脑磁图研究进展与临床应用

脑磁图具有全头多磁道传感系统和综合信息处理能力,与MRI信息整合形成脑功能解剖图像,成为研究脑功能和诊断神经系统疾病重要的医疗设备。本文主要综述近十年来脑磁图的研究及应用的进展情况。     

脑磁图在脑肿瘤外科中的临床应用

随着脑磁图(MEG)在临床应用的不断发展,其在神经疾病的诊治中发挥着越来越大的作用。除了在顽固性癫痫患者术前致痫灶定位方面具有一定的作用外,它在脑肿瘤的外科治疗中也起到一定的指导作用,尤其是当肿瘤位于脑功能区时。脑肿瘤外科术前通过应用MEG定位大脑皮层的感觉、运动和语言功能区(PSFM)的方法明显优于fMRI和术中电刺激,同时它还可以指导脑肿瘤微创外科手术,并有助于手术方式的选择及判断预后。将PSFM结果与导航系统相结合,可以避免在手术中损伤重要的功能区,提高了患者术后的生活质量。对于那些脑肿瘤伴有癫痫的患者,术前除了可以进行功能区定位外,它还可以明确肿瘤与癫痫的关系,从而指导外科手术治疗。     

脑磁图的研究与临床应用

用超导技术制作的超感度磁力计来测定脑磁场的变化已开始用于临床。脑磁图是一种无侵袭性测定脑电活动的方法,可以用于(1)确定癫痫患者的脑内病灶;(2)检查体感诱发电位;揭示控制机体各部位功能活动的中枢在大脑皮质上的分布。本文简要介绍检测脑磁图的原理和临床用途,以及研究现状。     

南京脑科医院脑磁图中心脑磁图简介

脑磁图(MEG)是一种通过测量脑磁场信号.进行癫痫病灶和脑功能区定位的新技术.对人体无侵袭、无损害.具有极高的敏感性和时间.空间分辨率。MEG可对脑磁信号及其发生源进行精确测定和定位.并通过影像融合技术叠加于MRI影像上.即磁源性影像(MS)实现了大脑功能和解剖的统一。我院引进的是加拿大VSM公司最新型CTF-275信道全头型脑磁图系统。     

南京脑科医院脑磁图中心脑磁图简介

<正>脑磁图(MEG)是一种通过测量脑磁场信号,进行癫痫病灶和脑功能区定位的新技术,对人体无侵袭、无损害,具有极高的敏感性和时间,空间分辨率。MEG可对脑磁信号及其发生源进行精确测定和定位,并通过影像融合技术叠加于MRI影像上,即磁源性影像(MSI),实现了大脑功能和解剖的统一。我院引进的是加拿大VSM公司最新型CTF-275信道全头型脑磁图系统,是目前华东地区唯一一台脑磁图,开展包括癫痫病灶的定位,脑功能区定位(视觉、听觉、运动、体感、语言认知)等项目,作为评估     

南京脑科医院脑磁图中心 脑磁图简介

脑磁图（MEG）是一种通过测量脑磁场信号，进行癫痫病灶和脑功能区定位的新技术，对人体无侵袭、无损害，具有极高的敏感性和时间．空间分辨率。MEG可对脑磁信号及其发生源进行精确测定和定位．并通过影像融合技术叠加于MRI影像上，即磁源性影像（MSI），实现了大脑功能和解剖的统一。我院引进的是加拿大VSM公司最新型CTF-275信道全头型脑磁图系统，是目前华东地区唯一一台脑磁图，开展包括癫痫病灶的定位，脑功能区定位（视觉、听觉、运动、体感、语言认知）等项目，作为评估和指导癫痫手术的重要手段；神经外科手术前功能区的定位，     

南京脑科医院脑磁图中心脑磁图简介

<正>脑磁图(MEG)是一种通过测量脑磁场信号,进行癫痫病灶和脑功能区定位的新技术,对人体无侵袭、无损害,具有极高的敏感性和时间,空间分辨率。MEG可对脑磁信号及其发生源进行精确测定和定位,并通过影像融合技术叠加于MRI影像上,即磁源性影像(MSI),实现了大脑功能和解剖的统一。我院引进的是加拿大VSM公司最新型CTF-275信道全头型脑磁图系统,是目前     

南京脑科医院脑磁图中心脑磁图简介

正脑磁图(MEG)是一种通过测量脑磁场信号,进行癫痫病灶和脑功能区定位的新技术,对人体无侵袭、无损害,具有极高的敏感性和时间,空间分辨率。MEG可对脑磁信号及其发生源进行精确测定和定位,并通过影像融合技术叠加于MRI影像上,即磁源性影像(MSI),实现了大脑功能和解剖的统一。我院引进的是加拿大VSM公司最新型CTF-275信道全头型脑磁图系统,是目前华东地区唯一一台脑磁图,开展包括癫痫病灶的定位,脑功能区定位(视觉、听觉、运动、体感、语言认知)等项目,作为评估     

