Investigation of perfusion in osseous vessels in close vicinity to piezo-electric bone cutting.

Cutting bones by piezosurgery leads to failure of perfusion at the site of the osteotomy, the cause of which cannot be identified immediately. Among other things the formation of vascular thrombi by the transmission of oscillations from the piezoelectric unit to the bone may be responsible. We used three output levels of oscillation that were predefined by the system. The outer cortical bone of the calvaria of rats (n=24) was removed horizontally and the intraosseous vessels exposed at the surface of the osteotomy. The blood flow was then examined repeatedly using intravital fluorescence microscopy. To calculate the transmission of oscillations to the bone, the spatial oscillation frequency of each calvarium and the contact pressure during removal of bone in vitro (n=18) were also examined. After removal of the bone there was constant blood flow at all three levels of oscillation output. In no case did an individual vessel seem to be occluded. The excitation oscillation of the bone was established at 2000 Hz in all spatial directions, irrespective of the predefined oscillation output. The application of piezosurgery does not cause the formation of vascular thrombi in the bone. This probably results from the oscillation damping properties of bone.

Image-guided removal of supratentorial cavernomas in critical brain areas: application of neuronavigation and intraoperative magnetic resonance imaging.

In a retrospective study the postoperative results of 26 patients operated on for supratentorial cavernous hemangiomas either deep-seated or near eloquent brain areas are summarized. An exact surgical approach to these lesions is essential to prevent neurological deterioration. Three different navigation systems were used and compared according to their clinical applicability. Complete removal of the lesion was obtained in all patients of this series. In six cases (23 %) functional data from magnetoencephalography or functional magnetic resonance imaging were integrated into the navigational setup. In 14 cases (54 %) intraoperative magnetic resonance imaging was performed. The follow-up time was 3 - 26 months (mean: 10 months). In the postoperative course one patient (3.8 %) developed a hemiparesis, another one developed quadrantopia. Nineteen patients presented with preoperative seizure history, 16 of these (84 %) had no further or rare seizures after surgery. The better results in seizure control were achieved in those patients with shorter duration of seizure history before surgery. The study indicates that the application of neuronavigation allows surgery on supratentorial cavernous hemangiomas in critical brain areas with low morbidity. The intraoperative visualization of eloquent cortex areas by integration of functional data allows a fast identification and exemption of eloquent brain areas, preventing neurological deterioration. Furthermore, the intraoperative MR resection control ensures a complete resection and illustrates the minimal invasive approach.

Spontaneous, slow and fast magnetoencephalographic activity in patients with schizophrenia.

A 2* 37 channel biomagnetic system (Magnes II) was used to record spontaneous magnetic activity for the frequency ranges 2-6 Hz and 12.5-30 Hz in 30 patients with schizophrenia (23 men and 17 women) and 30 healthy volunteers in both hemispheres during a resting condition. The dipole localization was calculated by the dipole density plot (DDP) method, which is a spatial averaging in order to decrease the influence of the nonfocal activity. The quantified DDP results were superimposed to T2-weighted MR-images of each patient's head as isocontour lines. To superimpose the MEG results to 3-D MRI data, the scanned head data set was fitted to the reconstructed MRI head shape using a surface fit programme developed by our department. The absolute dipole values were correlated with the psychopathological findings and the cumulative neuroleptic dosage for each patient. The group of patients with schizophrenia differed overall from the healthy subjects in the elevation of absolute dipole values measured in both hemispheres. For the region of slow dipole activity (2-6 Hz), a high correlation was found between the intensity of dipole concentration and productive psychotic symptoms (PANSS, P1-P7). Dipole localization (for both frequency ranges) showed a concentration effect (DCE) in the temporoparietal region in patients with schizophrenia.

[Use of magnetoencephalography and functional neuronavigation in planning and surgery of brain tumors]. / Der Nutzen von Magnetoenzephalographie und funktioneller Neuronavigation bei der Planung und Operation von Hirntumoren.

The role of magnetoencephalography (MEG) in neurology has been established for basic research, epilepsy, and functional brain mapping. The presurgical localization of functionally important brain areas has evolved as an important application of MEG. Both neurologists and neurosurgeons can use this method for decision-making and planning of nonsurgical or surgical treatment in brain tumors. The integration of functional brain mapping data into neuronavigation systems may help to minimize postoperative morbidity. This is especially important in low-grade gliomas, in which a potential benefit of surgery is only achieved when the tumor has been resected completely, whereas neurological deterioration means a substantial loss of quality of life during the survival time. This report addresses the utility of MEG combined with neuronavigation in the treatment of brain tumors adjacent to eloquent brain areas.

