头皮EEG偶极子定位在癫癎外科中的应用研究

目的：研究头皮EEG偶极子定位方法在癫痫手术病人中的应用价值及其准确性。方法：在80例难治性癫痫手术病人中．术前在发作间期头皮EEG上用偶极子定位方法定出致痫源放电位置．术中以皮质电图(ECoG)及脑深部电极记录确定致痫区．对比偶极子定位的准确性．按ECoG定出的位置直接对致痫区进行手术处理．术后随访手术效果。结果：在颞叶癫痫．偶极子定位与ECoG及脑深部电极定位完全一致；在额、顶、枕叶癫痫，偶极子位置误差为10～15mm。随访6～24个月(平均13个月)，80例中71％的病人无癫痫发作，25％的病人发作减少75％以上．手术有效率96%。结论：头皮EEG的偶极子定位方法无创、准确，相当于脑磁图，可避免创伤性检查而用于癫痫病人的术前定位。     

录像脑电图联合偶极子定位法在癫癎外科的应用

目的：探讨顽固性癫癎病人进行录像脑电图（VEEG）监测和偶极子定位法（DLM）在癫癎灶定位的应用与价值。方法：回顾性分析300例顽固性癫癎病人的发作、VEEG检查及偶极子癫癎灶定位的准确性及影响因素。结果：对VEEG的直接人工分析定位率为80％，结合偶极子定位分析准确率可以达到94．3％，且均可以达到与术中皮层脑电图检查定位一致或基本一致。结论：利用128道长程VEEG偶极子定位法是一种方便、无创、准确的癫癎灶定位手段。     

痫样放电偶极子对颞叶内侧型顽固性癫痫的定位价值

目的：探讨痫样放电偶极子分析结合临床特征和其它无创检查对颞叶内侧型顽固性癫痫的定位价值。方法：对21例发作间期主要在颞区存在痴样放电且每月致残性发作1次以上的顽固性癫痫患者,结合临床特征和其它无创检查确诊为颞叶内侧型癫病并定侧后,进行机器人辅助立体定向射频热凝毁损颞叶内侧结构治疗。结果：术后12～37个月,按照Engel分级系统：Ⅰ级6例（29％,其中Ⅰa级5例,Ⅰd级1例）,Ⅱb级3例（14％）,Ⅳa级4例（19％）,Ⅳb级7例（30％）,Ⅳc级1例（5％）。术后患者的神经功能均无明显下降。结论：机器人辅助立体定向系统射频热凝毁损术安全、有效、方便、快捷,部分颞叶内侧型顽固性癫痫患者对立体定向射频热凝治疗反应良好。     

利用小波神经网络求解脑电等效偶极子源参数

提出了多维单尺度径向基小波神经网络的构造性算法 ,并将之应用到脑电等效偶极子源定位问题 ,从而避开对模型系统描述的困难和现有的迭代类求解方法计算时间较长的问题。通过对解空间的随机抽样由正向计算形成学习样本 ,使小波神经网络在训练过程中建立起自己的逆映射联想记忆 ,以正确推断出头皮观测电位与脑内源发生器之间的内在联系 ,使之对于新的脑电数据能实时地、准确地估算出等效偶极子源的参数 ,为脑电的动态分析提供一条途径。计算机仿真计算结果证明了此方法的有效性     

基于真实头模型与多偶极子算法的癫痫致痫灶脑电溯源方法研究

精准定位致痫灶是手术切除致痫灶的前提，而传统基于三维球模型或标准头模型模板的溯源结果与真实致痫灶误差较大。本研究拟在构建真实头模型的基础上，利用癫痫患者睡眠期脑电中的痫性发作棘波，通过多偶极子与真实头模型计算出大脑皮层电流密度分布，对致痫灶进行溯源定位。实验结果表明，基于该算法的溯源结果定位准确率为89.27%，可使植入电极的数量减少（19.34±7.15）%。该方法不仅能够提高致痫灶定位准确性，还能够减少术中额外伤害，为神经外科医生制定手术方案提供了更加直观有效的参考。     

基于混合遗传算法的偶极子源定位的仿真计算

首先提出一种新的混合遗传算法。在基于实数编码的基础上，通过嵌入一个最速下降算子，结合遗传算法和最速下降法两者的优点，并引入模拟退火的思想，即可改善原算法的局部搜索能力，又能进一步提高优化效率。为了验证算法的可行性，通过对脑电偶极子源定位的仿真计算，证明所提出的新算法与其它优化算法相比，在达到最优解的效率上有了明显的提高。     

基于偶极子特征优化的情绪重评同步EEG-fMRI源定位研究

为研究情绪重评时的大脑皮层源活动,针对情绪重评实验范式下采集的15例健康人同步EEG-fMRI数据,首先提出一种新颖的基于偶极子特征优化的融合源定位方法:根据fMRI加权最小范数估计源定位结果,采用20 ms EEG滑动时间窗,提取每个时窗内的偶极子空间融合特征,将其作为动态融合先验进行加权最小范数估计溯源;随后将该结...     

