Magnetoencephalography (MEG) and magnetic source imaging (MSI)

Rotary excitation of non-sinusoidal pulsed magnetic fields: Towards non-invasive direct detection of cardiac conduction

PURPOSE

There is a need for high resolution non-invasive imaging methods of physiologic magnetic fields. The purpose of this work is to develop a MRI detection approach for non-sinusoidal magnetic fields based on the rotary excitation (REX) mechanism which was previously successfully applied for the detection of oscillating magnetic fields in the sub-nT range.

METHODS

The new detection concept was examined by means of Bloch simulations, evaluating the interaction effect of spin-locked magnetization and low-frequency pulsed magnetic fields. The REX detection approach was validated under controlled conditions in phantom experiments at 3 T. Gaussian and sinc-shaped stimuli were investigated. In addition, the detection of artificial fields resembling a cardiac QRS complex, which is the most prominent peak visible on a magnetocardiogram, was tested.

RESULTS

Bloch simulations demonstrated that the REX method has a high sensitivity to pulsed fields in the resonance case, which is met when the spin-lock frequency coincides with a non-zero Fourier component of the stimulus field. In the experiments, we found that magnetic stimuli of different durations and waveforms can be distinguished by their characteristic REX response spectrum. The detected REX amplitude was proportional to the stimulus peak amplitude (R2 > 0.98) and the lowest field detection was 1 nT. Furthermore, the detection of QRS-like fields with varying QRS durations yielded significant results in a phantom setup (p < 0.001).

CONCLUSION

REX detection can be transferred to non-sinusoidal pulsed magnetic fields and could provide a non-invasive, quantitative tool for spatially resolved assessment of cardiac biomagnetism. Potential applications include the direct detection and characterization of cardiac conduction.

Detection of pathological high-frequency oscillations in refractory epilepsy patients undergoing simultaneous stereo-electroencephalography and magnetoencephalography

BACKGROUND

Stereo-electroencephalography (SEEG) and magnetoencephalography (MEG) have generally been used independently as part of the pre-surgical evaluation of drug-resistant epilepsy (DRE) patients. However, the possibility of simultaneously employing these recording techniques to determine whether MEG has the potential of offering the same information as SEEG less invasively, or whether it could offer a greater spatial indication of the epileptogenic zone (EZ) to aid surgical planning, has not been previously evaluated.

METHODS

Data from 24 paediatric and adult DRE patients, undergoing simultaneous SEEG and MEG as part of their pre-surgical evaluation, was analysed employing manual and automated high-frequency oscillations (HFOs) detection, and spectral and source localisation analyses.

RESULTS

Twelve patients (50%) were included in the analysis (4 males; mean age=25.08 years) and showed interictal SEEG and MEG HFOs. HFOs detection was concordant between the two recording modalities, but SEEG displayed higher ability of differentiating between deep and superficial epileptogenic sources. Automated HFO detector in MEG recordings was validated against the manual MEG detection method. Spectral analysis revealed that SEEG and MEG detect distinct epileptic events. The EZ was well correlated with the simultaneously recorded data in 50% patients, while 25% patients displayed poor correlation or discordance.

CONCLUSION

MEG recordings can detect HFOs, and simultaneous use of SEEG and MEG HFO identification facilitates EZ localisation during the presurgical planning stage for DRE patients. Further studies are necessary to validate these findings and support the translation of automated HFO detectors into routine clinical practice.

Investigation of neurophysiologic and functional connectivity changes following glioma resection using magnetoencephalography

Background

In patients with glioma, clinical manifestations of neural network disruption include behavioral changes, cognitive decline, and seizures. However, the extent of network recovery following surgery remains unclear. The aim of this study was to characterize the neurophysiologic and functional connectivity changes following glioma surgery using magnetoencephalography (MEG).

Methods

Ten patients with newly diagnosed intra-axial brain tumors undergoing surgical resection were enrolled in the study and completed at least two MEG recordings (pre-operative and immediate post-operative). An additional post-operative recording 6-8 weeks following surgery was obtained for six patients. Resting-state MEG recordings from 28 healthy controls were used for network-based comparisons. MEG data processing involved artifact suppression, high-pass filtering, and source localization. Functional connectivity between parcellated brain regions was estimated using coherence values from 116 virtual channels. Statistical analysis involved standard parametric tests.

Results

Distinct alterations in spectral power following tumor resection were observed, with at least three frequency bands affected across all study subjects. Tumor location-related changes were observed in specific frequency bands unique to each patient. Recovery of regional functional connectivity occurred following glioma resection, as determined by local coherence normalization. Changes in inter-regional functional connectivity were mapped across the brain, with comparable changes in low to mid gamma-associated functional connectivity noted in four patients.

Conclusion

Our findings provide a framework for future studies to examine other network changes in glioma patients. We demonstrate an intrinsic capacity for neural network regeneration in the post-operative setting. Further work should be aimed at correlating neurophysiologic changes with individual patients' clinical outcomes.

Changes in functional connectivity in newly diagnosed self-limited epilepsy with centrotemporal spikes and cognitive impairment: An MEG study

PURPOSE

Our purpose was to explore the relationship between cognitive impairment and neural network changes in patients newly diagnosed with self-limited epilepsy with centrotemporal spikes (SeLECTS).

METHODS

The Wechsler Intelligence Scale for Children, fourth edition was used to divide all SeLECTS patients into two groups: patients with full-scale intelligence quotient (FSIQ) below 80 that corresponded to cognitive impairment, and patients with FSIQ above 80 that corresponded to a normal cognitive function. The data on the resting state were recorded using magnetoencephalography. The properties of the networks were analyzed using graph theory (GT) analysis.

RESULTS

The functional connectivity (FC) of the frontal cortex in patients with FSIQ < 80 was reduced in the 12-30 Hz frequency band, and the FC of the posterior cingulate cortex was reduced in the 80-250 and 250-500 Hz frequency bands. The GT analysis showed that patients in the FSIQ < 80 group had higher strength in the 8-12 and 12-30 Hz frequency bands than those in the healthy control and FSIQ > 80 group. However, the path length was reduced in the 80-250 Hz band, and the clustering coefficient was reduced in the 12-30, 80-250, and 250-500 Hz frequency bands. Moreover, the receiver operator characteristic analysis showed that the clustering coefficient in the 12-30 and 80-250 Hz frequency bands, as well as the path length in the 80-250 Hz frequency band possessed a good discriminative ability in distinguishing the FSIQ > 80 group.

CONCLUSIONS

SeLECTS patients with cognitive impairment in the early stage of the disease developed disordered networks in cognitive-related brain regions. The clustering coefficient in the 12-30 and 80-250 Hz frequency bands as well as the path length in the 80-250 Hz frequency band might be good indicators to distinguish the cognitive impairment of SeLECTS patients at the early stage.

