Investigation of Asleep versus Awake Motor Mapping in Resective Brain Surgery.

OBJECTIVE: To develop an asleep motor mapping paradigm for accurate detection of the corticospinal tract during glioma surgery and compare outcomes with awake patients undergoing glioma resection. METHODS: A consecutive cohort of adult patients undergoing craniotomy for suspected diffuse glioma with tumor in a perirolandic location who had awake or asleep cortical and subcortical motor mapping with positive areas of motor stimulation were assessed for postoperative extent of resection (EOR), permanent neurological deficit, and proximity of stimulation to diffusion tensor imaging-based corticospinal tract depiction on preoperative magnetic resonance imaging. Outcome data were compared between asleep and awake groups. RESULTS: In the asleep group, all 16 patients had improved or no change in motor function at last follow-up (minimum 3 months of follow-up). In the awake group, all 23 patients had improved function or no change at last follow-up. EOR was greater in the asleep group (mean [SD] EOR 88.71% [17.56%]) versus the awake group (mean [SD] EOR 80.62% [24.44%]), although this difference was not statistically significant (P = 0.3802). Linear regression comparing distance from stimulation to corticospinal tract in asleep (n = 14) and awake (n = 4) patients was r = -0.3759, R2 = 0.1413, P = 0.1853, and 95% confidence interval = -0.4453 to 0.09611 and r = 0.7326, R2 = 0.5367, P = 0.2674, and 95% confidence interval = -7.042 to 14.75, respectively. CONCLUSION: In this small patient series, asleep motor mapping using commonly available motor evoked potential hardware appears to be safe and efficacious in regard to EOR and functional outcomes.

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.

Amyloid, Vascular, and Resilience Pathways Associated with Cognitive Aging.

OBJECTIVE: To investigate the multifactorial processes underlying cognitive aging based on the hypothesis that multiple causal pathways and mechanisms (amyloid, vascular, and resilience) influence longitudinal cognitive decline in each individual through worsening brain health. METHODS: We identified 1,230 elderly subjects (aged ≥50 years) with an average of 4.9 years of clinical follow-up and with amyloid positron emission tomography, diffusion tensor imaging, and structural magnetic resonance imaging scans from the population-based Mayo Clinic Study of Aging. We examined imaging markers of amyloid and brain health (white matter microstructural integrity and cortical thinning), systemic vascular health preceding the imaging markers, and early to midlife intellectual enrichment to predict longitudinal cognitive trajectories. We used latent growth curve models for modeling longitudinal cognitive decline. RESULTS: All the pathways (amyloid, vascular, resilience) converged through their effects on cortical thinning and worsening cognition and together explained patterns in cognitive decline. Resilience and vascular pathways (aging process, sex differences, education/occupation, and systemic vascular health) had significant impact on white matter microstructural integrity. Education/occupation levels contributed to white matter integrity through systemic vascular health. Worsening white matter integrity contributed to significant cortical thinning and subsequently longitudinal cognitive decline. Baseline amyloidosis contributed to a significant proportion of cognitive decline that accelerated with longer follow-up times, and its primary impact was through cortical thinning. INTERPRETATION: We developed an integrated framework to help explain the dynamic and complex process of cognitive aging by considering key causal pathways. Such an approach is important for both better comprehension of cognitive aging processes and will aid in the development of successful intervention strategies. ANN NEUROL 2019;86:866-877.

White matter microstructure and cognitive outcomes in relation to neonatal inflammation in 6-year-old children born preterm.

