Neurology & clinical neurophysiology : NCN最新文献_第9页

HTS magnetometers for fetal magnetocardiography. 用于胎儿心脏磁图的HTS磁强计。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

Z Li, R T Wakai, D N Paulson, B Schwartz

引用次数: 0

Localization of event-related activity by SAM(erf). 由SAM(erf)定位与事件相关的活动。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

S E Robinson

{"title":"Localization of event-related activity by SAM(erf).","authors":"S E Robinson","doi":"","DOIUrl":"","url":null,"abstract":"Synthetic aperture magnetometry (SAM) has been used to image source power or source signal-to-noise ratio from MEG. However, the locations of maximal event-related oscillatory activity (or changes from resting state) do not necessarily coincide with those sites that are phase-locked to external events (i.e., localized by dipole fit to the averaged evoked response). Since an estimate of the source time-series may also be obtained by applying the beamformer coefficients to the MEG signal, one can image event-related activity by mapping some function reflecting the reliability of the averaged source waveform at each location. We have devised a new analysis method, SAM(erf), for obtaining a functional image of event-related brain activity and revealing the corresponding waveforms for activated sites. The mapping function used is the ratio of RMS amplitude of the averaged source waveform to that of the +/- average waveform, for a selected time window. This function is computed at each coordinate on a three-dimensional grid in the head. In addition to the SAM(erf) functional image, the averaged source waveforms for each local maximum in the image can be computed and displayed. This procedure can reveal multiple locations and waveforms at sites in the brain engaged in event-related activities. When this method is applied to evoked response studies, phase-locked activity can sometimes be found in areas distant from primary sensory cortex. Given the sensitivity of this functional imaging method to areas outside primary sensory cortex, it has the potential for detecting subtle changes in brain activity in health and disease.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"109"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25185831","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Non-invasive electrophysiologic study with amagnetic transesophageal pacing during unshielded multichannel magnetocardiographic mapping. 无屏蔽多通道心脏磁图测图期间经食管磁起搏的无创电生理研究。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

R Fenici, D Brisinda, A M Meloni

{"title":"Non-invasive electrophysiologic study with amagnetic transesophageal pacing during unshielded multichannel magnetocardiographic mapping.","authors":"R Fenici, D Brisinda, A M Meloni","doi":"","DOIUrl":"","url":null,"abstract":"Unlabelled: Multichannel magnetocardiographic (MCG) mapping is a non-invasive method, which can provide reproducible three-dimensional (3D) localization of accessory pathways (AP) and ventricular arrhythmias, before ablation procedures. More recently MCG imaging of intra-atrial reentry circuits has also been reported. So far, reported cases of MCG localization and imaging of arrhythmias were investigated during spontaneous rhythm only, although more relevant information can be obtained during dynamic electrophysiologic study (EPS). For cardiac pacing one could use an amagnetic intracardiac catheter; but this, however, would add invasivity to a non-invasive method. The aim of this study was to validate a novel approach for dynamic non-invasive EPS based on MCG in combination with amagnetic transesophageal pacing (TEP).Method: A tetrapolar 7 French amagnetic catheter was developed, which provides effective TEP (with an average stimulation threshold of 10-15 mA) and simultaneous recording of two esophageal atrial electrograms. MCG data were acquired at rest, with a 36-channel MCG system (sensitivity of 20 fT/Hz(1/2)), for 90 to 300 seconds (sampling rate of 1 KHz; bandwidth of DC Hz to 100 Hz), as a function of the type of pacing procedure. 10 patients were investigated, during both continuous and programmed TEP.Results and conclusions: MCG during TEP was feasible and reproducible. It provided: 1) more accurate localization of AP during pacing-induced maximal preexcitation; 2) inducibility of supraventricular AR and imaging of atrial reentry circuits, not spontaneously present; 3) stabilization of the heart rate to improve the accuracy of quantitative estimate of ventricular repolarization parameters.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"14"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25184980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Continuous head-localization and data correction in a whole-cortex MEG sensor. 全皮质脑磁图传感器的连续头部定位和数据校正。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

