Comparative validation of automated presurgical tractography based on constrained spherical deconvolution and diffusion tensor imaging with direct electrical stimulation.

OBJECTIVES: Accurate presurgical brain mapping enables preoperative risk assessment and intraoperative guidance. This cross-sectional study investigated whether constrained spherical deconvolution (CSD) methods were more accurate than diffusion tensor imaging (DTI)-based methods for presurgical white matter mapping using intraoperative direct electrical stimulation (DES) as the ground truth. METHODS: Five different tractography methods were compared (three DTI-based and two CSD-based) in 22 preoperative neurosurgical patients undergoing surgery with DES mapping. The corticospinal tract (CST, N = 20) and arcuate fasciculus (AF, N = 7) bundles were reconstructed, then minimum distances between tractograms and DES coordinates were compared between tractography methods. Receiver-operating characteristic (ROC) curves were used for both bundles. For the CST, binary agreement, linear modeling, and posthoc testing were used to compare tractography methods while correcting for relative lesion and bundle volumes. RESULTS: Distance measures between 154 positive (functional response, pDES) and negative (no response, nDES) coordinates, and 134 tractograms resulted in 860 data points. Higher agreement was found between pDES coordinates and CSD-based compared to DTI-based tractograms. ROC curves showed overall higher sensitivity at shorter distance cutoffs for CSD (8.5 mm) compared to DTI (14.5 mm). CSD-based CST tractograms showed significantly higher agreement with pDES, which was confirmed by linear modeling and posthoc tests (PFWE < .05). CONCLUSIONS: CSD-based CST tractograms were more accurate than DTI-based ones when validated using DES-based assessment of motor and sensory function. This demonstrates the potential benefits of structural mapping using CSD in clinical practice.

Visualization of iron-rich subcortical structures in non-human primates in vivo by quantitative susceptibility mapping at 3T MRI.

Magnetic resonance imaging (MRI) is now an essential tool in the field of neuroscience involving non-human primates (NHP). Structural MRI scanning using T1-weighted (T1w) or T2-weighted (T2w) images provides anatomical information, particularly for experiments involving deep structures such as the basal ganglia and cerebellum. However, for certain subcortical structures, T1w and T2w image contrasts are insufficient for their detection of important anatomical details. To better visualize such structures in the macaque brain, we applied a relatively new method called quantitative susceptibility mapping (QSM), which enhances tissue contrast based on the local tissue magnetic susceptibility. The QSM significantly improved the visualization of important structures, including the ventral pallidum (VP), globus pallidus external and internal segments (GPe and GPi), substantia nigra (SN), subthalamic nucleus (STN) in the basal ganglia and the dentate nucleus (DN) in the cerebellum. We quantified this the contrast enhancement by systematically comparing of contrast-to-noise ratios (CNRs) of QSM images relative to the corresponding T1w and T2w images. In addition, QSM values of some structures were correlated to the age of the macaque subjects. These results identify the QSM method as a straightforward and useful tool for clearly visualizing details of subcortical structures that are invisible with more traditional scanning sequences.

Localization accuracy of a common beamformer for the comparison of two conditions.

The linearly constrained minimum variance beamformer is frequently used to reconstruct sources underpinning neuromagnetic recordings. When reconstructions must be compared across conditions, it is considered good practice to use a single, "common" beamformer estimated from all the data at once. This is to ensure that differences between conditions are not ascribable to differences in beamformer weights. Here, we investigate the localization accuracy of such a common beamformer. Based on theoretical derivations, we first show that the common beamformer leads to localization errors in source reconstruction. We then turn to simulations in which we attempt to reconstruct a (genuine) source in a first condition, while considering a second condition in which there is an (interfering) source elsewhere in the brain. We estimate maps of mislocalization and assess statistically the difference between "standard" and "common" beamformers. We complement our findings with an application to experimental MEG data. The results show that the common beamformer may yield significant mislocalization. Specifically, the common beamformer may force the genuine source to be reconstructed closer to the interfering source than it really is. As the same applies to the reconstruction of the interfering source, both sources are pulled closer together than they are. This observation was further illustrated in experimental data. Thus, although the common beamformer allows for the comparison of conditions, in some circumstances it introduces localization inaccuracies. We recommend alternative approaches to the general problem of comparing conditions.