BACKGROUND: Cognitive outcomes in preterm (PT) children have been associated with microstructural properties of white matter. PT children who experienced neonatal inflammatory conditions have poorer cognitive outcomes than those who did not. The goal of this study was to contrast white matter microstructure and cognitive outcomes after preterm birth in relation to the presence or absence of severe inflammatory conditions in the neonatal period. METHODS: PT children (n = 35), born at gestational age 22-32 weeks, were classified as either PT+ (n = 12) based on a neonatal history of inflammatory conditions, including bronchopulmonary dysplasia, necrotizing enterocolitis or culture positive sepsis, or PT- (n = 23) based on the absence of the three inflammatory conditions. Full term (FT) children (n = 43) served as controls. Participants underwent diffusion MRI and cognitive testing (intelligence, reading, and executive function) at age 6 years. The corpus callosum was segmented into 7 regions using deterministic tractography and based on the cortical projection zones of the callosal fibers. Mean fractional anisotropy (FA) and mean diffusivity (MD) were calculated for each segment. General linear models with planned contrasts assessed group differences in FA, MD and cognitive outcomes. Pearson correlations assessed associations of white matter metrics and cognitive outcome measures. RESULTS: FA was significantly lower and MD was significantly higher in PT+ compared to PT- or FT groups in multiple callosal segments, even after adjusting for gestational age. Executive function scores, but not intelligence or reading scores, were less favorable in PT+ than in PT- groups. Among the entire sample, occipital FA was significantly correlated with IQ (r = 0.25, p < 0.05), reading (r = 0.32, p < 0.01), and executive function (r = -0.28, p < 0.05) measures. Anterior frontal FA and superior parietal FA were significantly correlated with executive function (r = -0.25, r = 0.23, respectively, p < 0.05). CONCLUSIONS: We observed differences in the white matter microstructure of the corpus callosum and in the cognitive skills of 6-year-old PT children based on their history of neonatal inflammation. Neonatal inflammation is one medical factor that may contribute to variation in long-term neurobiological and neuropsychological outcomes in PT samples.

Relationship between the benefits of paraspinal mapping and diffusion tensor imaging and the increase of decompression levels determined by conventional magnetic resonance imaging in degenerative lumbar spinal stenosis.

BACKGROUND: In lumbar spinal stenosis (LSS), at most times, several levels are impaired and selecting the correct level remains a common problem for surgeons, as surgery remains invasive, and extended laminectomy may lead to secondary surgical complications. Therefore, helping to select the correct level may be useful for surgeons. The use of diffuse tensor imaging (DTI) and paraspinal mapping (PM) in addition to conventional magnetic resonance imaging (MRI) may be helpful (Chen et al., J Orthop Surg Res 11:47, 2016). However, with decompression levels determined by conventional magnetic resonance imaging (MRI) increasing, whether the benefits of reducing decompression level of conventional MRI + (DTI or PM) will be more obvious is unknown. METHODS: Reduced surgical levels that were different between levels determined by conventional MRI + (DTI or PM) and conventional MRI + neurogenic examination (NE) between groups were compared. Treatment outcome measures were performed at 2 weeks, 3 months, 6 months, and 12 months postoperatively. RESULTS: The reduced levels of three groups showed no statistically significant differences between each other except for two levels and four levels (two levels/three levels, p = 0.085; two levels/four levels, p = 0.039; three levels/ four levels, p = 0.506, respectively). CONCLUSIONS: With surgical levels determined by conventional MRI increasing, the benefits of DTI and PM will be uncertainly more obvious.

Diffusion-weighted imaging and diffusion tensor imaging as adjuncts to conventional MRI for the diagnosis and management of peripheral nerve sheath tumors: current perspectives and future directions.

Peripheral nerve sheath tumors (PNSTs) account for ~ 5% of soft tissue neoplasms and are responsible for a wide spectrum of morbidities ranging from localized neuropathy to fulminant metastatic spread and death. MR imaging represents the gold standard for identification of these neoplasms, however, current anatomic MR imaging markers do not reliably detect or differentiate benign and malignant lesions, and therefore, biopsy or excision is required for definitive diagnosis. Diffusion-weighted MR imaging (DWI) serves as a useful tool in the evaluation and management of PNSTs by providing functional information regarding the degree of diffusion, while diffusion tensor imaging (DTI) aids in determining the directional information of predominant diffusion and has been shown to be particularly useful for pre-operative planning of these tumors by delineating healthy and pathologic fascicles. The article focuses on these important neurogenic lesions, highlighting the current utility of diffusion MR imaging and future directions including computerized radiomic analysis. KEY POINTS: • Anatomic MRI is moderately accurate in differentiating benign from malignant PNST. • Diffusion tensor imaging facilitates pre-operative planning of PNSTs by depicting neuropathy and tractography. • Radiomics will likely augment current observer-based diagnostic criteria for PNSTs.

Different patterns of white matter changes after successful surgery of mesial temporal lobe epilepsy.

