectivity and the level of diffusion in nerve fibers rather just the direction of diffusion. Compared to previous studies investigating the correlation between duration of epilepsy and white matter integrity in mTLE patients, we detected broader and somewhat different associations in midline structures and component of limbic system. However, further studies with larger sample sizes are required to elucidate previous and current results.

Brain pathway differences between Parkinson's disease patients with and without REM sleep behavior disorder.

PURPOSE: REM (rapid eye movement) sleep behavior disorder (RBD) is characterized by increased muscle tone and violent limb movements and is a usual symptom of the early stages of Parkinson's disease (PD). PD patients with RBD represent faster motor and cognitive dysfunction progression. However, there are limited studies on possible structural brain changes underpinning this disorder. METHODS: Diffusion magnetic resonance imaging (DMRI) was used to assess whether microstructural abnormalities in the brain of 23 RBD positive PD are detectable compared to 31 RBD negative PD. DMRI scans were analyzed without a prior hypothesis. Diffusion MRI connectometry was used to carry out group analysis between age and gender matched PD patients with and without RBD. Diffusion MRI connectometry is based on spin distribution function (SDF) which quantifies the density of diffusing water and is more sensitive to psychological differences between groups. RESULTS: Patients with RBD positive showed microstructural white matter changes in the left and right cingulum, inferior front occipital fasciculus (IFOF), bilateral corticospinal tracts (CST), and middle cerebellar peduncles (MCPs), compared to patients without RBD. CONCLUSIONS: White matter alterations in the cingulum, IFOF regions, and corpus callosum might explain faster cognitive deterioration in PD patients with RBD, in terms of visual recognition and visuospatial dysfunction and executive function. Disturbed brain structural tissue markers in CST in PD + RBD patients, could be justified in the light of faster motor progression in these patients.

Diffusion MRI connectometry automatically reveals affected fiber pathways in individuals with chronic stroke.

Building a human connectome database has recently attracted the attention of many researchers, although its application to individual subjects has yet to be explored. In this study, we acquired diffusion spectrum imaging of 90 subjects and showed that this dataset can be used as a norm to examine pathways with deviant connectivity in individuals. This analytical approach, termed diffusion MRI connectometry, was realized by reconstructing patient data to a common stereotaxic space and calculating the percentile rank of the diffusion quantities with respect to those of the norm. The affected tracks were constructed with deterministic tractography using the local tract orientations with substantially low percentile ranks as seeds. To demonstrate the performance of the connectometry, we applied it to 7 patients with chronic stroke and compared the results with lesions shown on T2-weighted images, apparent diffusion coefficient (ADC) maps, and fractional anisotropy (FA) maps, as well as clinical manifestations. The results showed that the affected tracks revealed by the connectometry corresponded well with the stroke lesions shown on T2-weighted images. Moreover, while the T2-weighted images, as well as the ADC and FA maps, showed only the stroke lesions, connectometry revealed entire affected tracks, a feature that is potentially useful for diagnostic or prognostic evaluation. This unique capability may provide personalized information regarding the structural connectivity underlying brain development, plasticity, or disease in each individual subject.