Language Mapping With Magnetoencephalography: An Update on the Current State of Clinical Research and Practice With Considerations for Clinical Practice Guidelines.

Numerous studies have shown that language processing is not limited to a few brain areas. Visual or auditory stimuli activate corresponding cortical areas, then memory identifies the word or image, Wernicke's and Broca's areas support the processing for either reading/listening or speaking and many areas of the brain are recruited. Determining how a normal person processes language helps clinicians and scientist to understand how brain pathologies such as tumor or stroke can affect changes in language processing. Patients with epilepsy may develop atypical language organization. Over time, the chronic nature of epileptic activity, or changes from a tumor or stroke, can result in a shift of language processing area from the left to the right hemisphere, or re-routing of language pathways from traditional to non-traditional areas within the dominant left hemisphere. It is important to determine where these language areas are prior to brain surgery. MEG evoked responses reflecting cerebral activation of receptive and expressive language processing can be localized using several different techniques: Single equivalent current dipole, current distribution techniques or beamformer techniques. Over the past 20 years there have been at least 25 validated MEG studies that indicate MEG can be used to determine the dominant hemisphere for language processing. The use of MEG neuroimaging techniques is needed to reliably predict altered language networks in patients and to provide identification of language eloquent cortices for localization and lateralization necessary for clinical care.

Visual Mapping With Magnetoencephalography: An Update on the Current State of Clinical Research and Practice With Considerations for Clinical Practice Guidelines.

Using visual evoked fields (VEFs) to differentiate healthy, normal brain function from dysfunctional cortex has been demonstrated to be both valid and reliable. Currently, VEFs are widely implemented to guide intracranial surgeries for epilepsy and brain tumors. There are several areas of possible future clinical use of VEFs, including early identification of disorders, such as multiple sclerosis, Parkinson's disease, stroke, and human immunodeficiency virus-associated neurocognitive disorders. These studies have suggested that VEFs could be used to study disease pathophysiology or as a biomarker for early identification of a disorder. The current clinical practice guidelines of the American Clinical Magnetoencephalography Society for VEFs are sufficient. At this time, VEFs should be used clinically to identify visual cortex and potentially tailor surgical resections.

High-gamma modulation language mapping with stereo-EEG: A novel analytic approach and diagnostic validation.

OBJECTIVE: A novel analytic approach for task-related high-gamma modulation (HGM) in stereo-electroencephalography (SEEG) was developed and evaluated for language mapping. METHODS: SEEG signals, acquired from drug-resistant epilepsy patients during a visual naming task, were analyzed to find clusters of 50-150 Hz power modulations in time-frequency domain. Classifier models to identify electrode contacts within the reference neuroanatomy and electrical stimulation mapping (ESM) speech/language sites were developed and validated. RESULTS: In 21 patients (9 females), aged 4.8-21.2 years, SEEG HGM model predicted electrode locations within Neurosynth language parcels with high diagnostic odds ratio (DOR 10.9, p < 0.0001), high specificity (0.85), and fair sensitivity (0.66). Another SEEG HGM model classified ESM speech/language sites with significant DOR (5.0, p < 0.0001), high specificity (0.74), but insufficient sensitivity. Time to largest power change reliably localized electrodes within Neurosynth language parcels, while, time to center-of-mass power change identified ESM sites. CONCLUSIONS: SEEG HGM mapping can accurately localize neuroanatomic and ESM language sites. SIGNIFICANCE: Predictive modelling incorporating time, frequency, and magnitude of power change is a useful methodology for task-related HGM, which offers insights into discrepancies between HGM language maps and neuroanatomy or ESM.

High Interrater Variability in Intraoperative Language Testing and Interpretation in Awake Brain Mapping Among Neurosurgeons or Neuropsychologists: An Emerging Need for Standardization.