A Motor Imagery Signals Classification Method via the Difference of EEG Signals Between Left and Right Hemispheric Electrodes

Brain-computer interface (BCI) based on motor imagery (MI) can help patients with limb movement disorders in their normal life. In order to develop an efficient BCI system, it is necessary to decode high-accuracy motion intention by electroencephalogram (EEG) with low signal-to-noise ratio. In this article, a MI classification approach is proposed, combining the difference in EEG signals between the left and right hemispheric electrodes with a dual convolutional neural network (dual-CNN), which effectively improved the decoding performance of BCI. The positive and inverse problems of EEG were solved by the boundary element method (BEM) and weighted minimum norm estimation (WMNE), and then the scalp signals were mapped to the cortex layer. We created nine pairs of new electrodes on the cortex as the region of interest. The time series of the nine electrodes on the left and right hemispheric are respectively used as the input of the dual-CNN model to classify four MI tasks. The results show that this method has good results in both group-level subjects and individual subjects. On the Physionet database, the averaged accuracy on group-level can reach 96.36%, while the accuracies of four MI tasks reach 98.54, 95.02, 93.66, and 96.19%, respectively. As for the individual subject, the highest accuracy is 98.88%, and its four MI accuracies are 99.62, 99.68, 98.47, and 97.73%, respectively.

Development of nanotechnology-mediated precision radiotherapy for anti-metastasis and radioprotection

Radiotherapy (RT), including external beam RT and internal radiation therapy, uses high-energy ionizing radiation to kill tumor cells.

Clinical Validation of the Champagne Algorithm for Epilepsy Spike Localization

Magnetoencephalography (MEG) is increasingly used for presurgical planning in people with medically refractory focal epilepsy. Localization of interictal epileptiform activity, a surrogate for the seizure onset zone whose removal may prevent seizures, is challenging and depends on the use of multiple complementary techniques. Accurate and reliable localization of epileptiform activity from spontaneous MEG data has been an elusive goal. One approach toward this goal is to use a novel Bayesian inference algorithm-the Champagne algorithm with noise learning-which has shown tremendous success in source reconstruction, especially for focal brain sources. In this study, we localized sources of manually identified MEG spikes using the Champagne algorithm in a cohort of 16 patients with medically refractory epilepsy collected in two consecutive series. To evaluate the reliability of this approach, we compared the performance to equivalent current dipole (ECD) modeling, a conventional source localization technique that is commonly used in clinical practice. Results suggest that Champagne may be a robust, automated, alternative to manual parametric dipole fitting methods for localization of interictal MEG spikes, in addition to its previously described clinical and research applications.

A review of magnetoencephalography use in pediatric epilepsy: an update on best practice

Introduction: Magnetoencephalography (MEG) is a noninvasive technique that is used for presurgical evaluation of children with drug-resistant epilepsy (DRE).Areas covered: The contributions of MEG for localizing the epileptogenic zone are discussed, in particular in extra-temporal lobe epilepsy and focal cortical dysplasia, which are common in children, as well as in difficult to localize epilepsy such as operculo-insular epilepsy. Further, the authors review current evidence on MEG for mapping eloquent cortex, its performance, application in clinical practice, and potential challenges.Expert opinion: MEG could change the clinical management of children with DRE by directing placement of intracranial electrodes thereby enhancing their yield. With improved identification of a circumscribed epileptogenic zone, MEG could render more patients as suitable candidates for epilepsy surgery and increase utilization of surgery.

The relationship between epilepsy and cognitive function in benign childhood epilepsy with centrotemporal spikes

INTRODUCTION

This study was aimed to explore the relationship between neural network changes in newly diagnosed children with Benign Childhood Epilepsy with Centrotemporal Spikes (BECTS) and cognitive impairment.

METHODS

Children's cognition was evaluated using the Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV). Magnetoencephalographic (MEG) data of 18 healthy children and 22 BECTS patients were recorded in order to construct a functional connectivity (FC) network, which was quantified by graph theory (GT).

RESULTS

The mean age of the control group was 7.94 ± 1.89 years, and the mean age of BECTS patients was 8.14 ± 1.73 years. Our results show that the WISC-IV index scores in the BECTS group were significantly lower than those in the control group. Besides, the FC network pattern of BECTS patients changed significantly in the 12-30, 30-80, and 250-500 Hz frequency band. The local functional connections between posterior cingulate cortex (PCC) and frontal lobe varied significantly in 12-30, 80-250, and 250-500 Hz. Our GT analysis shows that the connection strength of BECTS patients increases significantly in the 12-30 Hz frequency band, the path length decreases significantly in the 12-30 Hz and 30-80 Hz frequency bands, with the clustering coefficient decreasing significantly in the 12-30 Hz, 30-80 Hz, and 250-500 Hz frequency bands. Correlation analysis showed that the full-scale IQ (FSIQ) was positively correlated with the 12-30 Hz clustering coefficient, verbal comprehension index (VCI) was positively correlated with the 250-500 Hz clustering coefficient, perceptual reasoning index (PRI) was positively correlated with the 12-30 Hz clustering coefficient, and perceptual reasoning index (PSI) was negatively correlated with the 12-30 Hz path length.

CONCLUSION

There is a trend of cognitive impairment in patients with early BECTS. This trend of cognitive impairment in early BECTS children may be related to the changes in the FC network pattern.

The relationship between neuromagnetic activity and cognitive function in benign childhood epilepsy with centrotemporal spikes

PURPOSE

Our aim was to explore the pathophysiological mechanism of cognitive function changes in early untreated children with benign childhood epilepsy with centrotemporal spikes (BECTS).

METHODS

Magnetoencephalography (MEG) was performed in 33 children with BECTS and 18 healthy children. Wechsler Intelligence Scale for Children, fourth edition (WISC-IV) was used to divide children with BECTS into two groups. Normal cognitive function was defined as a full-scale intelligence quotient (FSIQ) of >80, while decreased cognitive function was defined as a FSIQ of <80. Accumulated source imaging was used to evaluate the neuromagnetic source activity in multifrequency bands.

RESULTS

Of the 33 patients with early untreated BECTS, a total of 17 had a FSIQ of <80 and 16 had FSIQ of >80. The course of epilepsy and number of seizures in the FSIQ <80 group were higher than that in the FSIQ >80 group. Our MEG results showed that in the 4-8 Hz frequency band, both patient groups had inactivation of the posterior cingulate cortex (PCC) region compared with the healthy control group. In the 30-80 Hz frequency band, the FSIQ <80 group showed inactivation of the PCC region compared with both the healthy control group and the FSIQ >80 group. In the 80-250 Hz frequency band, the FSIQ <80 group had inactivated of the medial frontal cortex (MFC) region compared with the healthy control group. In the 30-80 Hz frequency band, the strength of neuromagnetic source in patients with BECTS with FSIQ <80 was higher than that in the FSIQ >80 group and the healthy control group.

CONCLUSIONS

The magnetic source inactivation of the MFC and PCC regions during the interictal time may be the reason for cognitive decline in early untreated children with BECTS. Children with BECTS with cognitive decline had a longer course of epilepsy and more seizures. The magnetic source localization in the 4-8 Hz frequency band may be a new imaging marker for the diagnosis of new BECTS.

