The reference problem and mapping of coherence: A simulation study

Summary Four techniques are applied to record EEG signals: bipolar recording, referential recording, common average reference recording and source derivation. For the interpretation of EEG parameter maps knowledge of the properties of the applied recording technique is essential. Bipolar recordings are not discussed in this paper. The application of reference and common average reference recording has the disadvantage of an unknown reference potential. This disadvantage is much larger with the use of source derivation because every electrode signal has its particular reference signal. This must be taken into consideration when coherence estimations are made. With actual EEG records the influence of the reference cannot be determined unambiguously. However, simulation studies enable some essential conclusions. In this paper by means of autoregressive processes EEG signals with given power and coherence properties were simulated and different recording situations using the same data set were reconstructed. The essential result is that computation and mapping of coherences yield the most reliable results when reference recording is used. However, measures to ensure a low reference signal must be taken.     

Prejudgments for Reference Potential Determination to Quantitative EEG Interpretation:Amplitude Distribution and Ear-lobe Activation

This paper presents an automatic techruque of suitable reference potential selection for quantitative EEG interpretation. The 16-channels EEG recording under mono-polar derivation is analyzed. There are two prejudgments defined for checking the amplitude distribution and ear lobe activation. After prejudgments, the EEG is classified into several cases in cluding diffused case, non-diffused case, and artifact contami nation case. Due to the cases, an automatic reference selection method is applied in order to find out suitable reference potential. Finally, the referential derivation constructed according to the obtained reference potential, is evaluated for further EEG rhythm analysis. The presented technique can high light the EEG rhythm of interest,which is useful for quantitative EEG interpretation by both visual inspection and automatic evaluation.     

A new computerized system for electroencephalography at the Kochi Medical School Hospital: the present status and problems of electroencephalogram data filing systems

The usual electroencephalography (EEG) recording consumes great amounts of paper, considerable storage space for records and much time and energy for their search and retrieval. In addition, we can not perform digitized analyses of the records with the present method. To solve these problems, our laboratory developed a new computerized system for EEG, in which data are retained in optic disks, and which has been in service for routine examination since December, 1988. The functions of the system and EEG filing system, include the collection, retention, retrieval, transmission and analyses of data with the reproduction of the original EEG and editing function of summary reports to be filed in the medical records. The summary report consists of summary, characteristic wave patterns picked up and edited from EEG, and spectral array and topographical mapping by digitized analyses of EEG. The condition for the collection of EEG data was 200 Hz/8 bit, and the reproduced wave patterns were accepted by all clinicians. The merits of the system include; (i) saving of paper, space and time needed for EEG, (ii) enabling the comparison of the wave patterns in the form of summary reports and (iii) the capability of digitized analyses of EEG by retaining the EEG data in the data base. The problems remaining to be improved for the system are the longer time required for examination (5-10 min) and the higher running cost (yen 460/order). Regarding the latter problem, a revised method which dispenses with recording paper is under consideration. That is, in the case of screening examinations, summary reports for medical records alone would be delivered to clinicians. This idea has been accepted by some clinicians. To realize the revised system, we presently are planning to establish a method to display EEG on CRT.     

Automatic reference selection for quantitative EEG interpretation: Identification of diffuse/localised activity and the active earlobe reference,iterative detection of the distribution of EEG rhythms

EEG (Electroencephalograph) interpretation is important for the diagnosis of neurological disorders. The proper adjustment of the montage can highlight the EEG rhythm of interest and avoid false interpretation. The aim of this study was to develop an automatic reference selection method to identify a suitable reference. The results may contribute to the accurate inspection of the distribution of EEG rhythms for quantitative EEG interpretation. The method includes two pre-judgements and one iterative detection module. The diffuse case is initially identified by pre-judgement 1 when intermittent rhythmic waveforms occur over large areas along the scalp. The earlobe reference or averaged reference is adopted for the diffuse case due to the effect of the earlobe reference depending on pre-judgement 2. An iterative detection algorithm is developed for the localised case when the signal is distributed in a small area of the brain. The suitable averaged reference is finally determined based on the detected focal and distributed electrodes. The presented technique was applied to the pathological EEG recordings of nine patients. One example of the diffuse case is introduced by illustrating the results of the pre-judgements. The diffusely intermittent rhythmic slow wave is identified. The effect of active earlobe reference is analysed. Two examples of the localised case are presented, indicating the results of the iterative detection module. The focal and distributed electrodes are detected automatically during the repeating algorithm. The identification of diffuse and localised activity was satisfactory compared with the visual inspection. The EEG rhythm of interest can be highlighted using a suitable selected reference. The implementation of an automatic reference selection method is helpful to detect the distribution of an EEG rhythm, which can improve the accuracy of EEG interpretation during both visual inspection and automatic interpretation.     