OBJECTIVES: To explore the dynamic changes of white matters following anterior temporal lobectomy (ATL) in mesial temporal lobe epilepsy (MTLE) patients who achieved seizure-free at two-year follow-up. METHODS: Diffusion tensor imaging (DTI) was obtained in ten MTLE patients at five serial time points: before surgery, three months, six months, 12 months and 24 months after surgery, as well as in 11 age- and sex-matched healthy controls at one time point. Regions with significant postoperative fractional anisotropy (FA) changes and their dynamic changes were confirmed by comparing all preoperative and postoperative data using Tract-Based Spatial Statistics (TBSS). RESULTS: After successful ATL, significant FA changes were found in widespread ipsilateral and contralateral white matter regions (P <.05, FWE correction). Ipsilateral external capsule, cingulum, superior corona radiate, body of corpus callosum, inferior longitudinal fasciculus, optic radiation and contralateral inferior cerebellar peduncle, inferior longitudinal fasciculus showed significant FA decrease at three months after surgery, without further changes. Ipsilateral superior cerebellar peduncle and contralateral corpus callosum, anterior corona radiate, external capsule, optic radiation showed significant FA decrease at three months follow up but increase later. Ipsilateral cerebral peduncle and contralateral middle cerebellar peduncle showed significant FA decrease at three months follow up, with further decrease after that. While ipsilateral posterior limb of internal capsule, retrolenticular part of internal capsule and contralateral posterior corona radiate showed significant FA increase after surgery. CONCLUSIONS: FA changes after successful ATL presented as four distinct patterns, reflecting different structural adaptions following epilepsy surgery. Some FA increases indicated the reversibility of preoperative diffusion abnormalities and the possibility of structural reorganization, especially in the contralateral hemisphere.

Overcoming Challenges of Cranial Nerve Tractography: A Targeted Review.

BACKGROUND: Diffusion imaging tractography caught the attention of the scientific community by describing the white matter architecture in vivo and noninvasively, but its application to small structures such as cranial nerves remains difficult. The few attempts to track cranial nerves presented highly variable acquisition and tracking settings. OBJECTIVE: To conduct and present a targeted review collecting all technical details and pointing out challenges and solutions in cranial nerve tractography. METHODS: A "targeted" review of the scientific literature was carried out using the MEDLINE database. We selected studies that reported how to perform the tractography of cranial nerves, and extracted the following: clinical context; imaging acquisition settings; tractography parameters; regions of interest (ROIs) design; and filtering methods. RESULTS: Twenty-one published articles were included. These studied the optic nerves in suprasellar tumors, the trigeminal nerve in neurovascular conflicts, the facial nerve position around vestibular schwannomas, or all cranial nerves. Over time, the number of MRI diffusion gradient directions increased from 6 to 101. Nine tracking software packages were used which offered various types of tridimensional display. Tracking parameters were disparately detailed except for fractional anisotropy, which ranged from 0.06 to 0.5, and curvature angle, which was set between 20° and 90°. ROI design has evolved towards a multi-ROI strategy. Furthermore, new algorithms are being developed to avoid spurious tracts and improve angular resolution. CONCLUSION: This review highlights the variability in the settings used for cranial nerve tractography. It points out challenges that originate both from cranial nerve anatomy and the tractography technology, and allows a better understanding of cranial nerve tractography.

Early postsurgical diffusivity metrics for prognostication of long-term pain relief after Gamma Knife radiosurgery for trigeminal neuralgia.

OBJECTIVE: Gamma Knife radiosurgery (GKRS) is an important treatment modality for trigeminal neuralgia (TN). Current longitudinal assessment after GKRS relies primarily on clinical diagnostic measures, which are highly limited in the prediction of long-term clinical benefit. An objective, noninvasive, predictive tool would be of great utility to advance the clinical management of patients. Using diffusion tensor imaging (DTI), the authors' aim was to determine whether early (6 months post-GKRS) target diffusivity metrics can be used to prognosticate long-term pain relief in patients with TN. METHODS: Thirty-seven patients with TN treated with GKRS underwent 3T MRI scans at 6 months posttreatment. Diffusivity metrics of fractional anisotropy, axial diffusivity, radial diffusivity, and mean diffusivity were extracted bilaterally from the radiosurgical target of the affected trigeminal nerve and its contralateral, unaffected nerve. Early (6 months post-GKRS) diffusivity metrics were compared with long-term clinical outcome. Patients were identified as long-term responders if they achieved at least 75% reduction in preoperative pain for 12 months or longer following GKRS. RESULTS: Trigeminal nerve diffusivity at 6 months post-GKRS was predictive of long-term clinical effectiveness, where long-term responders (n = 19) showed significantly lower fractional anisotropy at the radiosurgical target of their affected nerve compared to their contralateral, unaffected nerve and to nonresponders. Radial diffusivity and mean diffusivity, correlates of myelin alterations and inflammation, were also significantly higher in the affected nerve of long-term responders compared to their unaffected nerve. Nonresponders (n = 18) did not exhibit any characteristic diffusivity changes after GKRS. CONCLUSIONS: The authors demonstrate that early postsurgical target diffusivity metrics have a translational, clinical value and permit prediction of long-term pain relief in patients with TN treated with GKRS. Importantly, an association was found between the footprint of radiation and clinical effectiveness, where a sufficient level of microstructural change at the radiosurgical target is necessary for long-lasting pain relief. DTI can provide prognostic information that supplements clinical measures, and thus may better guide the postoperative assessment and clinical decision-making for patients with TN.