Frequency-specific equivalence of brain activity on motor imagery during action observation and action execution

BACKGROUND

Human motor imagery (MI), action execution, and action observation (AO) are functionally considered as equivalent. MI during AO can extensively induce activation of motor-related brain network in the absence of overt movement. The magnetoencephalography (MEG) provides an important technology to reveal and reflect human brain information processing in multi-frequency bands. Utilizing a MEG system, we aimed to quantitatively investigate the frequency-specific equivalent characteristics in brain processing patterns between MI during AO and action execution in multi-frequency bands, including delta, theta, alpha, beta, gamma, and high-frequency oscillations.

METHODS

A total of 12 healthy subjects were studied with a whole-head MEG system during finger movement and MI during finger movement observation. We analyzed the brain activities in multi-frequency ranges of 1 Hz to 200 Hz.

RESULTS

Both MI during AO and action execution evoked the distinctive brain activities in low frequency ranges (i.e. delta, theta, and alpha). Significant differences were found in global spectral power between finger movement and MI during AO in delta and alpha oscillations. Compared with finger movement, delta (1-4 Hz) oscillation power in MI during AO were obviously decreased in left and right frontals and occipitals, and theta (4-8 Hz) and alpha (8-13 Hz) oscillation power were obviously increased in frontal, parietal and occipital.

CONCLUSION

MEG power evoked by finger movement and MI during AO is mainly concentrated in the energy distribution below 13 Hz. Furthermore, finger movement and MI during AO might share frequency-specific equivalence of brain neural activation dependent on different MEG frequency ranges.

Utility of magnetic source imaging in nonlesional focal epilepsy: a prospective study

OBJECTIVE

For patients with nonlesional refractory focal epilepsy (NLRFE), localization of the epileptogenic zone may be more arduous than for other types of epilepsy and frequently requires information from multiple noninvasive presurgical modalities and intracranial EEG (icEEG). In this prospective, blinded study, the authors assessed the clinical added value of magnetic source imaging (MSI) in the presurgical evaluation of patients with NLRFE.

METHODS

This study prospectively included 57 consecutive patients with NLRFE who were considered for epilepsy surgery. All patients underwent noninvasive presurgical evaluation and then MSI. To determine the surgical plan, discussion of the results of the presurgical evaluation was first undertaken while discussion participants were blinded to the MSI results. MSI results were then presented. MSI influence on the initial management plan was assessed.

RESULTS

MSI results influenced patient management in 32 patients. MSI results led to the following changes in surgical strategy in 14 patients (25%): allowing direct surgery in 6 patients through facilitating the detection of subtle cortical dysplasia in 4 patients and providing additional concordant diagnostic information to other presurgical workup in another 2 patients; rejection of surgery in 3 patients originally deemed surgical candidates; change of plan from direct surgery to icEEG in 2 patients; and allowing icEEG in 3 patients deemed not surgical candidates. MSI results led to changed electrode locations and contact numbers in another 18 patients. Epilepsy surgery was performed in 26 patients influenced by MSI results and good surgical outcome was achieved in 21 patients.

CONCLUSIONS

This prospective, blinded study showed that information provided by MSI allows more informed icEEG planning and surgical outcome in a significant percentage of patients with NLRFE and should be included in the presurgical workup in those patients.

Functional imaging

Functional imaging methodology has revolutionized our ability to understand brain-behavior relationships. In contrast with the static images obtained with standard imaging methods, functional images permit us to track brain activity as humans view stimuli, hear sounds, consider choices, and make decisions. The insights now possible because of this technology have not only provided new potential markers for disease but have also permitted questions of neural mechanism to be addressed in living humans. Because of the breadth and depth of research that directly or tangentially touches upon functional imaging, it is impossible to do justice to the various subfields, analysis streams, and methodological complexities in one chapter. Instead, this chapter will provide a brief overview of the underlying conceptual framework, basic analytic techniques, and details of the imaging methodologies available for the acquisition of functional imaging data.

Neuroimaging correlates of language network impairment and reorganization in temporal lobe epilepsy

Advanced, noninvasive imaging has revolutionized our understanding of language networks in the brain and is reshaping our approach to the presurgical evaluation of patients with epilepsy. Functional magnetic resonance imaging (fMRI) has had the greatest impact, unveiling the complexity of language organization and reorganization in patients with epilepsy both pre- and postoperatively, while volumetric MRI and diffusion tensor imaging have led to a greater appreciation of structural and microstructural correlates of language dysfunction in different epilepsy syndromes. In this article, we review recent literature describing how unimodal and multimodal imaging has advanced our knowledge of language networks and their plasticity in epilepsy, with a focus on the most frequently studied epilepsy syndrome in adults, temporal lobe epilepsy (TLE). We also describe how new analytic techniques (i.e., graph theory) are leading to a refined characterization of abnormal brain connectivity, and how subject-specific imaging profiles combined with clinical data may enhance the prediction of both seizure and language outcomes following surgical interventions.

Abnormality of visual neuromagnetic activation in female migraineurs without aura between attacks

OBJECTIVE

The present study aimed to preliminary explore the abnormal neuromagnetic activation in female migraine patients between attacks using magnetoencephalography (MEG) and pattern reversed visual evoked magnetic fields (PR-VEFs).

METHODS

A total of 17 female migraine subjects during the headache-free phase and 17 healthy controls (HC) were studied using a 275-channel magnetoencephalography (MEG) system. In this study, visual evoked magnetic fields (VEFs) were generated by a pattern-reversal check as the visual stimulus. The average of 100 VEFs was evolved by different half patterns were averaged and used to analyze waveform, spectrum, and source location within two frequency ranges (5-100 and 100-1000 Hz), respectively.

RESULTS

In migraine subjects, the latency of second peak of VEFs (VIIs) showed significant prolongations when compared with HC. On the sensor level, the cortical spectral power in migraine subjects was similar to that of HC in the 5-100 Hz range and was lower in the 1000-1000 Hz range. There was a decrement of source strength in the visual cortex in migraine patients when compared to HC in both the 5-100 and 100-1000 Hz frequency range. Moreover, there was a similar odds of activation in 5-100 and 100-1000 Hz frequency ranges in the area beyond the primary visual cortex between the two groups. In addition, no correlation was observed between clinical data (intensity of headache, headache-history duration, the frequency of headaches) and MEG results.

CONCLUSIONS

The findings presented in the current study, suggested that interictal cortical activation following a visual stimulus was low in female migraine patients. The low pre-activation was detected in the visual cortex using VEF and MEG in both low and high-frequency band. Our results add to the existing evidence that cortical interictal excitability change may be relative to the pain-module mechanism in migraine brains. Thus, our data improved the apprehension of the cortical disorder of migraine in the high-frequency domain.

The clinical impact of integration of magnetoencephalography in the presurgical workup for refractory nonlesional epilepsy

OBJECTIVE

For patients with nonlesional refractory focal epilepsy (NLRFE), localization of the epileptogenic zone is more arduous, and intracranial electroencephalography (EEG) (icEEG) is frequently required. Planning for icEEG is dependent on combined data from multiple noninvasive modalities. We report the negative impact of lack of integration of magnetoencephalography (MEG) in the presurgical workup in NLRFE.

METHODS

Observational MEG case series involving 31 consecutive patients with NLRFE in an academic epilepsy center. For various reasons, MEG data were not analyzed in a timely manner to be included in the decision-making process. The presumed impact of MEG was assessed retrospectively.