OBJECTIVE: Brain mapping with direct electric stimulation is considered the gold standard for maximum safe resection of tumors affecting eloquent regions. However, no consensus exists in selection and interpretation of intraoperative testing for language and other cognitive domains. Our aim was to capture and statistically analyze variability in practices in intraoperative language testing among neurosurgeons and neuropsychologists in the United States, Europe, and the rest of the world. METHODS: An electronic questionnaire was developed by a multidisciplinary team at Queen Square, London, and distributed internationally through selected organized societies. The survey included 2 domains: terminology and common understanding of clinical deficits; and selection of intraoperative tests used per specific brain region. Participants were stratified by specialty, years of experience, and monthly caseload. Data were analyzed using Krippendorff α, Wilcoxon rank sum test, and Kruskal-Wallis analysis of variance. RESULTS: A total of 137 specialists participated. A low agreement was recorded for each of the 20 questions (Krippendorff α = -0.023 to 0.312). Further subgroup analysis revealed low interrater reliability independent of specialism (neurosurgeons, α = 0.013-0.318 compared with nonneurosurgeons, α = -0.021 to 0.398; P = 0.808) and years of experience (<1 years, α = -0.003 to 0.282; 2-5 years, α = 0.009-0.327; 6-10 years, α = 0.003-0.234; and >10 years, α = -0.003 to 0.372; P = 0.200). CONCLUSIONS: The current study documents high interrater variability, regardless of specialism and years of experience in the cohort of neurosurgeons and language specialists surveyed and may be applicable to a wider group of specialists, indicating the need to reduce interobserver, interinstitutional and interspecialty variability, reach consensus, and increase the validity, interpretation, and predictive power of intraoperative mapping.

Divergence between functional magnetic resonance imaging and clinical indicators of language dominance in preoperative language mapping.

Accurate determination of hemispheric language dominance prior to epilepsy surgery is critically important to minimize cognitive morbidity. Functional MRI (fMRI) is a noninvasive method that is highly concordant with other clinical indicators of language laterality, and is now commonly used to confirm language dominance. However, there is also a high frequency of divergence between fMRI findings and other clinical indices that complicate determination of dominance and surgical decision-making in individual patients. Despite this, divergent cases are rarely published or discussed. This article provides three illustrative examples to demonstrate common scenarios where fMRI may produce conflicting or otherwise difficult-to-interpret findings. We will also discuss potential reasons for divergence and propose a flow-chart to aid clinical decision making in such situations.

Invasive versus non-invasive mapping of the motor cortex.

Precise and comprehensive mapping of somatotopic representations in the motor cortex is clinically essential to achieve maximum resection of brain tumours whilst preserving motor function, especially since the current gold standard, that is, intraoperative direct cortical stimulation (DCS), holds limitations linked to the intraoperative setting such as time constraints or anatomical restrictions. Non-invasive techniques are increasingly relevant with regard to pre-operative risk-assessment. Here, we assessed the congruency of neuronavigated transcranial magnetic stimulation (nTMS) and functional magnetic resonance imaging (fMRI) with DCS. The motor representations of the hand, the foot and the tongue regions of 36 patients with intracranial tumours were mapped pre-operatively using nTMS and fMRI and by intraoperative DCS. Euclidean distances (ED) between hotspots/centres of gravity and (relative) overlaps of the maps were compared. We found significantly smaller EDs (11.4 ± 8.3 vs. 16.8 ± 7.0 mm) and better spatial overlaps (64 ± 38% vs. 37 ± 37%) between DCS and nTMS compared with DCS and fMRI. In contrast to DCS, fMRI and nTMS mappings were feasible for all regions and patients without complications. In summary, nTMS seems to be the more promising non-invasive motor cortex mapping technique to approximate the gold standard DCS results.

Use of the train-of-five bipolar technique to provide reliable, spatially accurate motor cortex identification in asleep patients.

