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PubMed1997

Assessment of digital EEG, quantitative EEG, and EEG brain mapping: report of the American Academy of Neurology and the American Clinical Neurophysiology Society [RETIRED].

A. Digital EEG is an established substitute for recording, reviewing, and storing a paper EEG record. It is a clear technical advance over previous paper methods. It is highly recommended. (Class III evidence, Type C recommendation). B. EEG brain mapping and other advanced QEEG techniques should be used only by physicians highly skilled in clinical EEG, and only as an adjunct to and in conjunction with traditional EEG interpretation. These tests may be clinically useful only for patients who have been well selected on the basis of their clinical presentation. C. Certain quantitative EEG techniques are considered established as an addition to digital EEG in: C.1. Epilepsy: For screening for possible epileptic spikes or seizures in long-term EEG monitoring or ambulatory recording to facilitate subsequent expert visual EEG interpretation. (Class I and II evidence, Type A recommendation as a practice guideline). C.2. OR and ICU monitoring: For continuous EEG monitoring by frequency-trending to detect early, acute intracranial complications in the OR or ICU, and for screening for possible epileptic seizures in high-risk ICU patients. (Class II evidence, Type B recommendation as a practice option). D. Certain quantitative EEG techniques are considered possibly useful practice options as an addition to digital EEG in: D.1. Epilepsy: For topographic voltage and dipole analysis in presurgical evaluations. (Class II evidence, Type B recommendation). D.2. Cerebrovascular Disease: Based on Class II and III evidence, QEEG in expert hands may possibly be useful in evaluating certain patients with symptoms of cerebrovascular disease whose neuroimaging and routine EEG studies are not conclusive. (Type B recommendation). D.3. Dementia: Routine EEG has long been an established test used in evaluations of dementia and encephalopathy when the diagnosis remains unresolved after initial clinical evaluation. In occasional clinical evaluations, QEEG frequency analysis may be a useful adjunct to interpretation of the routine EEG when used in expert hands. (Class II and III evidence as a possibly useful test, Type B recommendation). E. On the basis of current clinical literature, opinions of most experts, and proposed rationales for their use, QEEG remains investigational for clinical use in postconcussion syndrome, mild or moderate head injury, learning disability, attention disorders, schizophrenia, depression, alcoholism, and drug abuse. (Class II and III evidence, Type D recommendation). F. On the basis of clinical and scientific evidence, opinions of most experts, and the technical and methodologic shortcomings, QEEG is not recommended for use in civil or criminal judicial proceedings. (Strong Class III evidence, Type E recommendation). G. Because of the very substantial risk of erroneous interpretations, it is unacceptable for any EEG brain mapping or other QEEG techniques to be used clinically by those who are not physicians highly skilled in clinical EEG interpretation. (Strong Class III evidence, Type E recommendation).

Brain↗

PubMed2005

EEG and intelligence: relations between EEG coherence, EEG phase delay and power.

OBJECTIVE: There are two inter-related categories of EEG measurement: 1, EEG currents or power and; 2, EEG network properties such as coherence and phase delays. The purpose of this study was to compare the ability of these two different categories of EEG measurement to predict performance on the Weschler Intelligence test (WISC-R). METHODS: Resting eyes closed EEG was recorded from 19 scalp locations with a linked ears reference from 442 subjects aged 5-52 years. The Weschler Intelligence test was administered to the same subjects but not while the EEG was recorded. Subjects were divided into high IQ (> or = 120) and low IQ (< or = 90) groups. EEG variables at P<.05 were entered into a factor analysis and then the single highest loading variable on each factor was entered into a discriminant analysis where groups were high IQ vs. low.Q. RESULTS: Discriminant analysis of high vs. low IQ was 92.81-97.14% accurate. Discriminant scores of intermediate IQ subjects (i.e. 90 < IQ < 120) were intermediate between the high and low IQ groups. Linear regression predictions of IQ significantly correlated with the discriminant scores (r = 0.818-0.825, P < 10(-6)). The ranking of effect size was EEG phase > EEG coherence > EEG amplitude asymmetry > absolute power > relative power and power ratios. The strongest correlations to IQ were short EEG phase delays in the frontal lobes and long phase delays in the posterior cortical regions, reduced coherence and increased absolute power. CONCLUSIONS: The findings are consistent with increased neural efficiency and increased brain complexity as positively related to intelligence, and with frontal lobe synchronization of neural resources as a significant contributing factor to EEG and intelligence correlations. SIGNIFICANCE: Quantitative EEG predictions of intelligence provide medium to strong effect size estimates of cognitive functioning while simultaneously revealing a deeper understanding of the neurophysiological substrates of intelligence.

Adolescent↗

PubMed1994

[The baseline EEG traits and the induced EEG changes by chronic antidepressant medication in patients with major depression. Early prediction of clinical outcomes solely based on quantification and mapping of EEG].