Diffusion Tensor Imaging in a Large Longitudinal Series of Patients With Cervical Spondylotic Myelopathy Correlated With Long-Term Functional Outcome.

BACKGROUND: Fractional anisotropy (FA) of the high cervical cord correlates with upper limb function in acute cervical cord injury. We investigated the correlation between preoperative FA at the level of maximal compression and functional recovery in a group of patients after decompressive surgery for cervical spondylotic myelopathy (CSM). OBJECTIVE: To determine the usefulness of FA as a biomarker for severity of CSM and as a prognostic biomarker for improvement after surgery. METHODS: Patients received diffusion tensor imaging (DTI) scans preoperatively. FA values of the whole cord cross-section at the level of maximal compression and upper cervical cord (C1-2) were calculated. Functional status was measured using the modified Japanese Orthopedic Association (mJOA) scale preoperatively and at follow-up up to 2 yr. Regression analysis between FA and mJOA was performed. DTI at C4-7 was obtained in controls. RESULTS: Forty-four CSM patients enrolled prior to decompression were compared with 24 controls. FA at the level of maximal compression correlated positively with preoperative mJOA score. Preoperative FA correlated inversely with recovery throughout the postoperative period. This was statistically significant at 12 mo postoperation and nearly so at 6 and 24 mo. Patients with preoperative FA <0.55 had a statistically significant difference in outcome compared to FA >0.55. CONCLUSION: In the largest longitudinal study of this kind, FA promises a valid biomarker for severity of CSM and postoperative improvement. FA is an objective measure of function and could provide a basis for prognosis. FA is particularly useful if preoperative values are less than 0.55.

Peripheral nerve diffusion tensor imaging: Overview, pitfalls, and future directions.

Diffusion tensor imaging (DTI) is a noninvasive magnetic resonance imaging (MRI) technique that measures the extent of restricted water diffusion and anisotropy in biological tissue. Although DTI has been widely applied in the brain, more recently researchers have used it to characterize nerve pathology in the setting of entrapment neuropathy, traumatic injury, and tumor. DTI artifacts are exacerbated when imaging off isocenter in the body. Anecdotally, the most significant artifacts in peripheral nerve DTI include magnetic field inhomogeneity, motion, incomplete fat suppression, aliasing, and distortion. High spatial resolution is also required to reliably evaluate smaller peripheral nerves. This article provides an overview of such technical issues, particularly when trying to apply DTI in the clinical setting, and offers potential solutions. LEVEL OF EVIDENCE: 5 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1171-1189.

Impact of intraoperative 3-T MRI with diffusion tensor imaging on hemispherectomy.

OBJECTIVE Hemispherectomy can produce remarkable seizure control of medically intractable hemispheric epilepsy in children, but some patients continue to have seizures after surgery. A frequent cause of treatment failure is incomplete surgical disconnection of the abnormal hemisphere. This study explores whether intraoperative 3-T MRI with diffusion tensor imaging (DTI) during hemispherectomy can identify areas of incomplete disconnection and allow complete disconnection during a single surgery. METHODS The charts of 32 patients with epilepsy who underwent hemispherectomy between January 2012 and July 2014 at the Florida Hospital for Children were reviewed. Patients were grouped as having had curative or palliative hemispherectomy. To assess the completeness of disconnection when the surgeon considered the operation completed, intraoperative 3-T MRI-DTI was performed. If incomplete disconnection was identified, additional surgery was performed until MRI-DTI sequences confirmed satisfactory disconnection. Seizure outcome data were collected via medical records at last follow-up. RESULTS Of 32 patients who underwent hemispherectomy, 23 had curative hemispherectomy and 9 had palliative hemispherectomy. In 11 of 32 surgeries, the first intraoperative MRI-DTI sequences suggested incomplete disconnection and additional surgery followed by repeat MRI-DTI was performed. Complete disconnection was accomplished in 30 of 32 patients (93.8%). Two of 32 disconnections (6.3%) were incomplete on postoperative imaging. Cross-sectional results showed that 21 of 23 patients (91.3%) who had curative hemispherectomy remained free of seizures (International League Against Epilepsy Class 1) at a median follow-up of 1.7 years (range 0.4-2.9 years). The longitudinal seizure freedom after curative hemispherectomy was 95.2% (SE 0.05) at 6 months, 90.5% (SE 0.06) at 1 year, and 90.5% (SE 0.05) at 2 years. CONCLUSIONS Intraoperative 3-T MRI-DTI sequences can identify incomplete disconnection during hemispherectomy and allow higher rates of complete disconnection in a single surgery. Higher rates of complete disconnection seem to achieve better seizure-free outcome following modified functional hemispherectomy.