OBJECTIVE: Intraoperative cortical and subcortical mapping techniques have become integral for achieving a maximal safe resection of tumors that are in or near regions of eloquent brain. The recent literature has demonstrated successful motor/language mapping with lower rates of stimulation-induced seizures when using monopolar high-frequency stimulation compared to traditional low-frequency bipolar stimulation mapping. However, monopolar stimulation carries with it disadvantages that include more radiant spread of electrical stimulation and a theoretically higher potential for tissue damage. The authors report on the successful use of bipolar stimulation with a high-frequency train-of-five (TOF) pulse physiology for motor mapping. METHODS: Between 2018 and 2019, 13 patients underwent motor mapping with phase-reversal and both low-frequency and high-frequency bipolar stimulation. A retrospective chart review was conducted to determine the success rate of motor mapping and to acquire intraoperative details. RESULTS: Thirteen patients underwent both high- and low-frequency bipolar motor mapping to aid in tumor resection. Of the lesions treated, 69% were gliomas, and the remainder were metastases. The motor cortex was identified at a significantly greater rate when using high-frequency TOF bipolar stimulation (n = 13) compared to the low-frequency bipolar stimulation (n = 4) (100% vs 31%, respectively; p = 0.0005). Intraoperative seizures and afterdischarges occurred only in the group of patients who underwent low-frequency bipolar stimulation, and none occurred in the TOF group (31% vs 0%, respectively; p = 0.09). CONCLUSIONS: Using a bipolar wand with high-frequency TOF stimulation, the authors achieved a significantly higher rate of successful motor mapping and a low rate of intraoperative seizure compared to traditional low-frequency bipolar stimulation. This preliminary study suggests that high-frequency TOF stimulation provides a reliable additional tool for motor cortex identification in asleep patients.

Accuracy analysis of fMRI and MEG activations determined by intraoperative mapping.

OBJECTIVE: By looking at how the accuracy of preoperative brain mapping methods vary according to differences in the distance from the activation clusters used for the analysis, the present study aimed to elucidate how preoperative functional neuroimaging may be used in such a way that maximizes the mapping accuracy. METHODS: The eloquent function of 19 patients with a brain tumor or cavernoma was mapped prior to resection with both functional MRI (fMRI) and magnetoencephalography (MEG). The mapping results were then validated using direct cortical stimulation mapping performed immediately after craniotomy and prior to resection. The subset of patients with equivalent MEG and fMRI tasks performed for motor (n = 14) and language (n = 12) were evaluated as both individual and combined predictions. Furthermore, the distance resulting in the maximum accuracy, as evaluated by the J statistic, was determined by plotting the sensitivities and specificities against a linearly increasing distance threshold. RESULTS: fMRI showed a maximum mapping accuracy at 5 mm for both motor and language mapping. MEG showed a maximum mapping accuracy at 40 mm for motor and 15 mm for language mapping. At the standard 10-mm distance used in the literature, MEG showed a greater specificity than fMRI for both motor and language mapping but a lower sensitivity for motor mapping. Combining MEG and fMRI showed a maximum accuracy at 15 mm and 5 mm-MEG and fMRI distances, respectively-for motor mapping and at a 10-mm distance for both MEG and fMRI for language mapping. For motor mapping, combining MEG and fMRI at the optimal distances resulted in a greater accuracy than the maximum accuracy of the individual predictions. CONCLUSIONS: This study demonstrates that the accuracy of language and motor mapping for both fMRI and MEG is heavily dependent on the distance threshold used in the analysis. Furthermore, combining MEG and fMRI showed the potential for increased motor mapping accuracy compared to when using the modalities separately.Clinical trial registration no.: NCT01535430 (clinicaltrials.gov).

Electrical stimulation mapping in children.