Correlation of sensorimotor activation with functional magnetic resonance imaging and magnetoencephalography in presurgical functional imaging: a spatial analysis.

In this study we investigated the spatial heterotopy of MEG and fMRI localizations after sensory and motor stimulation tasks. Both methods are frequently used to study the topology of the primary and secondary motor cortex, as well as a tool for presurgical brain mapping. fMRI was performed with a 1.5T MR system, using echo-planar imaging with a motor and a sensory task. Somatosensory and motor evoked fields were recorded with a biomagnetometer. fMRI activation was determined with a cross-correlation analysis. MEG source localization was performed with a single equivalent current dipole model and a current density localization approach. Distances between MEG and fMRI activation sites were measured within the same anatomical 3-D-MR image set. The central region could be identified by MEG and fMRI in 33 of 34 cases. However, MEG and fMRI localization results showed significantly different activation sites for the motor and sensory task with a distance of 10 and 15 mm, respectively. This reflects the different neurophysiological mechanisms: direct neuronal current flow (MEG) and secondary changes in cerebral blood flow and oxygenation level of activated versus non activated brain structures (fMRI). The result of our study has clinical implications when MEG and fMRI localizations are used for pre- and intraoperative brain mapping. Although both modalities are useful for the estimation of the motor cortex, a single modality may err in the exact topographical labeling of the motor cortex. In some unclear cases a combination of both methods should be used in order to avoid neurological deficits.

New approach to localize speech relevant brain areas and hemispheric dominance using spatially filtered magnetoencephalography.

We used a current localization by spatial filtering-technique to determine primary language areas with magnetoencephalography (MEG) using a silent reading and a silent naming task. In all cases we could localize the sensory speech area (Wernicke) in the posterior part of the left superior temporal gyrus (Brodmann area 22) and the motor speech area (Broca) in the left inferior frontal gyrus (Brodmann area 44). Left hemispheric speech dominance was determined in all cases by a laterality index comparing the current source strength of the activated left side speech areas to their right side homologous. In 12 cases we found early Wernicke and later Broca activation corresponding to the Wernicke-Geschwind model. In three cases, however, we also found early Broca activation indicating that speech-related brain areas need not necessarily be activated sequentially but can also be activated simultaneously. Magnetoencephalography can be a potent tool for functional mapping of speech-related brain areas in individuals, investigating the time-course of brain activation, and identifying the speech dominant hemisphere. This may have implications for presurgical planning in epilepsy and brain tumor patients.

A combined study of tumor-related brain lesions using MEG and proton MR spectroscopic imaging.

The purpose of this study is to localize, in cases of brain tumors, pathological magnetic brain activities and to analyze metabolic alterations in functionally abnormal lesions using magnetoencephalography (MEG) and proton magnetic resonance spectroscopic imaging (1H MRSI). The study focused on 10 healthy volunteers and seven patients with common brain tumors, namely astrocytic tumor and meningioma. In spontaneous MEG, the pathological brain activities (slow, fast waves and spikes) were localized using a single equivalent dipole model. After the results of MEG and 1H MRSI were superimposed onto the corresponding MR images, the signal intensities of spectroscopically visible metabolites were analyzed in the regions where the dipoles of the pathological activities were concentrated. Increased slow wave activity was observed in four cases and fast wave or spike activity was significantly increased in one case. These pathological activities were localized in surrounding regions of the bulk of tumors, where mild reduction of N-acetyl aspartate (NAA) and slight accumulation of lactate (Lac) consistently existed. Preserved cortical areas, which are indicated by residual NAA, might be able to generate pathological magnetic activities under lactic acidosis. Such areas could be understood as a border zone between normal and seriously damaged brain tissue by tumors or associated brain edema. This combined technique with the different modalities gives insight into functional as well as metabolic aspects of pathological brain conditions.

Intraoperative magnetic resonance imaging combined with neuronavigation: a new concept.