Vulnerability of white matter to insult during childhood: evidence from patients treated for medulloblastoma.

OBJECTIVE Craniospinal irradiation damages the white matter in children treated for medulloblastoma, but the treatment-intensity effects are unclear. In a cross-sectional retrospective study, the effects of treatment with the least intensive radiation protocol versus protocols that delivered more radiation to the brain, in addition to the effects of continuous radiation dose, on white matter architecture were evaluated. METHODS Diffusion tensor imaging was used to assess fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity. First, regional white matter analyses and tract-based spatial statistics were conducted in 34 medulloblastoma patients and 38 healthy controls. Patients were stratified according to those treated with 1) the least intensive radiation protocol, specifically reduced-dose craniospinal irradiation plus a boost to the tumor bed only (n = 17), or 2) any other dose and boost combination that delivered more radiation to the brain, which was also termed the "all-other-treatments" group (n = 17), and comprised patients treated with standard-dose craniospinal irradiation plus a posterior fossa boost, standard-dose craniospinal irradiation plus a tumor bed boost, or reduced-dose craniospinal irradiation plus a posterior fossa boost. Second, voxel-wise dose-distribution analyses were conducted on a separate cohort of medulloblastoma patients (n = 15). RESULTS The all-other-treatments group, but not the reduced-dose craniospinal irradiation plus tumor bed group, had lower fractional anisotropy and higher radial diffusivity than controls in all brain regions (all p < 0.05). The reduced-dose craniospinal irradiation plus tumor bed boost group had higher fractional anisotropy (p = 0.05) and lower radial diffusivity (p = 0.04) in the temporal region, and higher fractional anisotropy in the frontal region (p = 0.04), than the all-other-treatments group. Linear mixed-effects modeling revealed that the dose and age at diagnosis together 1) better predicted fractional anisotropy in the temporal region than models with either alone (p < 0.005), but 2) did not better predict fractional anisotropy in comparison with dose alone in the occipital region (p > 0.05). CONCLUSIONS Together, the results show that white matter damage has a clear association with increasing radiation dose, and that treatment with reduced-dose craniospinal irradiation plus tumor bed boost appears to preserve white matter in some brain regions.

[Functional brain imaging]. / Funktionelle Hirnbildgebung.

METHOD: Functional magnetic resonance imaging (fMRI) is a non-invasive method that has become one of the major tools for understanding human brain function and in recent years has also been developed for clinical applications. PERFORMANCE: Changes in hemodynamic signals correspond to changes in neuronal activity with good spatial and temporal resolution in fMRI. Using high-field MR systems and increasingly dedicated statistics and postprocessing, activated brain areas can be detected and superimposed on anatomical images. Currently, fMRI data are often combined in multimodal imaging, e. g. with diffusion tensor imaging (DTI) sequences. This method is helping to further understand the physiology of cognitive brain processes and is also being used in a number of clinical applications. In addition to the blood oxygenation level-dependent (BOLD) signals, this article deals with the construction of fMRI investigations, selection of paradigms and evaluation in the clinical routine. Clinically, this method is mainly used in the planning of brain surgery, analyzing the location of brain tumors in relation to eloquent brain areas and the lateralization of language processing. PRACTICAL RECOMMENDATIONS: As the BOLD signal is dependent on the strength of the magnetic field as well as other limitations, an overview of recent developments is given. Increases of magnetic field strength (7 T), available head coils and advances in MRI analytical methods have led to constant improvement in fMRI signals and experimental design. Especially the depiction of eloquent brain regions can be done easily and quickly and has become an essential part of presurgical planning.