RESULTS

Magnetoencephalography would have changed the initial management in 21/31 (68%) had MEG results been available by reducing the number of intracranial electrodes, modifying their position, allowing for direct surgery, canceling the intracranial study, or providing enough evidence to justify one. Good surgical outcome was achieved in 11 out of 17 patients who proceeded to epilepsy surgery. Nine out of eleven had MEG clusters corresponding to the resection area, and MEG findings would have allowed for direct surgery (avoiding icEEG) in 2/11. Six patients had poor outcome including three patients where MEG would have significantly changed the outcome by modifying the resection margin. Magnetoencephalography provided superior information in 3 patients where inadequate coverage precluded accurate mapping of the epileptogenic zone.

CONCLUSION

In this single center retrospective study, MEG would have changed patient management, icEEG planning, and surgical outcome in a significant percentage of patients with NLRFE and should be considered in the presurgical workup in those patients.

Characterizing the effects of deep brain stimulation with magnetoencephalography: A review

BACKGROUND

Deep brain stimulation (DBS) is an important form of neuromodulation that is being applied to patients with motor, mood, or cognitive circuit disorders. Despite the efficacy and widespread use of DBS, the precise mechanisms by which it works remain unknown. Over the last decade, magnetoencephalography (MEG) has become an important functional neuroimaging technique used to study DBS.

OBJECTIVE

This review summarizes the literature related to the use of MEG to characterize the effects of DBS.

METHODS

Peer reviewed literature on DBS-MEG was obtained by searching the publicly accessible literature databases available on PubMed. The abstracts of all reports were scanned and publications which combined DBS-MEG in human subjects were selected for review.

RESULTS

A total of 32 publications met the selection criteria, and included studies which applied DBS for Parkinson's disease, dystonia, chronic pain, phantom limb pain, cluster headache, and epilepsy. DBS-MEG studies provided valuable insights into network connectivity, pathological coupling, and the modulatory effects of DBS.

CONCLUSIONS

As DBS-MEG research continues to develop, we can expect to gain a better understanding of diverse pathophysiological networks and their response to DBS. This knowledge will improve treatment efficacy, reduce side-effects, reveal optimal surgical targets, and advance the development of closed-loop neuromodulation.

A Comparative Study on the Detection of Covert Attention in Event-Related EEG and MEG Signals to Control a BCI

In brain-computer interface (BCI) applications the detection of neural processing as revealed by event-related potentials (ERPs) is a frequently used approach to regain communication for people unable to interact through any peripheral muscle control. However, the commonly used electroencephalography (EEG) provides signals of low signal-to-noise ratio, making the systems slow and inaccurate. As an alternative noninvasive recording technique, the magnetoencephalography (MEG) could provide more advantageous electrophysiological signals due to a higher number of sensors and the magnetic fields not being influenced by volume conduction. We investigated whether MEG provides higher accuracy in detecting event-related fields (ERFs) compared to detecting ERPs in simultaneously recorded EEG, both evoked by a covert attention task, and whether a combination of the modalities is advantageous. In our approach, a detection algorithm based on spatial filtering is used to identify ERP/ERF components in a data-driven manner. We found that MEG achieves higher decoding accuracy (DA) compared to EEG and that the combination of both further improves the performance significantly. However, MEG data showed poor performance in cross-subject classification, indicating that the algorithm's ability for transfer learning across subjects is better in EEG. Here we show that BCI control by covert attention is feasible with EEG and MEG using a data-driven spatial filter approach with a clear advantage of the MEG regarding DA but with a better transfer learning in EEG.

Using Magnetoencephalography to Study Patterns of Brain Magnetic Activity in Alzheimer’s Disease

The use of magnetoencephalography to study neurophysiologic abnormalities associated with Alzheimer’s disease is reviewed. The most consistent observation is that Alzheimer’s disease patients exhibit an increase in focal slow-wave activity that covaried with cognitive performance. It is still unclear whether generation of focal slow-wave activity precedes or is a consequence of Alzheimer’s disease-related neuropathology. Also reviewed is the use of magnetoencephalography to identify early functional changes preceding the diagnosis of dementia. Magnetoencephalography detected neurophysiologic abnormalities associated with cognitive deficits before the diagnosis of mild cognitive impairment. This is supported by evidence presented suggesting that some patients with subjective cognitive complaints, without evidence of dementia, show an increase in focal slow-wave generators. Further research is needed to determine whether the outstanding spatial and temporal resolution of the magnetoencephalography technique could complement other neuroimaging techniques in identifying neurophysiologic abnormalities preceding the diagnosis of Alzheimer’s disease and mild cognitive impairment.

Multi-frequency analysis of brain connectivity networks in migraineurs: a magnetoencephalography study

Background

Although alterations in resting-state neural network have been previously reported in migraine using functional MRI, whether this atypical neural network is frequency dependent remains unknown. The aim of this study was to investigate the alterations of the functional connectivity of neural network and their frequency specificity in migraineurs as compared with healthy controls by using magnetoencephalography (MEG) and concepts from graph theory.

Methods

Twenty-three episodic migraine patients with and without aura, during the interictal period, and 23 age- and gender-matched healthy controls at resting state with eye-closed were studied with MEG. Functional connectivity of neural network from low (0.1–1 Hz) to high (80–250 Hz) frequency ranges was analyzed with topographic patterns and quantified with graph theory.

Results

The topographic patterns of neural network showed that the migraineurs had significantly increased functional connectivity in the slow wave (0.1–1 Hz) band in the frontal area as compared with controls. Compared with the migraineurs without aura (MwoA), the migraineurs with aura (MwA) had significantly increased functional connectivity in the theta (4–8 Hz) band in the occipital area. Graph theory analysis revealed that the migraineurs had significantly increased connection strength in the slow wave (0.1–1 Hz) band, increased path length in the theta (4–8 Hz) and ripple (80–250 Hz) bands, and increased clustering coefficient in the slow wave (0.1–1 Hz) and theta (4–8 Hz) bands. The clinical characteristics had no significant correlation with interictal MEG parameters.

Conclusions

Results indicate that functional connectivity of neural network in migraine is significantly impaired in both low- and high-frequency ranges. The alteration of neural network may imply that migraine is associated with functional brain reorganization.

International Veterinary Epilepsy Task Force recommendations for a veterinary epilepsy-specific MRI protocol

Epilepsy is one of the most common chronic neurological diseases in veterinary practice. Magnetic resonance imaging (MRI) is regarded as an important diagnostic test to reach the diagnosis of idiopathic epilepsy. However, given that the diagnosis requires the exclusion of other differentials for seizures, the parameters for MRI examination should allow the detection of subtle lesions which may not be obvious with existing techniques. In addition, there are several differentials for idiopathic epilepsy in humans, for example some focal cortical dysplasias, which may only apparent with special sequences, imaging planes and/or particular techniques used in performing the MRI scan. As a result, there is a need to standardize MRI examination in veterinary patients with techniques that reliably diagnose subtle lesions, identify post-seizure changes, and which will allow for future identification of underlying causes of seizures not yet apparent in the veterinary literature.