OBJECTIVE: Intraoperative image data may be used not only to evaluate the extent of a tumor resection but also to update neuronavigation, compensating for brain shift. To date, however, intraoperative magnetic resonance imaging (MRI) can be combined only with navigation microscopes that are separated from the magnetic field, thus requiring time-consuming intraoperative patient transport. To help solve this problem, we investigated whether a new navigation microscope can be used within the fringe field of the MRI scanner. METHODS: The navigation microscope was placed at the 5-G line of a 0.2 MRI device. Patients were positioned lying down directly on the table of the scanner, with their heads placed approximately 1.5 m from the center of the magnet, fixed in an MRI-compatible ceramic head holder. Standard operating instruments were used. For intraoperative imaging, we slid the table into the center of the magnet in less than 30 seconds. RESULTS: By use of this setup, we operated on 22 patients. In all patients, anatomic neuronavigation could be used in combination with intraoperative MRI. In addition, in 12 patients, functional data from magnetoencephalographic or functional MRI studies were integrated, resulting in functional neuronavigation. We did not encounter adverse effects of the low magnetic field during navigation. Moreover, intraoperative imaging was not disturbed by the navigation microscope and vice versa. CONCLUSION: Functional neuronavigation and intraoperative MRI can be used essentially simultaneously without the need for lengthy intraoperative patient transport. The combination of intraoperative imaging with functional neuronavigation offers the opportunity for more radical resections and fewer complications.

Time course of focal slow wave activity in transient ischemic attacks and transient global amnesia as measured by magnetoencephalography.

In this longitudinal study multichannel MEG was used to localize and to quantify focal pathological spontaneous neuromagnetic activity in six patients with transient ischemic attacks (TIA) and two patients with transient global amnesia (TGA). Slow (2-6 Hz) and beta (14-30 Hz) activity were monitored up to 10 weeks. Results were compared with normative data, and changes over time were statistically analyzed. MEG detected pathological activity that persisted clinical symptoms. Focal slow activity originating from sensorimotor (TIA) and mesiotemporal (TGA) cortices exceeded normal values up to 14 times during the first hours after the attack and recovered to normal within 11 days. Focal beta activity was not useful to monitor the time course of TIA or TGA.

Magnetoencephalography in extratemporal epilepsy.

Epilepsy surgery candidates with extratemporal foci represent a particular diagnostic and therapeutic challenge, because of anatomic and functional features of the pertaining areas. In the last decade, novel developments in the field of electrophysiological techniques have offered new approaches to detailed localization of specific epileptic discharges as well as eloquent regions. Magnetoencephalography, in combination with neuroimaging data and simultaneously recorded EEG, yields promising results to clarify centers of epileptic activity and their relationship to structural abnormalites and functionally significant areas. Examples are given to illustrate the range of applications of this method as a contribution to routine presurgical evaluation.

The electrical and magnetical cerebral responses evoked by electrical stimulation of the esophagus and the location of their cerebral sources.

OBJECTIVES: After electrical stimulation of the esophagus cerebral responses are recordable, their cortical source is under discussion. Brain mapping using electroencephalography recordings demonstrated partially controversial results. Sources of evoked responses can be localized more easily using magnetoencephalography than electroencephalography. METHODS: We examined 22 volunteers by recording electrical somatosensory potentials after electrical stimulation of the esophagus. In 9 of these 22 subjects additional recording of magnetic fields was performed and the sources of the evoked magnetic fields were computed. RESULTS: The evoked potentials after electrical stimulation of the esophagus had a similar latency as the previously published data. The source localization done by magnetoencephalography suggest that first a region of the postcentral gyrus is activated which is temporo-lateral to the primary somatosensory cortex of the pharynx. This region is suggested to be the primary somatosensory region of the esophagus. This source was followed by a source in the parietal operculum thought being part of the secondary somatosensory cortex. Simultaneously the insular cortex was activated pointing to a parallel neuronal pathway to the central autonomic nervous system. CONCLUSION: After electrical stimulation of the esophagus somatosensory cortical areas of the temporal postcentral gyrus and the operculum are activated. In parallel activation of the insular cortex as part of the central autonomic network was found.

Functional neuronavigation with magnetoencephalography: outcome in 50 patients with lesions around the motor cortex.

OBJECT: The authors conducted a study to evaluate the clinical outcome in 50 patients with lesions around the motor cortex who underwent surgery in which functional neuronavigation was performed. METHODS: The sensorimotor cortex was identified in all patients with the use of magnetoencephalography (MEG). The MEG-source localizations were superimposed onto a three-dimensional magnetic resonance image and the image data set was implemented into a neuronavigation system. Based on this setup, the surgeon chose the best surgical strategy. During surgery, the pre- and postcentral gyri were identified by neuronavigation and, in addition, the central sulcus was localized using intraoperative recording of somatosensory evoked potentials. In all cases MEG localizations of the sensory or motor cortex were correct. In 30% of the patients preoperative paresis improved, in 66% no additional deficits occurred, and in only 4% (two patients) deterioration of neurological function occurred. In one of these patients the deterioration was not related to the procedure. CONCLUSIONS: The method of incorporating functional data into neuronavigation systems is a promising tool that can be used in more radical surgery to lessen morbidity around eloquent brain areas.