南京脑科医院脑磁图中心脑磁图简介

正脑磁图(MEG)是一种通过测量脑磁场信号,进行癫痫病灶和脑功能区定位的新技术,对人体无侵袭,无损害,具有极高的敏感性和时间,空间分辨率。MEG可对脑磁信号及其发生源进行精确测定和定位,并通过影像融合技术叠加于MRI影像上,即磁源性影像(MSI),实现了大脑功能和解剖的统一。我院引进的是加拿大VSM公司最新型CTF-275信道全头型脑磁图系统,是目前华东地区唯一一台脑磁图,开展包括癫痫病灶的定位,脑功能区     

南京脑科医院脑磁图中心脑磁图简介

<正>脑磁图(MEG)是一种通过测量脑磁场信号,进行癫痫病灶和脑功能区定位的新技术,对人体无侵袭、无损害,具有极高的敏感性和时间,空间分辨率。MEG可对脑磁信号及其发生源进行精确测定和定位,并通过影像融合技术叠加于MRI影像上,即磁源性影像(MSI),实现了大脑功能和解剖的统一。我院引进的是加拿大VSM公司最新型CTF-275信道全头型脑磁图系统,是目前     

Comparison of the magnetoencephalogram and electroencephalogram.

The spatial response of the magnetoencephalogram (MEG) to sources in the brain's cortex is compared with that of the electroencephalogram (EEG). This is done using computer modeling of the head which is approximated by 4 concentric spherical regions that represent the brain and surrounding bone and tissue. Lead fields are calculated at points on the cortex for unipolar, bipolar and quadrupolar MEG and EEG measurements. Since lead fields are patterns of the sensitivity of these measurements to a source at various locations and orientations, they provide a convenient means for comparison. It is found that a unipolar MEG has a very different lead field than a unipolar EEG. Hence, this type of MEG detects sources at different locations and orientations than this EEG. Although bipolar MEG and EEG lead fields are found to have similar patterns, the MEG lead field is narrower than that of the EEG and hence 'sees' a smaller area on the cortex than the EEG. This is because the potentials measured by the EEG are 'smeared' by the low-conductivity skull; the magnetic fields measured by the MEG are not smeared. Quadrupolar MEG and EEG lead fields are found to be about the same. The responses of bipolar MEGs and EEGs to distributed sources, which are composed of aligned and randomly oriented dipoles, are compared. It is found that for both types of sources, the MEG 'sees' an area on the cortex which is approximately 0.3 times that for the EEG. Hence, the MEG appears to be useful for detecting a more restricted group of sources than the EEG.     

Demonstration of useful differences between magnetoencephalogram and electroencephalogram

For a dipole source, theory predicts 3 useful differences between the MEG and EEG spatial patterns over the head. These are seen when a comparison is made between theoretical MEG and EEG maps, due to the dipole in a spherical model of the head. If true, these differences would allow the MEG to better localize or differentiate neural sources in some ways than does the EEG. A first experimental test of the differences is made here. A comparison is made between MEG and EEG maps due to a neural source which appears to behave as a dipole (N20 of the somatic evoked response). The same 3 differences are seen, therefore the predicted differences are confirmed experimentally. The first 2 differences, due only to the tangential component of the dipole, are that the MEG pattern is rotated by 90 degrees from the EEG pattern and is one-third tighter. The first allows the MEG to localize a tangential dipole better in a preferred direction, across the dipole (while the EEG does so along the dipole); the second allows the MEG to localize somewhat better in its preferred direction than the EEG does in its preferred direction. The third difference is due only to the radial component of the dipole; while the MEG receives no contribution from this component, the EEG pattern is asymmetrical and is heavily weighted by it. This allows the MEG to reveal tangential sources which are obscured by the radial sources in the EEG. For sources which cannot be approximated by a dipole, the MEG-EEG differences will depend on the particular case; however, the spherical model can now be used with more confidence to predict differences in these cases.     

Frontal gamma-band activity in magnetoencephalogram during auditory oddball processing

Previous studies have demonstrated induced gamma-band activity (GBA) over posterior temporo-parietal and inferior frontal cortex during auditory spatial vs pattern mismatch processing, respectively. Here we investigated magnetoencephalographic oscillatory responses during an active auditory pattern oddball task. Fourteen subjects were instructed to detect pairs of deviating animal vocalizations in a sequence of standard sounds. The comparison of targets with standards revealed differences in oscillatory activity >80 Hz 200-300 ms after stimulus onset. GBA was increased over left inferior frontal cortex, replicating previous results of putative auditory ventral stream activation during passive pattern deviance processing. Additional GBA enhancements over superior frontal cortex were specific to active target detection. They probably reflected executive networks involved in memory maintenance and decision making.     