脑磁图在神经外科术前定位的研究进展

1、脑磁图简介MEG是magnetoencephalography的略写,中文译为脑磁图。脑磁图是一种应用脑功能图像检测技术对人体实施完全无接触,无侵袭,无损伤的大脑研究和临床应用设备。它能精确地     

脑电图检查对癫痈病人致痫灶的定位价值

1临床资料1．1一般资料经临床、影像学及脑电图（EEG）检查，明确诊断为癫痫并接受手术者共计96例，其中男60例，女36例，年龄8～49岁，平均28．5岁。发作类型（按1985年中华医学会第一届全国癫痫会议确定的标准）为简单部分性发作6例，复杂部分性发作18例，     

长程视频脑电图监测癫痫发作及在致痫灶定位中的意义

目的：探讨癫痫发作间期和发作期脑电图（EEG）变化特点与发作症状在致痫灶定位中的作用。方法：对80例癫痫患者进行视频脑电图（VEEG）监测,分析其发作间期、发作期EEG特点及临床发作表现作致痫灶定位。结果：80例癫痫患者中,发作间期38例和发作期60例EEG及59例临床发作症状可提供明确的致痫灶定位信息。结论：在致痫灶定位中,发作期与发作间期EEG相比,可提供较高比例的定位信息;综合分析发作问期、发作期EEG和临床发作症状,可以获得大部分癫痫患者致痫灶的定位信息,为放置颅内电极作准确致痫灶定位的重要参考。     

Spike voltage topography and equivalent dipole localization in complex partial epilepsy

Summary The EEG of 45 patients with complex partial epilepsy was recorded from standard and supplementary inferior temporal electrode sites for 2 or more days via cable telemetry onto video (VHS) tape (22–25 channels, common reference). Epochs with "temporal spikes" were read into a topographic EEG device where individual spikes were visually identified and averaged in sums of 8–32. Analysis of spike voltage topography revealed two distinct patterns - dipolar, Type 1 and non-dipolar, Type 2. One or the other spike type predominated in all but two patients. Application of source modeling techniques (3 shells, single dipole, 6 parameters) to the spike topography data revealed that both spike types had similar equivalent dipoles in terms of location and orientation, except for vector elevation. However, calculated dipoles for Type 1 spikes were more stable over the course of the spike peak. Correlations with clinical data and intracranial EEG suggest that Type 1 spikes originate in mesial temporal structures, while Type 2 spikes arise from temporal or frontal neocortex. Spike voltage topography and equivalent dipole localization appear to be useful in the presurgical evaluation of patients with focal epilepsy.Acknowledgements: We appreciate the co-operation of our colleagues, Peter Williamson, Susan Spencer, and Richard Mattson and the assistance of their fellows, Vijay Thidani, Amiram Katz, David Marks, and Richard Scheyer.     

Precision of dipole localization in a spherical volume conductor: A comparison of referential EEG,magnetoencephalography and scalp current density methods

Summary In this study, we determined the influence of dipole orientation, dipole location, and number of recording sites on the precision of dipole localization in a spherical volume conductor. We compared localization from referential EEG (R-EEG), scalp current density EEG (SCD-EEG) and magnetoencephalography (MEG). Dipole orientation had a small influence on the precision of dipole localization for R-EEG and SCD-EEG. Dipole location relative to the recording sites, dipole depth, and number of recording channels strongly influenced the precision of dipole localization. Assuming equal signal to noise conditions for each recording method, MEG and SCD-EEG had a similar precision for dipole localization of a single tangential dipole source and both methods were more precise than R-EEG. However, SCD-EEG was inferior to MEG for distinguishing a single tangential current source from a pair of deeper radial current sources. In summary, these results suggest that the MEG will be most useful for localization of multiple simultaneous dipole sources.     

Clinical application of spike averaging to dipole tracing method

Summary As part of our studies on localization of epileptic foci, dipole analysis using averaged spikes were compared with that using individual spikes for 25 patients with localization related epilepsy. Our results are as follows. 1) In the group which showed stable dipoles from individual spikes, dipole localization from averaged and individual spikes were similar, although the former showed a higher dipolarity and more stable location, for the entire spike discharge including the peak, trough and wave. The high dipolarity was due to improved signal to noise ratio obtained from averaging. 2) The cases with centrotemporal spike focus including benign childhood epilepsy with centrotemporal spikes showed more reliable dipoles. In the cases with frontal lobe epilepsy, reliable dipoles were rarely obtained even with averaged spikes. Each method provided independent information, so they are of complementary value.     