单通道脑电信号中诱发电位的单次提取

我们正在构建一个脑控拼写装置，直接利用脑信号与计算机进行交互。在这种实时通信模式中，作为通信载体的特征脑信号淹没在自发的脑电背景中，不能采用常规的叠加平均方法来提取，而必须实现特征信号的单次识别。为使这种技术走出实验室，记录脑电的导联数应越少越好。我们采用独特的“模拟自然阅读”诱发模式，让被试从平滑移过小视窗的刺激符号串中识别靶刺激符号，以产生视觉诱发电位（VEP）。利用支持向量机方法，对三名被试位于导联Pz处EEG信号中的VEP进行了单次提取，正确识别率分别为92．1％、94．1％和91．5％，达到了较为满意的效果，为系统的实现打下了基础。     

EmerLoc: location-based services for emergency medical incidents

BACKGROUND: Recent developments in positioning systems and telecommunications have provided the technology needed for the development of location aware medical applications. We developed a system, named EmerLoc, which is based upon this technology and uses a set of sensors that are attached to the patient's body, a micro-computing unit which is responsible for processing the sensor readings and a central monitoring unit, which coordinates the data flow. OBJECTIVE: To demonstrate that the proposed system is technically feasible and acceptable for the potential users. METHOD: Transmission speed is assessed mostly by means of transmission of DICOM compliant images in various operational scenarios. The positioning functionality was established both outdoor using GPS and indoor using the UCLA Nibble system. User acceptability was assessed in a hospital setting by 15 physicians who filled in a questionnaire after having used the system in an experimental setting. RESULTS: Transmission speeds ranged from 88kB/s for a IEEE 802.11 infrastructure to 2.5kB/s for a GSM/GPRS scenario. Positioning accuracy based on GPS was 5-10m. The physicians rated the technical aspects on average above 3 on a 5-point scale. Only the data presentation was assessed to be not satisfactory (2.81 on a 5-point scale). CONCLUSION: The reported results prove the feasibility of the proposed architecture and its alignment with widely established practices and standards, while the reaction of potential users who evaluated the system is quite positive.     

Nonmetallic electrode system for recording EEG and ECG in electromagnetic fields

The construction of a nonmetallic electrode/lead system for recording biopotentials in the presence of electromagnetic fields is described. The system is simple to prefabricate and about as versatile and easy to use as metallic electrodes and connecting wires. It has been used for acute and chronic EEG and ECG recordings from chelonians (turtles and tortoises) with consistently satisfactory results.     

The neurophysiological bases of EEG and EEG measurement: A review for the rest of us

A thorough understanding of the EEG signal and its measurement is necessary to produce high quality data and to draw accurate conclusions from those data. However, publications that discuss relevant topics are written for divergent audiences with specific levels of expertise: explanations are either at an abstract level that leaves readers with a fuzzy understanding of the electrophysiology involved, or are at a technical level that requires mastery of the relevant physics to understand. A clear, comprehensive review of the origin and measurement of EEG that bridges these high and low levels of explanation fills a critical gap in the literature and is necessary for promoting better research practices and peer review. The present paper addresses the neurophysiological source of EEG, propagation of the EEG signal, technical aspects of EEG measurement, and implications for interpretation of EEG data.     

Identifying montages that best detect electrographic seizure activity during polysomnography