There is a need for a standardized veterinary epilepsy-specific MRI protocol which will facilitate more detailed examination of areas susceptible to generating and perpetuating seizures, is cost efficient, simple to perform and can be adapted for both low and high field scanners. Standardisation of imaging will improve clinical communication and uniformity of case definition between research studies. A 6–7 sequence epilepsy-specific MRI protocol for veterinary patients is proposed and further advanced MR and functional imaging is reviewed.

Look back to leap forward: The emerging new role of magnetoencephalography (MEG) in nonlesional epilepsy

This review considers accumulating evidence for a new role of MEG/MSI in increasing the diagnostic yield of supposedly negative MRIs, and suggests changes in the use of MEG/MSI in presurgical epilepsy evaluations. Specific alterations in practice protocols for both the MEG practitioner (i.e. physician magnetoencephalographer) and MEG user (i.e. referring physician) are proposed that should further enhance the overall value of MEG/MSI. Although advances in MEG analysis methods will likely become increasingly assisted by computers, interpretive competency and prudent clinical judgment remain irreplaceable.

Resting state brain activity in patients with migraine: a magnetoencephalography study

Background

Recent advances in migraine research have shown that the cerebral cortex serves a primary role in the pathogenesis of migraine. Since aberrant brain activity in migraine can be noninvasively detected with magnetoencephalography (MEG), The object of this study was to investigate the resting state cortical activity differences between migraineurs and controls and its related clinical characteristics.

Methods

Twenty-two subjects with an acute migraine and twenty-two age- and gender-matched controls were studied using MEG. MEG recordings were recorded 120 seconds during the headache attack. Analyze MEG signals from low (1–4 Hz) to high (200–1000 Hz)-frequency ranges.

Results

In comparison with the controls, brain activity in migraine subjects was significantly different from that of the controls both in two frequency ranges (55–90 Hz, p < 0.001) and (90–200 Hz, p < 0.004). But the power value showed no significantly differences between control and migraines in all frequency ranges (p > 0.05). All the clinical characteristics had no significant correlation with aberrant brain activity.

Conclusions

The results demonstrated that migraine subjects in resting state had significantly aberrant ictal brain activity that can be measured with neuromagnetic imaging techniques. The findings may facilitate the development of new therapeutic strategies in migraine treatment via alterations in cortical excitability with TMS and other medications in the future.

Passive language mapping with magnetoencephalography in pediatric patients with epilepsy

OBJECT

Functional mapping is important for determining surgical candidacy and also in epilepsy surgery planning. However, in young children and uncooperative patients, language mapping has been particularly challenging despite the advances in performing noninvasive functional studies. In this study the authors review a series of children with epilepsy who underwent language mapping with magnetoencephalography (MEG) while sedated or sleeping, to determine receptive language localization for presurgical evaluation.

METHODS

The authors undertook a retrospective review of patients who underwent MEG between December 2007 and July 2009, and identified 15 individuals who underwent passive language testing as part of their presurgical evaluation because they were unable to participate in traditional language testing, such as Wada or functional MRI. Factors necessitating passive language testing included age and neurocognitive development.

RESULTS

Three of the 15 patients were deemed candidates for epilepsy surgery based on the results from standard preoperative testing, including video electroencephalography, MRI, and passive receptive language testing using MEG technology. The MEG studies were used successfully to localize language in all 3 patients, creating opportunities for seizure freedom through surgery that would not otherwise have been available. All 3 patients then underwent resective epilepsy surgery without experiencing postoperative language deficits.

CONCLUSIONS

This case series is the first to look at language mapping during sleep (passive language mapping) in which MEG was used and is the first to evaluate passive language testing in a patient population with intracranial pathological entities. This case series demonstrates that MEG can provide an alternative method for receptive language localization in patients with barriers to more traditional language testing, and in these 3 cases surgery was performed safely based on the results.

Localization of epileptic foci in Children with childhood absence epilepsy by magnetoencephalography combined with synthetic aperture magnetometry

This present study was aimed to investigate the localizable diagnostic value of magnetoencephalography (MEG) combined with synthetic aperture magnetometry (SAM) in childhood absence epilepsy (CAE). Thirteen CAE patients underwent MEG detection at resting state and after hyperventilation, and then the epileptic foci were located by SAM. In the thirteen CAE patients, epileptic foci were found in five cases (38.5%), and they were all located in the bilateral frontal lobe, suggesting that the frontal lobe in some CAE patients may serve as the epileptic foci. Our findings indicate that MEG combined with SAM could be of diagnostic value in localizing the epileptic foci in certain CAE patients.

rtMEG: a real-time software interface for magnetoencephalography

To date, the majority of studies using magnetoencephalography (MEG) rely on off-line analysis of the spatiotemporal properties of brain activity. Real-time MEG feedback could potentially benefit multiple areas of basic and clinical research: brain-machine interfaces, neurofeedback rehabilitation of stroke and spinal cord injury, and new adaptive paradigm designs, among others. We have developed a software interface to stream MEG signals in real time from the 306-channel Elekta Neuromag MEG system to an external workstation. The signals can be accessed with a minimal delay (≤45 ms) when data are sampled at 1000 Hz, which is sufficient for most real-time studies. We also show here that real-time source imaging is possible by demonstrating real-time monitoring and feedback of alpha-band power fluctuations over parieto-occipital and frontal areas. The interface is made available to the academic community as an open-source resource.

Mapping of the cortical spinal tracts using magnetoencephalography and diffusion tensor tractography in pediatric brain tumor patients

Prior to resection of a cerebral brain tumor, mapping of the functional and structural anatomy of the adjacent tissue is essential to reduce the risk of damage to descending and ascending pathways. We investigated the effectiveness of concurrent magnetoencephalography (MEG) and diffusion tensor imaging (DTI) tractography to delineate the motor cortex and associated corticospinal tract (CST) in a case series of children with brain tumors seen for pre-surgical evaluation. Using activation points generated from MEG to launch tractography, we delineated the CST of four patients and eight control subjects. Displacement of the CST was considerably larger in children with tumors located in the center of the hemisphere than in children whose tumors were more posteriorly located. Our findings suggest that the use of concurrent MEG and DTI may be an effective tool in the pre-surgical evaluation of eloquent cortex and associated white matter tracts in pediatric brain tumor patients.

Is the human left middle longitudinal fascicle essential for language? A brain electrostimulation study

Human brain pathways required for language processing are poorly known. A new white matter tract in humans, the middle longitudinal fascicle, has recently been anatomically determined by diffusion tensor imaging and suggested to be essential for language. Our aim is to determine the importance of the middle longitudinal fascicle for language processing. This study is based on 8 patients with glioma resection at least involving the superior temporal gyrus of the left dominant hemisphere. Language is systematically examined pre- and postoperatively at 3 months. Intraoperative electrostimulation is used to map cortical and subcortical structures as functional boundaries of the glioma resection, including those essential for language processing. The resections are extensive (on average 62 ml, ranging from 21 to 111 ml) and include a large part of the middle longitudinal fascicle in all patients. Intraoperatively, no interference with picture naming is observed by electrostimulation of the middle longitudinal fascicle, while in all patients the inferior fronto-occipital fascicle is identified by eliciting semantic paraphasia as functional boundary. Postoperatively, no new permanent language deficits are detected by systematic language examination. Therefore, we suggest that the middle longitudinal fascicle may participate but is not essential for language processing.