Integration of functional magnetic resonance imaging supported by magnetoencephalography in functional neuronavigation

OBJECTIVE: In this study, the intraoperative visualization of functional data provided by functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) leading to functional neuronavigation is demonstrated in surgery around the motor strip. METHODS: In seven patients with lesions adjacent to the central region, fMRI was performed with a 1.5-Tesla magnetic resonance system, using axial echo-planar imaging with a motor and a sensory task. Somatosensory and motor evoked fields were recorded with a biomagnetometer. fMRI and MEG were matched to an anatomic three-dimensional magnetic resonance image set by a contour fit. Then this three-dimensional image data set was transferred to the navigation microscope and displayed in the eyepieces of the microscope during surgery. Additionally, intraoperative recording of somatosensory evoked potentials was performed for verification of the central sulcus. RESULTS: In all cases, the projection of fMRI and MEG data into the operating viewing field allowed easy identification of the central region, which was confirmed by phase reversal of somatosensory evoked potentials in each case. fMRI and MEG measurements yielded corresponding results in each patient. CONCLUSION: Functional neuronavigation with integration of fMRI and MEG allows the fast identification of eloquent brain areas. The widespread availability of fMRI will result in a broad availability of functional neuronavigation, which will, in turn, contribute to the successful surgery of lesions in eloquent brain areas with lower morbidity.

Focal slow and beta brain activity in patients with multiple sclerosis revealed by magnetoencephalography.

In multiple sclerosis (MS) inflammatory infiltrations cause white matter lesions. Magnetoencephalography (MEG) offers the opportunity to localize abnormal electric activity of neurons with a high spatio-temporal resolution. In this study, we investigated patients with MS in order to find if abnormal cortical activity is associated with (subcortical) MS lesions using simultaneous bilateral recording of biomagnetic activity. Eight patients suffering from definite laboratory-supported MS with mainly somatosensory deficits and multiple bihemispheric plaques revealed by MRI were included in the study. To obtain normative data, 8 healthy volunteers were investigated following the same measuring protocol. Spontaneous magnetic brain activity was recorded using a 2x37-channel biomagnetic system (BTI, USA). Offline analysis included digital filtering (to separately investigate slow and beta wave activity), a Principle Component Analysis and the Dipole Density Plot. Localization results were inserted into MR images using our contour fit procedure. The dipole distribution in the brain was quantified and compared between the groups by statistical analysis. In all MS patients, the maximum of focal abnormal activity was localized in cortical areas adjacent to the fiber lesions. In the healthy subjects, no focal abnormal brain activity could be found. However, the standardized maximum concentrations of dipoles were significantly higher in the MS patients than in the healthy control group both in the slow and in the beta wave analysis. These results let assume that subcortical lesions can occur together with abnormal cortical neuronal activity. The results are discussed in respect to their impact on the interpretation of the analysis of spontaneous magnetic brain activity.

A combined study of tumor-related brain lesions by using magnetoencephalography and 1H magnetic resonance spectroscopic imaging. Technical note.

The purpose of this study was to localize pathological magnetic brain activities and to analyze metabolic alterations in functionally abnormal lesions by using magnetoencephalography (MEG) and (1)H magnetic resonance (MR) spectroscopy in patients with brain tumors. The authors studied 10 healthy volunteers and seven patients who harbored common brain tumors, namely astrocytic tumors and meningioma. In spontaneous MEG the pathological brain activities (slow waves, fast waves, and spikes) were localized using a single equivalent dipole model. After the results of MEG and (1)H MR spectroscopy were superimposed onto the corresponding MR images, the signal intensities of spectroscopically visible metabolites were analyzed in the regions in which the dipoles of the pathological activities were concentrated. Increased slow-wave activity was observed in four cases, and fast-wave or spike activity was significantly increased in one case each, respectively. These pathological activities were localized at almost the same cortical areas adjacent to the bulk of tumors, where mild reduction of N-acetyl aspartate (NAA) and slight accumulation of lactate consistently existed. Preserved and metabolically active cortical areas, which are indicated by residual NAA, might be able to generate pathological magnetic activities under lactic acidosis. Such an area could be understood as a border zone between normal brain tissue and brain tissue that has been seriously damaged by tumors or associated edema, which should be intensively treated. This combination of imaging techniques gives insight into functional as well as metabolic aspects of pathological brain conditions.