Multiparametric MR Imaging in the Assessment of Brain Tumors.

Functional MR imaging methods make possible the quantification of dynamic physiologic processes that occur in the brain. Moreover, the use of these advanced imaging techniques in the setting of oncologic treatment of the brain is widely accepted and has found worldwide routine clinical use.

Effects of vascular risk factors and APOE ε4 on white matter integrity and cognitive decline.

OBJECTIVE: To investigate the effects of vascular risk factors and APOE status on white matter microstructure, and subsequent cognitive decline among older people. METHODS: This study included 241 participants (age 60 years and older) from the population-based Swedish National Study on Aging and Care in Kungsholmen in central Stockholm, Sweden, who were free of dementia and stroke at baseline (2001-2004). We collected data through interviews, clinical examinations, and laboratory tests. We measured fractional anisotropy (FA) and mean diffusivity (MD) on diffusion tensor imaging, and estimated volume of white matter hyperintensities using automatic segmentation. We assessed global cognitive function with the Mini-Mental State Examination at baseline and at 3- and/or 6-year follow-up. We analyzed the data using multivariate linear regression and linear mixed models. RESULTS: Heavy alcohol consumption, hypertension, and diabetes were significantly associated with lower FA or higher MD (p < 0.05). When aggregating heavy alcohol consumption, hypertension, and diabetes together with current smoking, having an increasing number of these 4 factors concurrently was associated with decreasing FA and increasing MD (ptrend < 0.01), independent of white matter hyperintensities. Vascular risk factors and APOE ε4 allele interacted to negatively affect white matter microstructure; having multiple (≥2) vascular factors was particularly detrimental to white matter integrity among APOE ε4 carriers. Lower tertile of FA and upper tertile of MD were significantly associated with faster Mini-Mental State Examination decline. CONCLUSIONS: Vascular risk factors are associated with reduced white matter integrity among older adults, which subsequently predicted faster cognitive decline. The detrimental effects of vascular risk factors on white matter microstructure were exacerbated among APOE ε4 carriers.

Advanced 3-dimensional planning in neurosurgery.

During the past decades, medical applications of virtual reality technology have been developing rapidly, ranging from a research curiosity to a commercially and clinically important area of medical informatics and technology. With the aid of new technologies, the user is able to process large amounts of data sets to create accurate and almost realistic reconstructions of anatomic structures and related pathologies. As a result, a 3-diensional (3-D) representation is obtained, and surgeons can explore the brain for planning or training. Further improvement such as a feedback system increases the interaction between users and models by creating a virtual environment. Its use for advanced 3-D planning in neurosurgery is described. Different systems of medical image volume rendering have been used and analyzed for advanced 3-D planning: 1 is a commercial "ready-to-go" system (Dextroscope, Bracco, Volume Interaction, Singapore), whereas the others are open-source-based software (3-D Slicer, FSL, and FreesSurfer). Different neurosurgeons at our institution experienced how advanced 3-D planning before surgery allowed them to facilitate and increase their understanding of the complex anatomic and pathological relationships of the lesion. They all agreed that the preoperative experience of virtually planning the approach was helpful during the operative procedure. Virtual reality for advanced 3-D planning in neurosurgery has achieved considerable realism as a result of the available processing power of modern computers. Although it has been found useful to facilitate the understanding of complex anatomic relationships, further effort is needed to increase the quality of the interaction between the user and the model.

Diffusion tensor imaging and neuromodulation: DTI as key technology for deep brain stimulation.

Diffusion tensor imaging (DTI) is more than just a useful adjunct to invasive techniques like optogenetics which recently have tremendously influenced our understanding of the mechanisms of deep brain stimulation (DBS). In combination with other technologies, DTI helps us to understand which parts of the brain tissue are connected to others and which ones are truly influenced with neuromodulation. The complex interaction of DBS with the surrounding tissues-scrutinized with DTI-allows to create testable hypotheses that can explain network interactions. Those interactions are vital for our understanding of the net effects of neuromodulation. This work naturally was first done in the field of movement disorder surgery, where a lot of experience regarding therapeutic effects and only a short latency between initiation of neuromodulation and alleviation of symptoms exist. This chapter shows the journey over the past 10 years with first applications in DBS toward current research in affect regulating network balances and their therapeutic alterations with the neuromodulation technology.