Electrical stimulation mapping is a longstanding practice that aids in identification and delineation of eloquent cortex. Initially used to expand our understanding of the typical human cortex, it now plays a significant role in mapping cortical function in individuals with atypical structural and functional tissue organization undergoing epilepsy surgery. This review discusses the unique challenges that arise in the functional testing of the immature cortex of a child and the parameters of stimulation that optimize accurate results in conventional open implantation and in stereo-electroencephalography. The prerequisite baseline evaluation and preparation recommended to increase the yield from pediatric stimulation mapping sessions is described, as are ideal approaches to the mapping of the sensory, motor, language, and visual cortices.

Real-time presurgical resting-state fMRI in patients with brain tumors: Quality control and comparison with task-fMRI and intraoperative mapping.

Resting-state functional magnetic resonance imaging (rsfMRI) is a promising task-free functional imaging approach, which may complement or replace task-based fMRI (tfMRI) in patients who have difficulties performing required tasks. However, rsfMRI is highly sensitive to head movement and physiological noise, and validation relative to tfMRI and intraoperative electrocortical mapping is still necessary. In this study, we investigate (a) the feasibility of real-time rsfMRI for presurgical mapping of eloquent networks with monitoring of data quality in patients with brain tumors and (b) rsfMRI localization of eloquent cortex compared with tfMRI and intraoperative electrocortical stimulation (ECS) in retrospective analysis. Five brain tumor patients were studied with rsfMRI and tfMRI on a clinical 3T scanner using MultiBand(8)-echo planar imaging (EPI) with repetition time: 400 ms. Moving-averaged sliding-window correlation analysis with regression of motion parameters and signals from white matter and cerebrospinal fluid was used to map sensorimotor and language resting-state networks. Data quality monitoring enabled rapid optimization of scan protocols, early identification of task noncompliance, and head movement-related false-positive connectivity to determine scan continuation or repetition. Sensorimotor and language resting-state networks were identifiable within 1 min of scan time. The Euclidean distance between ECS and rsfMRI connectivity and task-activation in motor cortex, Broca's, and Wernicke's areas was 5-10 mm, with the exception of discordant rsfMRI and ECS localization of Wernicke's area in one patient due to possible cortical reorganization and/or altered neurovascular coupling. This study demonstrates the potential of real-time high-speed rsfMRI for presurgical mapping of eloquent cortex with real-time data quality control, and clinically acceptable concordance of rsfMRI with tfMRI and ECS localization.

Automated fiber tract reconstruction for surgery planning: Extensive validation in language-related white matter tracts.

Diffusion MRI and tractography hold great potential for surgery planning, especially to preserve eloquent white matter during resections. However, fiber tract reconstruction requires an expert with detailed understanding of neuroanatomy. Several automated approaches have been proposed, using different strategies to reconstruct the white matter tracts in a supervised fashion. However, validation is often limited to comparison with manual delineation by overlap-based measures, which is limited in characterizing morphological and topological differences. In this work, we set up a fully automated pipeline based on anatomical criteria that does not require manual intervention, taking advantage of atlas-based criteria and advanced acquisition protocols available on clinical-grade MRI scanners. Then, we extensively validated it on epilepsy patients with specific focus on language-related bundles. The validation procedure encompasses different approaches, including simple overlap with manual segmentations from two experts, feasibility ratings from external multiple clinical raters and relation with task-based functional MRI. Overall, our results demonstrate good quantitative agreement between automated and manual segmentation, in most cases better performances of the proposed method in qualitative terms, and meaningful relationships with task-based fMRI. In addition, we observed significant differences between experts in terms of both manual segmentation and external ratings. These results offer important insights on how different levels of validation complement each other, supporting the idea that overlap-based measures, although quantitative, do not offer a full perspective on the similarities and differences between automated and manual methods.

Factors that modify the risk of intraoperative seizures triggered by electrical stimulation during supratentorial functional mapping.