Structural and functional patterns in healthy aging, mild cognitive impairment, and Alzheimer disease

The aim of this study was to analyze the combined contribution of magnetic resonance imaging and magnetoencephalography (MEG) to the diagnosis of mild cognitive impairment (MCI) and AD. To whole-head MEG recordings were obtained from three diagnosis groups: Alzheimer disease (AD), MCI, and control. Magnetic resonance imaging volumetric data of global brain, temporal lobe, and hippocampal volumes, were also obtained. Results indicated that a reduction of volume in the hippocampal structure allowed the discrimination between AD and MCI patients as compared with controls. The percentage of correct classification was 91.3% when AD versus controls was compared, and 83.3% when we compared MCI versus control. MEG data showed that AD patients exhibit higher theta and delta activity than MCI and controls. Such higher activity was significant in parietal, temporal, and occipital areas. Left parietal theta classified controls versus MCIs with 78.3% rate of correct classification. Right occipital theta and the left parietal delta allowed the discrimination of controls versus ADs, with 81.8% rate of correct classification. Left parietal theta discriminated between ADs and MCIs with 56.6% rate of correct classification. In addition, the combination of both techniques significantly improved the rate of correct classification, thus indicating that a multidisciplinary perspective of techniques may improve the diagnostic capabilities.

Identification of abnormal neuromagnetic signatures in the motor cortex of adolescent migraine

OBJECTIVE

To investigate the functional abnormalities of the motor cortices in children with migraine using magnetoencephalography (MEG) and a finger-tapping task.

BACKGROUND

Cortical hyperexcitability has been reported in adults with migraine using MEG. Many children with migraine report difficulty with motor functioning. There is no report on motor-evoked magnetic activation in children with migraine using MEG and the latest signal processing methods.

METHODS

Ten children with migraine (all female, 9 right-handed and 1 left-handed, aged 13-17 years) and 10 age- and gender-matched healthy children were studied with a 275-channel MEG system. After hearing a unilateral, randomly presented sound cue (500 Hz, 30 milliseconds square tone), each subject immediately performed a brisk index finger tapping with either the right or the left index finger. The auditory stimuli consisted of 200 trials of square tone, 100 trials per ear, randomly distributed. The latency and amplitude of neuromagnetic responses were analyzed with averaged waveforms. Neuromagnetic sources were estimated using synthetic aperture magnetometry (SAM). SAM images were normalized for each participant for group comparison.

RESULTS

In comparison with healthy children, children with migraine had prolonged latency of motor-evoked magnetic response in the right hemispheres during left finger movement (62.33 +/- 34.55 milliseconds vs 34.9 +/- 17.29 milliseconds, P < .05). In addition, children with migraine had stronger activation in the motor cortex during right finger movement (8097.46 +/- 5168.99 vs 4697.54 +/- 3194.74, P < .05).

CONCLUSIONS

The results suggest that there are neurophysiological changes in the motor cortices of children with migraine that can be measured with neuromagnetic imaging techniques. The findings expand the ability to study the cerebral mechanisms of migraine using MEG and may facilitate the development of new therapeutic strategies in migraine treatment via alterations in cortical excitability.

Lateralizing language with magnetic source imaging: validation based on the Wada test

PURPOSE

Magnetoencephalography (MEG)/magnetic source imaging (MSI) is a noninvasive functional neuroimaging procedure used to localize language-specific regions in the brain. The Wada test, or intracarotid amobarbital procedure (IAP), is the gold standard in determining speech/language lateralization for presurgical planning, although it is invasive and associated with morbidity. The purpose of this study is to provide further validation on the use of MSI for presurgical language lateralization by comparing results against the IAP.

METHODS

The sample consisted of 35 patients with epilepsy and/or brain tumor undergoing presurgical evaluation at the Minnesota Epilepsy Group. All patients received both an IAP and MSI to determine hemispheric language dominance. For MSI, a 148-channel MEG system was used to record activation of language-specific cortex by an auditory word-recognition task.

RESULTS

The MSI and IAP were concordant in determining language in the hemisphere to be treated in 86% of the cases with sensitivity and specificity values of 80% and 100%, respectively.

CONCLUSIONS

The results from this study are consistent with prior research findings comparing functional neuroimaging procedures to the IAP in determining language lateralization in presurgical patients. The current study provides an important replication and support for Papanicolaou et al.'s findings in 2004 using a consecutive clinical sample from a different institution. An unusually high rate of atypical IAP language cases in this sample and differences between the two procedures are believed to explain the noted discrepancies. MSI is a viable noninvasive alternative to the IAP in the presurgical determination of language lateralization.

Functional Neuroimaging of Language Using Magnetoencephalography

Magnetoencephalography (MEG) is a novel functional brain mapping technique capable of non-invasively measuring neurophysiological activity based on direct measures of the magnetic flux at the head surface associated with the synchronized electrical activity of neuronal populations. Among the most actively sought applications of MEG has been localization of language-specific cortex. This is in part due to its practical application for pre-surgical evaluation of patients with epilepsy or brain tumors. Until recently, comprehensive language mapping during surgical planning has relied on the application of invasive diagnostic methods, namely the Wada procedure and direct electrocortical stimulation mapping, often considered as the "gold standard" techniques for identifying language-specific cortex. In this review, we evaluate the utility of MEG as a tool for functional mapping of language in both clinical and normal populations. In particular, we provide a general description of MEG, with emphasis on facets of the technique related to language mapping. Additionally, we discuss the application of appropriate MEG language-mapping protocols developed to reliably generate spatiotemporal profiles of language activity, and address the validity of the technique against the "gold standards" of the Wada and electrocortical mapping procedures.

Presurgical Localization of Primary Motor Cortex in Pediatric Patients with Brain Lesions by the Use of Spatially Filtered Magnetoencephalography

Objective:

The objective of this study was to confirm the efficacy of spatially filtered magnetoencephalography for the preoperative localization of primary motor cortex in pediatric patients with focal lesions in the region of the sensorimotor cortex.

Methods:

We recorded movement-related magnetoencephalographic activity in 10 pediatric patients (age range, 7–18 years; mean age, 12.5 years) undergoing presurgical evaluation for focal brain lesion resection. Participants made transient movements of the right and left index finger in response to a visual cue. The premovement motor field component in the averaged brain response was localized with a newly developed beamformer spatial filter algorithm. Cortical mapping of motor cortex intraoperatively was conducted in 5 of the 10 patients.

Results:

The motor field time-locked to electromyography onset was successfully localized to cortical areas corresponding to the hand region primary motor cortex in 95% of cases (9 of 10 from nonlesional hemisphere; 10 of 10 from lesional hemisphere). Intraoperative electrocortical stimulation activated the expected muscles at motor field coregistered cortical source locations in all cases tested (n = 5). Using these methods, we also found that displacement of the sensorimotor cortex by space-occupying tumors did not interfere with the localization of motor cortex.