Multimodal estimation of epileptic foci with dipole localization method and other technique

Summary To clarify the diagnostic value of the dipole localization method in estimating the epileptic focus in various types of localization-related epilepsy, dipole analysis of interictal spikes in epileptic patients was performed. Three-layered realistically-shaped models (Scalp-Skull-Brain model, SSB model) were used to compare the results with regional abnormalities revealed by various neuroimaging techniques and clinical manifestations. Subjects were 22 patients with localization-related epilepsy, including 11 cases with localized MRI abnormalities and 9 cases with abnormal SPECT findings. The results of spike dipole location coincided with the clinical findings in 20 of 22 cases. In the two cases with frontal lobe epilepsy, the results did not coincide. In 10 of 11 cases with MRI abnormality dipoles were located within the area of organic lesions. In all 10 cases with SPECT abnormal findings, regional hypoperfusion was found at the area corresponding to the location of the dipole, although SPECT findings showed a wider area as the epileptic focus. In conclusion, dipole estimation using the SSB model can be considered to be a useful technique for noninvasive investigation of epileptic focus.     

Generators of visual evoked potentials for faces and eyes in the human brain as determined by dipole localization

Human visual evoked potentials were recorded during presentation of photos of human and animal faces and various face features. Negative waves with approximate peak latencies of 165 msec (N170) were bilaterally recorded from the occipito-temporal regions. Mean peak latencies of the N170 were shorter for faces than eyes only. Analyses of amplitudes of evoked potentials indicated that the N170 elicited by faces reflected activity of a specific neural system which was insensitive to detailed differences among individual faces regardless of species, and consequently suggest that this system might function to detect existence of faces in general. On the other hand, the mean amplitude of the N170 elicited by human eyes was significantly larger than those by animal eyes. These differences in response latencies and amplitudes of the N170 suggest existence of at least 2 different visual evoked potentials with similar latencies (i.e., N170) which are sensitive to faces in general and human eyes, respectively. Dipole source localization analysis indicated that dipoles for the N170 elicited by eyes were located in the posterior inferior temporal gyrus, and those for faces, located initially in the same region, but moved toward the fusiform and lingual gyri at the late phase of the N170. The results indicated that information processing of faces and eyes separated at least as early as the latency of the N170 at the posterior inferior temporal gyrus as well as the fusiform and lingual gyri, and might provide neurophysiological and anatomical bases to an initial structural encoding stage of human faces.     

The usefulness of the Laplacian in principal component analysis and dipole source localization

Summary Evoked potentials are difficult to analyze because multiple sources are active simultaneously. Principal component analysis and dipole localization are two techniques that have been used to disentangle overlapping sources. Both of these techniques have problems. Principal component analysis suffers from a rotation ambiguity. Dipole localization suffers from biases when the model used to derive the sources from the scalp potentials is misspecified. Using computer simulations we demonstrate that by applying both of these techniques to the Laplacian of the voltages rather than to the raw voltages the problems associated with the two techniques are reduced. Computer programs for the analyses are presented in an Appendix.Supported by grant EY04776 from the National Institutes of Health. We would like to thank Amnon Silverstein for his help with icosohedra.     

Confidence limits for the parameter estimation in the dipole localization method on the basis of spatial correlation of background EEG

Summary A new residual function in the inverse problem of equivalent dipole localization methods is proposed which is based on the spatial correlation of the background EEG. This residual has the advantage that it allows the calculation of confidence limits for dipole model parameters. The method was applied to VEP data, and it was studied how the localization precision depends on the recording time of the EEG. It was found that the tangential position of an equivalent dipole can be located at 99% confidence in a region of the order 7 × 7mm for a head radius of 10cm, while the 99% confidence interval of the depth estimate is approximately 1cm, with a recording time of 20 minutes. It was also observed that an EEG recording time of more than 10–15 minutes is needed to obtain stable localization precision estimates.     

The origins of pattern reversal short latency visual evoked potential as determined by dynamic topography and the dipole tracing method

Summary The generator sites of the parietal P59 and occipital N26 components elicited by hemi-field pattern reversal stimuli were investigated. The topographic distribution of the occipital N26 component showed a paradoxical lateralization, whereas that of the parietal P59 component exhibited an anatomical lateralization. The equivalent dipoles of both occipital N26 and parietal P59 components were situated on the deep mesial surface of the functioning occipital lobe. The differences in these locations were not statistically significant, but the vector moment of the parietal P59 component projected toward the functioning parieto-occipital region and one of the occipital N26 components projected away from the functioning occipital region. The generator sites of the short latency component were considered to differ from those of the middle latency visual evoked potential. Therefore both the occipital pole and the deep cerebral structure, i.e., the lateral geniculate nucleus, may play a role in the generation of equivalent dipoles.This study was supported by the Science Research Promotion Fund of the Japan Private School Promotion Foundation, Kawasaki Medical School Grant No. 1-602, 2-614 for Project Research and the Ministry of Education, Japan, Grants No. 2-759-6009-03881260.