Functional neuronavigation with magnetoencephalography: outcome in 50 patients with lesions around the motor cortex.

The authors conducted a study to evaluate the clinical outcome in 50 patients with lesions around the motor cortex who underwent surgery in which functional neuronavigation was performed. The sensorimotor cortex was identified in all patients with the use of magnetoencephalography (MEG). The MEG-source localizations were superimposed onto a three-dimensional magnetic resonance image, and the image data set was then implemented into a neuronavigation system. Based on this setup, the surgeon chose the best surgical strategy. During surgery, the pre- and postcentral gyrus were identified by neuronavigation, and in addition, the central sulcus was localized using intraoperative recording of somatosensory evoked potentials. In all cases MEG localizations of the sensory or motor cortex were correct. In 30% of the patients preoperative paresis improved, in 66% no additional deficits occurred, and in only 4% (two patients) deterioration of neurological function occurred. In one of these patients the deterioration was not related to the method. The method of incorporating functional data into neuronavigation systems is a promising tool that can be used in more radical surgery to cause less morbidity around eloquent brain areas.

Responses to silent Kanji reading of the native Japanese and German in task subtraction magnetoencephalography.

The neuromagnetic activities evoked by semantic processing were localized by magnetoencephalography (MEG). We observed distinct time courses of the activities in native speaking Japanese subjects (Japanese speaker) and German subjects (German speaker) during silent reading of Japanese letters; Kanji and meaningless figures made by deforming the Arabian letters. There were significant differences in amplitude of the activities between Kanji and meaningless figure stimuli. The responses with meaningless figure stimuli were subtracted from those with Kanji stimuli to demonstrate the semantic responses. Earlier responses peaked at about 273.3+/-50. 8 and 245.0+/-23.8 ms (mean+/-S.D.) and were mainly located in the right fusiform gyrus (FuG) in the Japanese and German speakers, respectively. All the Japanese speakers constantly showed additional later responses in the left superior temporal gyrus (STG) and the supramarginal gyrus (SmG) at approximately 616.1+/-105.5 ms, whereas no further activity was observed in the German speakers who did not know the meaning of each Kanji. Because the later responses in the STG and SmG in the Japanese speakers were only observed in their dominant hemisphere, we believe the source of these responses to be part of the neural basis of Kanji semantic processing. The task subtraction MEG analysis could be a powerful method to discriminate distinct responses and visualize the neural networks involved in semantic processing.

Motor, somatosensory and auditory cortex localization by fMRI and MEG.

Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were performed in six subjects during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using identical stimulation paradigms. Both functional imaging modalities localized brain activity in adjacent areas of anatomically correct cortex. The mean distances measured between fMRI activity and the corresponding MEG dipoles were 10.1 mm (motor), 10.7 mm (somatosensory), 13.5 mm (auditory right hemisphere) and 14.3 mm (auditory left hemisphere). The distances found may reflect the correlation between electrophysiological and hemodynamic responses due to the different underlying substrates of neurophysiology measured by fMRI and MEG: BOLD contrast vs neuronal biomagnetic activity.

Localization analysis of neuronal activities in benign rolandic epilepsy using magnetoencephalography.

Benign epilepsy of childhood with rolandic spikes (BECRS) is an electroclinical syndrome characterized by partial sensorimotor seizures with centrotemporal spikes. We report a detailed localization analysis of spontaneous magnetic brain activities in seven BECRS patients using magnetoencephalography (MEG). All patients had BECRS diagnosis with typical seizures and electroencephalographic findings and five patients had minor psychomotor deficits. MEG was recorded over both parieto-temporal regions using a 2x37-channel biomagnetic system. The collected data were digitally bandpass-filtered (2-6, 14-30, or 1-70 Hz) to analyze slow- and fast-wave magnetic activities and rolandic spikes. Slow-wave activity was increased in four hemispheres of three patients. Increased fast-wave activity was found in all five patients with minor neuropsychological deficits. The presence of increased fast-wave magnetic brain activity appeared to cause functional anomalies in the higher brain function processes. In the spike analysis, the dipoles of rolandic spikes which constantly manifested anterior positivity in direction were concentrated in the superior rolandic region in four cases and the inferior rolandic region in three cases. The localizations of increased slow- and fast-wave activities were identical with those of the spikes. The seizure profiles were frequently characterized by the spike locations. Source localizations of the focal brain activities and rolandic spikes by MEG will contribute to the different diagnosis and pathophysiological elucidation of BECRS.