Alpha entrainment in human electroencephalogram and magnetoencephalogram recordings

Visual stimulation by repetitive flashes of light can lead to an entrainment of the alpha rhythm in electroencephalogram recordings (also called photic driving). We report a comparison of simultaneously recorded electric and magnetic data in a photic driving experiment, adapted to the individual alpha rhythm of 10 healthy volunteers. We show that there is a stronger frequency entrainment in magnetoencephalogram than in electroencephalogram recordings in all volunteers, which indicates a possible tangential brain activity underlying the dominant entrainment effect. The entrainment in the magnetoencephalogram lasts over significantly more frequencies and is most effective in the region around the individual alpha and a half alpha. For different channels, we found different degrees of entrainment showing topological and time-varying properties.     

Stochastic resonance in auditory steady-state responses in a magnetoencephalogram

OBJECTIVE: To see whether stochastic resonance can be triggered in the auditory steady-state responses (ASSRs) in a magnetoencephalogram (MEG). METHODS: We measured ASSRs to 1kHz sinusoidal tone modulated at 40Hz with various intensities of white noise and obtained its power and degree of phase synchrony. RESULTS: Group statistics showed a significant enhancement in phase synchrony of ASSR by the presence of white noise of appropriate intensity. Tests on individual subjects showed that the data of four out of nine subjects exhibited enhancements in power or phase synchrony. CONCLUSIONS: The ASSRs exhibit stochastic resonance of the so-called I-type (I for information) shown in phase synchrony when responding to modulated sinusoidal sound superimposed with weak white noise. SIGNIFICANCE: The gamma-band component and other oscillatory components in the brain activity have been recently ascribed by some researchers to the result of stochastic resonance caused by internal noise in the brain. Therefore the presence of stochastic resonance in ASSRs may be evidence to the hypothesis that ASSRs are related to the ongoing gamma-band component.     

The human magnetoencephalogram: some EEG and related correlations.

Simultaneous magnetoencephalographic (MEG) and electroencephalographic (EEG) data were recorded from six normal adult subjects. MEG signal strength and EEG voltage level appear to be linearly correlated. Spectral analysis suggested that the MEG and EEG data were produced by similar but non-identical generator systems. A vertex region magnetic averaged evoked response to flash was recorded in one (of four) subjects, consisting of a waveform similar to but out of phase with the simultaneous EEG averaged evoked response, such that cortical negativity was correlated with a magnetic field directed into the scalp. Eye movement artifact, which can seriously compromise EEG recordings, does not appear to be a major problem in MEG recordings.     

Amygdala activation in affective priming: a magnetoencephalogram study

We employed magnetoencephalography (MEG) to examine amygdala activity during a linguistic affective priming task. The experimental design included positive and negative word pairs. Using synthetic aperture magnetometry in the analysis of MEG data, we identified a left amygdala power increase in the theta frequency range during priming involving negative words. We found that the amygdala displayed a time-dependent intensification in responsiveness to negative stimuli, specifically between 150 and 400 ms after target presentation. This study provides evidence for theta power changes in the amygdala and demonstrates that the analysis of brain oscillations provides a powerful tool to explore mechanisms implicated in emotional processing.     

The effect of saccadic eye movements on the sensor-level magnetoencephalogram

Objective

We used a combination of simulation and recordings from human subjects to characterize how saccadic eye movements affect the magnetoencephalogram (MEG).

Relationship of the magnetoencephalogram to abnormal activity in the electroencephalogram

Summary The EEG and also the MEG were recorded simultaneously from 10 patients with various types of EEG abnormalities; the characteristics of the MEG and its relationship to the EEG were investigated with the use of a digital computer. Examples are shown in which the EEG activity is poorly represented in the MEG and include one configuration of a slow wave with a slow descending limb (intermixed with a more sinusoidal waveform), posterior slow waves and the wave of the 3/sec spike and wave complex. Magnetic theory would suggest that these patterns are associated with dipolar sources oriented radially or perpendicularly to the outer surface of the cortex and each pattern is discussed in relation to this possibility. Examples are shown in which a given pattern is well represented in both MEG and EEG recordings. These include eye-blink artifact, slow waves from a tumor, diffuse theta activity, sinusoidal anterior delta rhythms and the spike of the 3/sec spike and wave complex. Magnetic theory would suggest that these patterns are likely associated with a dipolar source oriented tangentially or parallel to the cortex's surface and each pattern was appropriately discussed. An example is shown of a horizontally oriented delta EEG focus and its corresponding longitudinally oriented magnetic field. The few examples of activity recorded better in the MEG than EEG include some rare instances of slow waves associated with a known tumor, alpha activity in a patient with diffuse delta rhythms and the harmonic components of the 3/sec spike and wave complex. The MEG, as recorded with this particular magnetometer, tending to show diffuse, non-localizable changes associated with localized EEG abnormalities may have its maximum value in helping to determine the dipolar orientation of various EEG waveforms by simultaneously recording the MEG and EEG and also occasionally in its ability to record activity that is not found in the EEG.Supported by Grant 412-13-RD from the Dept. of Mental Health, State of Illinois