H S Wilson

{"title":"Continuous head-localization and data correction in a whole-cortex MEG sensor.","authors":"H S Wilson","doi":"","DOIUrl":"","url":null,"abstract":"Continuous monitoring of the position of a subject's head is an essential part of improving localization accuracy and resolution in MEG. We describe a procedure that has been developed for whole-cortex MEG sensors. The system uses three (or more) small head coils driven continuously by low-amplitude sinusoidal currents with frequencies chosen so they do not interfere with MEG measurements and with each other and are easily separated from power-line signals and harmonics. Analysis of the response of the MEG sensors to the head coils allows continuous monitoring of the position (update times as short as T=2/fpower) using a 3-parameter minimization. The best-fit positions of the head coils are then combined to determine the head translation and rotation. Analysis of phantom data recorded with a 275-channel CTF MEG system in a shielded room shows that coil positions can be determined with an accuracy of approximately 2 mm with an update period T=1/15 s even when the head coils are moving approximately 25 mm at speeds up to 40 mm/s. Data are corrected by expressing the scalar potential for the magnetic field as a spherical-harmonic series, and then determining the effect of rotations and translations on the terms of the series. Since the MEG helmet covers only approximately 60% of the full sphere, care must be taken in determining the coefficients of the spherical-harmonic series to ensure that the modeled magnetic field does not become unrealistically large in the region where there are no MEG sensors (i.e. in the lower 40% of the sphere). Our approach has been to use a minimum-field-energy criterion that minimizes the squared gradient averaged over 4pi sr and radii from 96 to 145 mm while matching the MEG measurements.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"56"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25185583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Dynamic neuromagnetic responses to auditory motion: a novel index for evaluation of attention. 听觉运动的动态神经磁反应:一种评价注意力的新指标。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

J Xiang, S Holowka, R Ishii, D Wilson, S Chuang

{"title":"Dynamic neuromagnetic responses to auditory motion: a novel index for evaluation of attention.","authors":"J Xiang, S Holowka, R Ishii, D Wilson, S Chuang","doi":"","DOIUrl":"","url":null,"abstract":"Our previous studies have demonstrated that there is a motion-related magnetic response evoked by moving sound but not stationary sound. The motion-related response reflects the dynamic activities of brain processing of auditory motion. This study focuses on the effect of attention on the response. Six normal hearing subjects were studied using a 151-channel whole-cortex magnetoencephalography (MEG) system. Four sound stimuli were designed: two sounds moved from left to right (rightward) and the other two sounds moved from right to left (leftward). Two sounds moving in the same direction were separated with an attention task. The attention task was a mathematical calculation. The results showed that when subjects listened to the moving sound, there was a clearly auditory motion related response at a latency of 649 +/- 14.2 ms. However, when subjects were doing the calculation while listening to the moving sounds, the motion related response completely disappeared. Strikingly, there was a dent at a latency of 600 ms. To our knowledge, this is probably the first study showing a neuromagnetic response which can be clearly elicited or inhibited by an attention task. We consider that the motion related response has the potential to be an objective index for the study of attention.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"106"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25184013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Separation of fetal and maternal magnetocardiographic signals in twin pregnancy using independent component analysis (ICA). 使用独立分量分析(ICA)分离双胎妊娠胎儿和母体的心磁图信号。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

M Burghoff, P Van Leeuwen

{"title":"Separation of fetal and maternal magnetocardiographic signals in twin pregnancy using independent component analysis (ICA).","authors":"M Burghoff, P Van Leeuwen","doi":"","DOIUrl":"","url":null,"abstract":"The identification of fetal and maternal signals in magnetocardiograms (MCG) is central to data preprocessing and a prerequisite for data analysis and assessment. This is usually done by creating a template of the signal to be identified and marking data segments correlating to this template before averaging. This procedure is not only cumbersome, but may also lead to problems when there are several overlapping signals of interest such as in MCG recording in single or, more so, in twin pregnancy. Independent component analysis (ICA), which uses higher order statistics to decompose the signal into statistical independent components, has already been used in single pregnancies to distinguish between maternal and fetal signals. We applied the ICA algorithm TDSEP to 9 data sets of twin pregnancies acquired between the 28th and 38th week of pregnancy. Resulting ICA components can be used for further data analysis, e.g., for finding robust triggers or estimating the heart rate and its variability of the twins. The results showed that the maternal and fetal components can be separated from each other as well as from other sources of noise and artifacts. Differences between averaged ICA time curves and averaged raw data are not significant. Limitations include a concurrence of heart rates and changes in signal morphology due to gross movement. Nonetheless, ICA offers a fast and efficient approach for the preprocessing of MCGs with multiple signals of interest.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"39"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25185577","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

How many channels are needed for MEG? MEG需要多少个信道?