STUDY OBJECTIVES: Recognizing epileptic seizures during video polysomnography (VPSG) can be challenging, particularly when using standard, limited EEG montages and paper speed. Few sleep laboratories have PSG equipment that allows for the recording of 18 channels of EEG without compromising the ability to detect sleep apnea, periodic limb movements, and parasomnias. We studied the ability of sleep medicine- and EEG-trained polysomnographers to correctly identify epileptic seizures during PSG using 4, 7, and 18 channels of simultaneous EEG, recording at conventional PSG and EEG paper speeds. The purpose of this study was to determine the value of limited EEG montages viewed with EEG reformatting capability in the identification of seizures during PSG. DESIGN: Blinded EEG analysis of seizures and arousals during VPSG. SETTING: Tertiary care hospital with sleep laboratory and epilepsy monitoring unit. PATIENTS: Subjects with focal (partial) epilepsy that underwent video-EEG monitoring. INTERVENTIONS: We designed two 7-channel EEG montages that might facilitate the identification of seizures arising from the frontal and temporal lobes. Sleep medicine- and EEG-trained polysomnographers were asked to review tracings containing frontal or temporal lobe epileptic seizures and arousals from sleep. Utilizing the capability of our digital recording equipment to reformat EEG channels and change paper speeds, we asked the readers to classify events recorded with 4, 7, and 18 channels of simultaneous EEG, at paper speeds of 10 and 30 mm/sec. MEASUREMENTS AND RESULTS: 6 readers viewed 32 sleep-related events (13 frontal lobe seizures, 11 temporal lobe seizures, and 8 arousals). The following factors were analyzed for their influence on accuracy of event detection: 1) the type of training of the reader (EEG vs. sleep medicine); 2) the number of EEG channels (4, 7, or 18); and 3) paper speed (10 vs. 30 mm/sec). Pair-wise comparisons and generalized estimating equations were used to identify factors leading to more accurate detection of seizures and arousals. 77% of events were correctly identified: 74% of seizures and 88% of arousals. Seizure detection was better using 7 and 18 channels (sensitivity of 82% and 86%, respectively) than 4 EEG channels (sensitivity of 67%) for temporal lobe seizures only. The number of EEG channels did not affect the accuracy of frontal lobe seizure detection. For EEG-trained readers, accuracy was greater using 30 mm/sec than 10 mm/sec paper speed (85% vs. 78% correct, respectively). CONCLUSIONS: Adding EEG channels and EEG reformatting capabilities to PSG interpretation improves the detection of some types of epileptic seizures. Accuracy of temporal lobe seizure detection using an abbreviated 7-channel montage approximates that of an 18-channel EEG recording. However, the same is not true of frontal lobe seizures in which accuracy was similar regardless of the number of EEG channel available. Further studies are needed to identify specific EEG montages that would best detect epileptiform activity during VPSG.     

A description of an accelerometer-based mobility monitoring technique

Accurate monitoring of the mobility status of older adults, over the long-term, is important in rehabilitation medicine, as regular physical activity is central to maintaining both physical and mental health, as well as evaluating quality of life. This technical note describes an accelerometer-based mobility monitoring technique, which can distinguish between static and dynamic activities and can detect the basic postures of sitting, standing and lying. The technique allows thresholds for these postures to be set and two different posture threshold methods are described: mid-point and "best estimate". Preliminary results from using these methods are presented. This preliminary evaluation of the technique was carried out over the long-term (>29 h) in an uncontrolled environment and the method used to carry out the evaluation is described in detail. The two different posture thresholding methods were tested on long-term mobility data from one older adult subject. The subject did not have to follow a specific activity protocol during the recording period (4 days) and was shadowed by an observer in order to evaluate the accuracy of this technique. The monitoring hardware consisted of two accelerometer devices, one on the trunk and the other on the thigh and a pocket-sized ambulatory data-logger. Applying 'best estimate' thresholding, as opposed to mid-point thresholding, improved sitting detection accuracy by 18%, to 93% and lying detection accuracy by 5%, to 84%. Thus, based on these preliminary data, an accurate mobility monitoring system for older adults is described and it was observed that the actual posture threshold limits applied have a high impact on the mobility monitoring system's accuracy and are particularly important for accurately detecting postures when used over the long-term, in an uncontrolled environment.     

New system for recording ambulatory blood pressure in man

A new perfusion and transducer unit for ambulatory blood-pressure recording is described, followed by reports of both the laboratory evaluation of the unit and experience with its clinical use. The major change from earlier systems is the perfusion system, now based on an electrically driven ‘delta’ pump. Pressure is measured by a semiconductor strain-gauge pressure transducer. Laboratory evaluation has shown that the transducer with associated tubing and cannulae has a satisfactory frequency response, considerably better than that of the recording system normally used. Both quantitatively and qualitatively there was a very close correspondence between signals obtained from the entire Oxford system (including recording and replay) and signals obtained directly by means of a catheter-tip transducer. Small, but consistent, signal drifts attributable to battery behaviour are described. The system appears remarkably insensitive to temperature variations within the range of expected ambient temperatures. Delta pump performance is satisfactory, producing essentially constant perfusion rates. Clinically, the system has been used for the recording of ambulatory blood pressures in 110 patients for periods up to 72 h with satisfactory results. Reliability appears good, with minimal artefacts atributable to the equipment. This transducer and perfusion system appears to be fully satisfactory and considerably more reliable than the earlier designs.     