Conclusion:

We conclude that noninvasive localization of the primary motor cortex can be reliably performed by using spatially filtered magnetoencephalography techniques, which provide a robust and accurate measurement of motor cortical function for the purpose of surgical guidance.

Magnetoencephalography for clinical pediatrics: the effect of head positioning on measurement of somatosensory-evoked fields

OBJECTIVE

At present, whole-head MEG systems are designed to accommodate adult heads, thereby introducing a technical issue unique to pediatric MEG. It is known that magnetic field strength decreases as a function of 1/distance(2). For pediatric patients, we questioned whether re-positioning the head to minimize the distance between the expected source location and the MEG sensor array would significantly improve source measurement.

METHODS

Somatosensory-evoked fields (SEFs) were recorded in 17 children (mean=4.96 years) with their head placed centrally in the MEG, and then re-positioned laterally to reduce the distance between the cortical source and sensors. Equivalent current dipole (ECD) source models were evaluated for changes in residual variance (RV), signal-to-noise ratio (SNR), moment (strength), and location.

RESULTS

Re-positioning the head closer to the sensors resulted in a significant shift in the mediolateral dipole coordinate location, accompanied by a significant increase in the SNR, decrease in the dipole RV, and a reduction in size of ECD confidence volumes.

CONCLUSIONS

We conclude that for clinical pediatric measurement of the SEF, repositioning of the head to minimize the distance between the expected SEF source location and the sensor array will significantly improve SEF source measurement and concomitant ECD source modeling.

SIGNIFICANCE

These issues are relevant to all pediatric MEG settings involving healthy or clinical populations and underscores the need for future development of a MEG helmet specifically designed for pediatric populations.

Somatosensory-evoked fields on magnetoencephalography for epilepsy infants younger than 4 years with total intravenous anesthesia

OBJECTIVE

Patients must remain immobile for magnetoencephalography (MEG) and MRI recordings to allow precise localization of brain function for pre-surgical functional mapping. In young children with epilepsy, this is accomplished with recordings during sleep or with anesthesia. This paper demonstrates that MEG can detect, characterize and localize somatosensory-evoked fields (SEF) in infants younger than 4 years of age with or without total intravenous anesthesia (TIVA).

METHODS

We investigated the latency, amplitude, residual error (RE) and location of the N20m of the SEF in 26 infants (mean age=2.6 years). Seventeen patients underwent TIVA and 9 patients were tested while asleep, without TIVA.

RESULTS

MEG detected 44 reliable SEFs (77%) in 52 median nerve stimulations. We found 27 reliable SEFs (79%) with TIVA and 13 reliable SEFs (72%) without TIVA. TIVA effects included longer latencies (p<0.001) and lower RE (p<0.05) compared to those without TIVA. Older patients and larger head circumferences also showed significantly shorter latencies (p<0.01).

CONCLUSIONS

TIVA resulted in reliable SEFs with lower RE and longer latencies.

SIGNIFICANCE

MEG can detect reliable SEFs in infants younger than 4 years old. When infants require TIVA for MEG and MRI acquisition, SEFs can still be reliably observed.

Fast oscillations associated with interictal spikes localize the epileptogenic zone in patients with partial epilepsy

Although interictal epileptic spikes are defined as fast transient activity, the spatial distribution of spike-related high-frequency power changes is unknown. In this study, we localized the sources of spike-locked power increases in the beta and gamma band with magnetoencephalography and an adaptive spatial filtering technique and tested the usefulness of these reconstructions for determining the epileptogenic zone in a population of 27 consecutive presurgical patients with medication refractory partial epilepsies. The reliability of this approach was compared to the performance of conventional MEG techniques such as equivalent current dipole (ECD) models. In patients with good surgical outcome after a mean follow-up time of 16 months (Engel class I or II), the surgically resected area was identified with an accuracy of 85% by sources of spike-locked beta/gamma activity, which compared favorably with the accuracy of 69% found for ECD models of single spikes. In patients with a total of more than 50 spikes in their recordings, the accuracies increased to 100% vs. 88%, respectively. Imaging of spike-locked beta/gamma power changes therefore seems to be a reliable and fast alternative to conventional MEG techniques for localizing epileptogenic tissue, in particular, if more than 50 interictal spikes can be recorded.

Event-related beamforming: a robust method for presurgical functional mapping using MEG

OBJECTIVE

We describe the application of a new spatial filtering technique--event-related beamforming (ERB)--for presurgical functional mapping of primary sensory areas using MEG. This method provides an alternative to equivalent current dipole (ECD) modeling that potentially eliminates problems of intracranial magnetic artifacts due to movement of ferromagnetic materials (e.g., orthodontic braces) or eye movements.

METHODS

We compared localization results for ERB and ECD localization of primary somatosensory (M20) and auditory (M100) evoked responses in 12 healthy control subjects and four subjects with metallic dental implants. Data were recorded with a 151-channel CTF MEG system using standard presurgical mapping protocols.

RESULTS

We found a high level of agreement between the two methods in control subjects (overall localization difference was 5.9+/-2.2 mm for M20 and 10.4+/-5.6 mm for M100). Subjects with dental implants showed severely distorted evoked responses that could not be analyzed using ECD, whereas the ERB method localized sources to expected anatomical locations.

CONCLUSIONS

MEG functional mapping may be carried out without removal of orthodontic or other metallic implants using event-related beamformer analysis.

SIGNIFICANCE

Spatial filtering methods can overcome some of the limitations associated with MEG expanding its applicability, particularly in pediatric clinical environments.

Combined EEG and MEG analysis of early somatosensory evoked activity in children and adolescents with focal epilepsies

OBJECTIVE

The study aimed to evaluate differences between EEG and MEG analysis of early somatosensory evoked activity in patients with focal epilepsies in localizing eloquent areas of the somatosensory cortex.

METHODS

Twenty-five patients (12 male, 13 female; age 4-25 years, mean 11.7 years) were included. Syndromes were classified as symptomatic in 17, idiopathic in 2 and cryptogenic in 6 cases. 10 patients presented with malformations of cortical development (MCD). 122 channel MEG and simultaneous 33-channel EEG were recorded during tactile stimulation of the thumb (sampling rate 769 Hz, band-pass 0.3-260 Hz). Forty-four hemispheres were analyzed. Hemispheres were classified as type I: normal (15), II: central structural lesion (16), III: no lesion, but central epileptic discharges (ED, 8), IV: lesion or ED outside the central region (5). Analysis of both sides including one normal and one type II or III hemisphere was possible in 15 patients. Recordings were repeated in 18 hemispheres overall. Averaged data segments were filtered (10-250 Hz) and analyzed off-line with BESA. Latencies and amplitudes of N20 and P30 were analyzed. A regional source was fitted for localizing S1 by MRI co-registration. Orientation of EEG N20 was calculated from a single dipole model.