OBJECTIVE: Intraoperative mapping via electrical stimulation is the gold standard technique for surgeries close to the eloquent cortex. However, it can trigger seizures which immediately impact patient's safety. We studied whether administration of antiepileptic drugs (AED) prior to and/or at the beginning of the surgery decreases the probability of triggering seizures, while adjusting for other risk factors. METHODS: 544 consecutive intraoperative mapping cases performed at a tertiary care center for epilepsy and brain tumor surgery were included in the study. Using a multivariate logistic regression analysis, we analyzed the independent impacts of AED loading at time of surgery, preoperative AED maintenance, history of seizures, type of stimulation paradigm, lobar location of stimulation, age, opioid administration and pathology on the probability of triggering seizures. RESULTS: Seizures were identified in 135 patients. Intravenous loading with AED decreased the odds of triggering seizures by 45% (OR = 0.55, p = 0.01), Penfield (versus multipulse train) stimulation and diffuse (versus well circumscribed) pathology increased it twice (OR = 1.97, p = 0.01) and 2.4 times (OR = 2.42, p = 0.003) respectively. No other factors had a significant impact. CONCLUSIONS: Seizures triggered during mapping occur frequently and are multifactorial. SIGNIFICANCE: Loading with AED independently reduces the risk of their occurrence.

Preoperative Resectability Estimates of Nonenhancing Glioma by Neurosurgeons and a Resection Probability Map.

BACKGROUND: Preoperative interpretation of resectability of diffuse nonenhancing glioma is primarily based on individual surgical expertise. OBJECTIVE: To compare the accuracy and precision between observed resections and preoperative estimates of neurosurgeons and a resection probability map (RPM). We hypothesize that the RPM estimates is as good as senior neurosurgeons. METHODS: A total of 234 consecutive patients were included from 2 centers, who had resective surgery with functional mapping between 2006 and 2012 for a supra-tentorial nonenhancing glioma. Extent of resection (EOR) and residual tumor volume (RTV) were segmented and an RPM was constructed in standard brain space. Three junior and three senior neurosurgeons estimated EOR and RTV, blinded for postoperative results. We determined the agreement between the estimates and calculated the diagnostic accuracy of the neurosurgeons and the RPM to predict the observed resections. RESULTS: Preoperative estimates of resection results by junior and senior neurosurgeons were significantly biased towards overestimation of EOR (4.2% and 11.2%) and underestimation of RTV (4.3 and 9.0 mL), whereas estimates of the RPM were unbiased (-2.6% and -.2 mL, respectively). The limits of agreement were wide for neurosurgeons and for the RPM. The RPM was significantly more accurate in identifying patients in whom an EOR >40% was observed than neurosurgeons. CONCLUSION: Neurosurgeons estimate preoperative resectability before surgery of a nonenhancing glioma rather accurate-with a small bias-and imprecise-with wide limits of agreement. An RPM provides unbiased resectability estimates, which can be useful for surgical decision-making, planning, and education.

High-resolution QSM for functional and structural depiction of subthalamic nuclei in DBS presurgical mapping.

OBJECTIVE: Faithful depiction of the subthalamic nucleus (STN) is critical for planning deep brain stimulation (DBS) surgery in patients with Parkinson's disease (PD). Quantitative susceptibility mapping (QSM) has been shown to be superior to traditional T2-weighted spin echo imaging (T2w). The aim of the study was to describe submillimeter QSM for preoperative imaging of the STN in planning of DBS. METHODS: Seven healthy volunteers were included in this study. T2w and QSM were obtained for all healthy volunteers, and images of different resolutions were reconstructed. Image quality and visibility of STN anatomical features were analyzed by a radiologist using a 5-point scale, and contrast properties of the STN and surrounding tissue were calculated. Additionally, data from 10 retrospectively and randomly selected PD patients who underwent 3-T MRI for DBS were analyzed for STN size and susceptibility gradient measurements. RESULTS: Higher contrast-to-noise ratio (CNR) values were observed in both high-resolution and low-resolution QSM images. Inter-resolution comparison demonstrated improvement in CNR for QSM, but not for T2w images. QSM provided higher inter-quadrant contrast ratios (CR) within the STN, and depicted a gradient in the distribution of susceptibility sources not visible in T2w images. CONCLUSIONS: For 3-T MRI, submillimeter QSM provides accurate delineation of the functional and anatomical STN features for DBS targeting.