Lokalisierung von EEG-Potentialen unter Berücksichtigung der unterschiedlichen Montagetypen

This article aims to outline the principles of localizing scalp EEG potentials using different EEG montages.Localization of potentials plays a critical role in the clinical EEG interpretation and is based on visual pattern recognition (e. g. epileptiform potentials) and on correct identification of their polarity.In digital EEG recording of EEG signals is performed using a referential derivation, and the recorded signal can be reformatted to different, user-defined montages.Montages are logical and orderly arrangements of EEG channels (i. e. the output of electrode pairs, with a trace representing the amplified potential difference between the two electrodes) that display EEG activity over the entire scalp and allow interpretation of recorded signals of different brain regions.Montages are divided into two large groups, referential and bipolar, denoting the technique by which EEG data are displayed.The article presents different montage types (bipolar, referential, average reference, Laplacian montage). Advantages and limitations of different montages for localization techniques are discussed.Topographic analysis and field mapping of EEG potentials are demonstrated in examples.     

Formative evaluation of a telemedicine model for delivering clinical neurophysiology services part I: Utility,technical performance and service provider perspective

Background

Formative evaluation is conducted in the early stages of system implementation to assess how it works in practice and to identify opportunities for improving technical and process performance. A formative evaluation of a teleneurophysiology service was conducted to examine its technical and sociological dimensions.

Methods

A teleneurophysiology service providing routine EEG investigation was established. Service use, technical performance and satisfaction of clinical neurophysiology personnel were assessed qualitatively and quantitatively. These were contrasted with a previously reported analysis of the need for teleneurophysiology, and examination of expectation and satisfaction with clinical neurophysiology services in Ireland. A preliminary cost-benefit analysis was also conducted.

Results

Over the course of 40 clinical sessions during 20 weeks, 142 EEG investigations were recorded and stored on a file server at a satellite centre which was 130 miles away from the host clinical neurophysiology department. Using a virtual private network, the EEGs were accessed by a consultant neurophysiologist at the host centre for interpretation. The model resulted in a 5-fold increase in access to EEG services as well as reducing average waiting times for investigation by a half. Technically the model worked well, although a temporary loss of virtual private network connectivity highlighted the need for clarity in terms of responsibility for troubleshooting and repair of equipment problems. Referral quality, communication between host and satellite centres, quality of EEG recordings, and ease of EEG review and reporting indicated that appropriate organisational processes were adopted by the service. Compared to traditional CN service delivery, the teleneurophysiology model resulted in a comparable unit cost per EEG.

Conclusion

Observations suggest that when traditional organisational boundaries are crossed challenges associated with the social dimension of service delivery may be amplified. Teleneurophysiology requires a governance and management that recognises its socio-technical nature.

     

Development of a portable multipurpose recorder using a 24-hour ambulatory recorder: Application to polysomnography

With the advance of chronobiology, demands for simultaneous long-term monitoring and recording of various biosignals are increasing. To meet these demands we have developed a protable multipurpose recording system using a 24-hour ambulatory recorder. This technical achievement of less restrictive round-the-clock simultaneous recording of biosignals from not only the circulatory system, but also from the neurological and digestive systems of a subject in his/her daily life will contribute to clinical research on circadian variations of biosignals and EEG analysis during sleep.     

Current neurophysiological tests and revised JSCN technical standards for clinical EEG

The purpose of this lecture is to review the development of current neurophysiology and the revised standard of society for clinical EEG. 1. The improvement of neurophysiological tests. 1) EEG and evoked potential: EEG and evoked potential testing includes the routine EEG recording, EEG monitoring in surgical operation, all night sleep polygraph for the diagnosis of sleep apnea syndrome and many kinds of brain evoked potentials. Especially, the P300 component in the ERP(event-related evoked potential) is useful for the testing of essential brain functions. 2) EMG and evoked EMG: These tests are applied for the diagnosis of neurogenic, myogenic and neuromuscular junction disorder, and also the single fiber EMG using micro needle electrode is useful for the diagnosis of myasthenia gravis. Motor and sensory nerve conduction velocity are calculated from the latency of evoked EMGs. Furthermore, the distribution of these conduction velocities in many nerve fibers is measured by the collision technique. 3) Other tests: Near-infrared spectroscopy for the testing of brain functions has made rapid progress, and the transcranial magnetic stimulation method has come to be used for evaluation of functional diseases in the pyramidal tract, cerebellum and the spinal cord. 2. The revised JSCN technical standards for clinical EEG. The revised recording conditions of ECI(electro cerebral inactivity: flat EEG) in brain death are the focus of this lecture.     