RESULTS

EEG and MEG lead to comparable good results in all normal hemispheres. Only EEG detected N20/P30 in 3 hemispheres of types II/III while MEG showed no signal. N20 dipoles had a more radial orientation in these cases. MEG added information in one hemisphere, when EEG source analysis of a clear N20 was not possible because of a low signal-to-noise ratio. Overall N20 dipoles had a more radial orientation in type II when compared to type I hemispheres (p=0.01). Further N20/P30 parameters (amplitudes, latencies, localization related to central sulcus) showed no significant differences between affected and normal hemispheres. Early somatosensory evoked activity was preserved within the visible lesion in 5 of the 10 patients with MCD.

CONCLUSIONS

MEG should be combined with EEG when analyzing tactile evoked activities in hemispheres with a central structural lesion or ED focus.

SIGNIFICANCE

At time, MEG analysis is frequently applied without simultaneous EEG. Our results clearly show that EEG may be superior under specific circumstances and combination is necessary when analyzing activity from anatomically altered cortex.

Mechanisms of anesthetic actions and the brain

The neural mechanisms behind anesthetic-induced behavioral changes such as loss of consciousness, amnesia, and analgesia, are insufficiently understood, though general anesthesia has been of tremendous importance for the development of medicine. In this review, I summarize what is currently known about general anesthetic actions at different organizational levels and discuss current and future research, using systems neuroscience approaches such as functional neuroimaging and quantitative electrophysiology to understand anesthesia actions at the integrated brain level.

Hemispheric language dominance in magnetoencephalography: sensitivity, specificity, and data reduction techniques

Understanding the areas involved in language functions not only enables investigators to understand neuroanatomical structures, but may be a promising technique in the presurgical evaluation of epilepsy. The predictive power of various data reduction techniques was tested on language data obtained by magnetoencephalography (MEG) of 16 patients and 12 control subjects. Words were presented aurally in two phases: the study phase and the recognition phase. Subjects were asked to remember words from the study phase and indicate if they remembered those words during the recognition phase. Single equivalent-current dipoles were calculated to determine laterality indices and the neuroanatomical correlates of language function. For all patients, results indicated a concordance, sensitivity, and specificity of 0.75. After consideration of IQ scores and exclusion from the analysis of those patients with scores below the average range, the results indicated a concordance of 0.90, sensitivity of 0.86, and specificity of 1.00. These findings are consistent with previous MEG investigations of language function in comparison with the Wada technique and support the use of MEG language mapping in most patients with an IQ within or above the average range.

Neuroimaging of Focal Cortical Dysplasia

Focal cortical dysplasia (FCD) is a common cause of pharmacoresistant epilepsy that is amenable to surgical resective treatment. The identification of structural FCD by magnetic resonance imaging (MRI) can contribute to the detection of the epileptogenic zone and improve the outcome of epilepsy surgery. MR epilepsy protocols that include specific T1 and T2 weighted, and fluid-attenuated inversion recovery (FLAIR) sequences give complementary information about the characteristic imaging features of FCD; focal cortical thickening, blurring of the gray-white junction, high FLAIR signal, and gyral anatomical abnormalities. Novel imaging techniques such as magnetic resonance spectroscopy (MRS), magnetization transfer imaging (MTI), and diffusion tensor imaging (DTI) can improve the sensitivity of MR to localize the anatomical lesion. Functional/metabolic techniques such as positron emission tomography (PET), ictal subtraction single photon emission computed tomography (SPECT), functional MRI (fMRI), and magnetic source imaging (MSI) have the potential to visualize the metabolic, vascular, and epileptogenic properties of the FCD lesion, respectively. Identification of eloquent areas of cortex, to assist in the surgical resection plan, can be obtained non-invasively through the use of fMRI and MSI. Although a significant number of FCD lesions remain unidentified using current neuroimaging techniques, future advances should result in the identification of an increasing number of these cortical malformations.

Evolving and experimental technologies in medical imaging

Medical images are created by detecting radiation probes transmitted through or emitted or scattered by the body. The radiation, modulated through interactions with tissues, yields patterns that provide anatomic and/or physiologic information. X-rays, gamma rays, radiofrequency signals, and ultrasound waves are the standard probes, but others like visible and infrared light, microwaves, terahertz rays, and intrinsic and applied electric and magnetic fields are being explored. Some of the younger technologies, such as molecular imaging, may enhance existing imaging modalities; however, they also, in combination with nanotechnology, biotechnology, bioinformatics, and new forms of computational hardware and software, may well lead to novel approaches to clinical imaging. This review provides a brief overview of the current state of image-based diagnostic medicine and offers comments on the directions in which some of its subfields may be heading.

Volumetric localization of epileptic activities in tuberous sclerosis using synthetic aperture magnetometry

BACKGROUND

Magnetoencephalography (MEG) is a novel noninvasive technique for localizing epileptic zones. Tuberous sclerosis complex (TSC) is often associated with medically refractory epilepsy with multiple epileptic zones. Surgical treatment of TSC requires accurate localization of epileptogenic tubers.

OBJECTIVE

The objective of this study was to introduce a new MEG technique, synthetic aperture magnetometry (SAM), to volumetrically localize irritable zones and clarify the correlations between SAM, dipole modeling and anatomical tubers.

MATERIALS AND METHODS

Eight pediatric patients with TSC confirmed by clinical and neuroimaging findings were retrospectively studied. MEG data were recorded using a whole-cortex CTF OMEGA system. Sleep deprivation was employed to provoke epileptiform activity. Irritable zones were localized using both dipole modeling and SAM.

RESULTS

MRI detected 42 tubers in the eight patients. Dipole modeling localized 28 irritable zones, and 19 out of the 28 zones were near tubers (19/42, 45%). SAM found 51 irritable zones, and 31 out of the 51 zones were near tubers (31/42, 74%). Among the 51 irritable zones determined by SAM, thirty-five zones were in 1-35 Hz, nine zones were in 35-60 Hz, and seven zones were in 60-120 Hz.

CONCLUSIONS

The new method, SAM, yielded very plausible equivalent sources for patients who showed anatomical tubers on MRI. Compared to conventional dipole modeling, SAM appeared to offer increased detection of irritable zones and beneficial volumetric and frequency descriptions.

Retrospective review of MEG visual evoked hemifield responses prior to resection of temporo-parieto-occipital lesions

Visual evoked cortical magnetic field (VEF) waveforms were recorded from both hemifields in 21 patients with temporo-parieto-occipital mass lesions to identify preserved visual pathways. Fifteen patients had visual symptoms pre-operatively. Magnetoencephalographic (MEG) VEF responses were detected, using single equivalent current dipole (ECD), in 17/21 patients studied. Displaced or abnormal responses were seen in 15 patients with disruption of pathway in one patient. Three of 21 patients had alterations in the surgical approach or the planned resection based on the MEG findings. The surgical outcome for these three patients suggests that the MEG study may have played a useful role in pre-surgical planning.

Neuroimaging of Metastatic Brain Disease

This review discusses imaging techniques for the diagnosis, treatment, and monitoring of brain metastases. It assesses the various modalities on the basis of their respective advantages and limitations. Recent advances in imaging technologies provide evaluation that is more accurate for tumor localization, morphology, physiology, and biology. When used in combination, these technologies provide clinicians with a powerful diagnostic and prognostic tool for managing metastatic brain disease.