A Guide for Cortical Electrical Stimulation Mapping.

Electrical stimulation mapping (ESM) of the brain remains a major procedure for guiding epilepsy and tumor surgeries. This article collates available experiences and data in ESM to develop a guide for conducting the procedure. There are many factors that influence the yield of ESM. The stimulation parameters offered in this article need to be adjusted within safe limits to address the factors. Each ESM procedure should be tailored to the patient's age and baseline mental or psychological capacity. Stimulation-induced seizures and EEG afterdischarges disrupt ESM procedure and render the interpretation of the results difficult. There are specific measures that can lessen the risk of seizures and afterdischarges during ESM. Electrical stimulation mapping procedure requires several tasks on the part of those conducting the procedure, such as operating the stimulator and the EEG recording equipment, administering behavioral or language tests and observing both patient and EEG responses to the stimulation. A team of experienced staff is necessary for individual assumption of each task. Knowledge of the spatial relationship between electrode contacts and underlying normal or abnormal brain structures is essential for interpreting ESM results. When testing for motor or sensory response, be aware of the distinction between responses at the primary motor area and responses at the supplementary sensorimotor area. The anatomy of supplementary sensorimotor area is more variable and functional than it is fixed and structural, although its general confines and somatotopic organization are known. In addition, negative motor responses to stimulation must be recognized to avoid misinterpretation of ESM results, especially in language mapping.

Improving surgical outcome for gliomas with intraoperative mapping.

INTRODUCTION: Radical glioma resection improves overall survival, both in low-grade and high-grade glial tumors. However, preservation of the quality of life is also crucial. Areas covered: Due to the diffuse feature of gliomas, which invade the central nervous system, and due to considerable variations of brain organization among patients, an individual cerebral mapping is mandatory to solve the classical dilemma between the oncological and functional issues. Because functional neuroimaging is not reliable enough, intraoperative electrical stimulation, especially in awake patients benefiting from a real-time cognitive monitoring, is the best way to increase the extent of resection while sparing eloquent neural networks. Expert commentary: Here, we propose a paradigmatic shift from image-guided resection to functional mapping-guided resection, based on the study of the dynamic distribution of delocalized cortico-subcortical circuits at the individual level, i.e., the investigation of brain connectomics and neuroplastic potential. This surgical philosophy results in an improvement of both oncological outcomes and quality of life. This highlights the need to reinforce the link between glioma surgery and cognitive neurosciences.

The clinical relevance of distortion correction in presurgical fMRI at 7T.

Presurgical planning with fMRI benefits from increased reliability and the possibility to reduce measurement time introduced by using ultra-high field. Echo-planar imaging suffers, however, from geometric distortions which scale with field strength and potentially give rise to clinically significant displacement of functional activation. We evaluate the effectiveness of a dynamic distortion correction (DDC) method based on unmodified single-echo EPI in the context of simulated presurgical planning fMRI at 7T and compare it with static distortion correction (SDC). The extent of distortion in EPI and activation shifts are investigated in a group of eleven patients with a range of neuropathologies who performed a motor task. The consequences of neglecting to correct images for susceptibility-induced distortions are assessed in a clinical context. It was possible to generate time series of EPI-based field maps which were free of artifacts in the eloquent brain areas relevant to presurgical fMRI, despite the presence of signal dropouts caused by pathologies and post-operative sites. Distortions of up to 5.1mm were observed in the primary motor cortex in raw EPI. These were accurately corrected with DDC and slightly less accurately with SDC. The dynamic nature of distortions in UHF clinical fMRI was demonstrated via investigation of temporal variation in voxel shift maps, confirming the potential inadequacy of SDC based on a single reference field map, particularly in the vicinity of pathologies or in the presence of motion. In two patients, the distortion correction was potentially clinically significant in that it might have affected the localization or interpretation of activation and could thereby have influenced the treatment plan. Distortion correction is shown to be effective and clinically relevant in presurgical planning at 7T.