基于单导脑电的数字化新生儿脑功能监护仪的研制

目的新生儿脑功能监护仪大多基于单导脑电设计以适于长时监测.现有的新生儿脑功能监护仪多通过模拟电路以获取振幅整合脑电图(amplitude integratedEEG,aEEG),其体积庞大,价格昂贵,缺少自动分析,在国内应用较少.为降低成本及提高便携性,本文设计了数字化新生儿脑功能监护仪.方法设计包含电极-头皮阻抗检测模块的前置脑电放大电路以采集单导脑电信号,利用基于OMAP-L137的双处理器嵌入式开发板实时计算和显示单导脑电的线性指标 aEEG和非线性指标样本熵(sampleentropy,SampEn),并设计实现用户界面控制和病案数据管理.结果本文设计的监护仪能够实时监控新生儿单导脑电的线性指标 aEEG和非线性指标 SampEn,实现对新生儿脑功能发育及脑损伤的客观、量化的评价.结论该监护仪提取的 aEEG与现有设备具有较好的一致性,脑电的 SampEn为新生儿脑功能判定提供了新的可靠判据,能够更全面地反映新生儿脑功能状况.     

基于心率变异性分析的睡眠分期算法研究和验证

为实现睡眠分期,为穿戴式生理参数监测技术在慢病监测领域的应用提供技术支撑,发展基于心率变异性和支持向量机模型的睡眠分期算法。从心率时间间期序列中提取时域、频域和非线性等86个特征,将多导睡眠图仪的三分类结果(醒、快速眼动期、非快速眼动期)作为“金标准”,采用支持向量机作为多分类器模型;为保证训练集数据质量,使用开放睡眠数据库SHHS中由专家确认挑选的67例PSG样本作为训练集,实现特征筛选和模型参数训练。为验证模型的泛化性能,从SHHS数据库中进一步随机提取939例PSG样本,对模型性能进行测试。睡眠分期模型在训练集上的五折交叉验证的准确率为84.00%±1.33%,卡帕系数为0.70±0.03;在939例测试集上的准确率为76.10%±10.80%,卡帕系数为0.57±0.15。剔除RR间期异常(110例)和明显睡眠结构异常(29例)的样本后,测试集(800例)的准确率为82.00%±5.60%,卡帕系数为0.67±0.14。所提出的基于心率变异性分析的睡眠分期算法具有较高的准确性,大样本人群测试结果表明,该模型具有较好的普适性。     

高共模抑制比全频段脑电采集系统

为了实时消除脑电信号采集过程中引入的直流成分,提高系统的共模抑制比,拓宽信号的采样带宽,设计一款具有动态直流校正功能的全频段脑电采集系统。通过微处理器读取脑电采集系统中所包含的直流成分,然后将直流成分通过数模转换器反馈到实时直流校正系统,接着实时直流校正系统将处理后的直流分量输出至仪用运算放大器的参考端,并和原有的直流分量进行反相相加,从而实现对直流信号的消除。测试结果表明,该脑电采集系统能够实时消除直流成分,将系统共模抑制比提高至120 dB以上,并实现DC～1 000 Hz的全频段脑电信号采集。因此,该系统能够为使用者提供更加精确的脑电信号,可以用于认知科学的研究、医疗诊断等领域,促进相关领域的进一步发展;而且由于系统电路结构相对简单,可以集成到柔性电路板上,制作成可穿戴医疗监护设备,帮助使用者更好地监测自身生理状态。     

myBrain: a novel EEG embedded system for epilepsy monitoring

The World Health Organisation has pointed that a successful health care delivery, requires effective medical devices as tools for prevention, diagnosis, treatment and rehabilitation. Several studies have concluded that longer monitoring periods and outpatient settings might increase diagnosis accuracy and success rate of treatment selection. The long-term monitoring of epileptic patients through electroencephalography (EEG) has been considered a powerful tool to improve the diagnosis, disease classification, and treatment of patients with such condition. This work presents the development of a wireless and wearable EEG acquisition platform suitable for both long-term and short-term monitoring in inpatient and outpatient settings. The developed platform features 32 passive dry electrodes, analogue-to-digital signal conversion with 24-bit resolution and a variable sampling frequency from 250?Hz to 1000?Hz per channel, embedded in a stand-alone module. A computer-on-module embedded system runs a Linux^® operating system that rules the interface between two software frameworks, which interact to satisfy the real-time constraints of signal acquisition as well as parallel recording, processing and wireless data transmission. A textile structure was developed to accommodate all components. Platform performance was evaluated in terms of hardware, software and signal quality. The electrodes were characterised through electrochemical impedance spectroscopy and the operating system performance running an epileptic discrimination algorithm was evaluated. Signal quality was thoroughly assessed in two different approaches: playback of EEG reference signals and benchmarking with a clinical-grade EEG system in alpha-wave replacement and steady-state visual evoked potential paradigms. The proposed platform seems to efficiently monitor epileptic patients in both inpatient and outpatient settings and paves the way to new ambulatory clinical regimens as well as non-clinical EEG applications.