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

J Vrba, S E Robinson, J McCubbin

{"title":"How many channels are needed for MEG?","authors":"J Vrba, S E Robinson, J McCubbin","doi":"","DOIUrl":"","url":null,"abstract":"Channel count in modern MEG systems has been steadily increasing, but are more channels necessary? Assuming that the spatial sampling considerations are satisfied, this question can be answered by examining the MEG system's ability to localize and resolve brain sources. For the simple situation where only uncorrelated sensor noise is present, dipole localization accuracy monotonically increases with increasing number of channels, while for spatially correlated brain noise the accuracy increases only until the number of channels reaches 100 to 200. Beyond this limit the inter-channel separation is comparable to the brain noise correlation distance and increasing the channel count does not help. Contrary to the above dipole result, we show by simulations with up to several thousand channels, that if the data is analyzed by beamformers even in the presence of correlated brain noise, the two-source resolvability and single-source localization accuracy monotonically improve with increasing number of channels. We demonstrate such behavior for a 275 channels system, where we have inserted an artificial dipole into real measured brain noise and resampled the number of channels to 138. Beamformer analysis of the data shows markedly improved localization accuracy when the number of channels is increased from 138 to 275. This finding also signifies that the beamformer performance is not limited by system imperfections when the number of channels is as large as 275. To clarify these results, we illustrate analytically the mechanism of beamformer resolution dependence on the number of channels, using an example of a simple system containing two dipole sources, and uncorrelated sensor noise.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"99"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25184122","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

MEG recordings of DC fields using the signal space separation method (SSS). 用信号空间分离法(SSS)记录直流磁场。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

S Taulu, J Simola, M Kajola

{"title":"MEG recordings of DC fields using the signal space separation method (SSS).","authors":"S Taulu, J Simola, M Kajola","doi":"","DOIUrl":"","url":null,"abstract":"Stationary SQUID sensors record time-varying magnetic fields only. Any DC sources, such as magnetic impurities on the scalp or physiological DC currents, are invisible in conventional MEG with stationary sources and sensors. However, movement of the subject relative to the measurement device transforms the DC fields into time-varying MEG signals, which are either signals of interest from biomagnetic sources, or movement artifacts when caused by magnetic residue on the head. These signals can be demodulated to DC by tracking the head movement and by using this recorded information to decompose the signals into a device-independent source model. To do this we have used the signal space separation method (SSS) along with a continuous head position monitoring system. From time variations of the recorded signal, a linear equation is obtained relating the averaged MEG signal variation, the DC-source in the head, and the varying external interference. In this way an unbiased estimate is obtained for the DC source as it is automatically separated from external interference. The method was tested by feeding DC current in an artificial current dipole on a phantom head and by continuously moving and rotating this phantom randomly with a motion amplitude of several centimeters. After the SSS based movement demodulation and reconstruction of the signal from inside of the helmet, the location of the DC current dipole in the phantom could be determined with an accuracy of 2 mm. It is concluded that the method enables localization of DC sources with MEG using voluntary head movements.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"35"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"24895646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

A study of relationship between multifocal VEF responses and binocular disparity. 多焦点VEF反应与双眼视差关系的研究。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

T Owaki, T Takeda

{"title":"A study of relationship between multifocal VEF responses and binocular disparity.","authors":"T Owaki, T Takeda","doi":"","DOIUrl":"","url":null,"abstract":"Multifocal visual evoked magnetic field (mfVEF) is useful for shortening the measurement time and/or improving the signal-to-noise ratio of recording, in investigating cortical activities elicited by multiple stimulus patches across the visual field. To record the whole-head mfVEF, we previously developed custom software to deliver multifocal stimuli and to analyze the acquired data, and we applied it to investigation of stereopsis. In the present study, relationship between mfVEF responses and binocular disparity was investigated. Subjects were instructed to fixate a nonius line in the center of a screen, and they were presented with rapid alteration of random-dot (RD) patches. The experiments consisted of a luminance change condition (condition L) and seven binocular disparity conditions (condition BDs) ranging from a crossed disparity of 1 deg to an uncrossed disparity of 1 deg. Each response evoked by one of the RD patches was obtained with the multifocal technique. Although all subjects showed obvious responses in the condition L, only one of the subjects showed obvious responses in condition BDs. The sources of the responses recorded in condition BDs were mainly localized around calcarine sulci according to the known retinotopic cortical representation. The responses obtained in condition BDs showed dependence on binocular disparity in the magnitude and the latency. These results would be the basis for further analysis of brain magnetic responses related to stereopsis.","PeriodicalId":83814,"journal":{"name":"Neurology & clinical neurophysiology : NCN","volume":"2004 ","pages":"107"},"PeriodicalIF":0.0,"publicationDate":"2004-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"24895650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

A sensor configuration for a 304 SQUID vector magnetometer. 304 SQUID矢量磁力计的传感器配置。

Neurology & clinical neurophysiology : NCN Pub Date : 2004-11-30

A Schnabel, M Burghoff, S Hartwig, F Petsche, U Steinhoff, D Drung, H Koch

引用次数: 0