Forty patients of typical major depression (DSM-III-R) have been adopted for the present study. Hamilton Rating Scale for Depression (HAM-D) was used for the clinical assessment of depressive symptoms, and the patients were followed up at least for four weeks. All the patients were confirmed to be right-handed. The baseline EEGs were compared with age-matched normal subjects (N = 38; all right handed). The differences between depressive patients and normal subjects were less theta activity, more fast activity in anterior part of both hemispheres and in posterior part of the right hemisphere in the depressive patients than in the normal subjects. As a preliminary study, amitriptyline 25 mg was single dose administered and EEGs were recorded before and 1, 3 and 6 hours after the first drug administration in normal male volunteers (N = 6; right-handed). EEG changes of after the medication from the baseline were significant increase of theta and decrease of alpha activity, increase of beta activity was not significant changes. Particularly EEG changes of after 3 hour's administration showed the typical thymoleptic reaction type. EEG changes in patients from the baseline EEG after the first medication were similar to normal subjects. The patients (N = 21) were divided into two groups based on the changes of HAM-D score during four-weeks' treatment; therapy-responsive and therapy-resistant groups. EEG changes after the first single dose administrations in the former were compared with the latter of two patients' groups. Both groups have shown an increase of theta and a decrease of alpha activity. There was more evident alpha increase in therapy-responsive patients than in therapy-resistant ones. However, there were significant differences in amitriptyline-induced EEG changes particularly in beta frequency band; therapy-responsive group showed an increase of beta activity, while therapy-resistant showed no or little change. Using discriminant analysis, the overall hitting ratio of the EEG prediction for therapy-responsive and therapy-resistant group was calculated as 85% at 3 hours after the initiation of antidepressant medication. If EEG mapping, particularly the mapping of differences between pre- and post-drug EEGs, is used to illustrate the EEG responses against antidepressant medication, it will be quite useful to discriminate therapy-resistant patients from therapy-responsive ones in very early stage of the drug treatment.

Adult↗

PubMed2006

The EEG assessment of low-grade hepatic encephalopathy: comparison of an artificial neural network-expert system (ANNES) based evaluation with visual EEG readings and EEG spectral analysis.

OBJECTIVE: The EEG provides an objective staging of hepatic encephalopathy (HE), but its interpretation may be biased by inter-observer variability. This study aims at comparing an entirely automatic EEG classification of HE based on an artificial neural network-expert system procedure (ANNES) with visual and spectral analysis based EEG classifications. METHODS: Two hundred and thirty-eight consecutive cirrhotic patients underwent closed-eye EEG. They were followed up for up to one-year to detect bouts of overt HE and death. The EEG was classified by ANNES, qualitative visual reading, main basic rhythm frequency and spectral analysis. The classifications were assessed on the basis of: (i) match with liver function, (ii) prognostic value and (iii) repeatability. RESULTS: All classifications were found to be related to the severity of liver failure, with cognitive findings and a history of previous bouts of HE. All of them had prognostic value on the occurrence of overt HE and on survival. The ANNES based classification was more repeatable than the qualitative visual one, and had the advantage of detecting low power EEG, but its efficiency in analyzing low-grade alterations was questionable. CONCLUSIONS: An entirely automatic - ANNES based - EEG classification of HE can improve the repeatability of EEG assessment, but further improvement of the device is required to classify mild alterations. SIGNIFICANCE: The ANNES based EEG grading of HE needs further improvements to be recommended in clinical practice, but it is already sufficient for detecting normal and clearly altered EEG tracings.

Electroencephalography↗

PubMed1977

EEG and haemodialysis. A structural survey of EEG spectral analysis, Hjorth's EEG descriptors, blood variables and psychological data.

Computerized EEG was performed in 20 patients with renal failure before and after haemodialysis (HD), applying spectral analysis and Hjorth's EEG descriptors in EEG quantification, correlation and factor analysis as statistical procedures to analyse the connections of EEG, blood variables and psychological performance. The main results were: (1) Moderate uraemic encephalopathy -- according to Kiley's (1971) standards -- was present in most of our patients, before and after HD. (2) Before HD, EEG slowing was most strongly connected with the creatinine level and EEG acceleration with hyperkalaemia, which in most cases accompanied a high urea level. (3) Significant EEG changes after HD were: decrease of percentage delta activity, increase of Hjorth's 'mobility', decrease of Hjorth's 'complexity'. (4) The theta/alpha ratio (Matousek 1968) was significantly correlated with the patient's general clinical state after HD. (5) Visual discrimination, memory and maximal tapping speed improved significantly after HD. Only Hjorth's EEG parameters were correlated with test performance in that patients with low voltage and fast EEGs did worse in visual discrimination.

Adult↗

PubMed2006

EEG-fMRI of epileptic spikes: concordance with EEG source localization and intracranial EEG.

Simultaneous EEG and fMRI recordings permit the non-invasive investigation of the generators of spontaneous brain activity such as epileptic spikes. Despite a growing interest in this technique, the precise relationship between its results and the actual regions of activated cortex is not clear. In this study, we have quantified for the first time the concordance between EEG-fMRI results and stereotaxic EEG (SEEG) recordings in 5 patients with partial epilepsy. We also compared fMRI and SEEG with other non-invasive maps based on scalp EEG alone. We found that SEEG measures largely validated the results of EEG and fMRI. Indeed, when there is an intracranial electrode in the vicinity of an EEG or fMRI peak (in the range 20-40 mm), then it usually includes one active contact. This was the case for both increases ('activations') and decreases ('deactivations') of the fMRI signal: in our patients, fMRI signal decrease could be as important in understanding the complete picture of activity as increase of fMRI signal. The concordance between EEG and fMRI was not as good as the concordance between either of these non-invasive techniques and SEEG. This shows that the two techniques can show different regions of activity: they are complementary for the localization of the areas involved in the generation of epileptic spikes. Moreover, we found that the sign of the fMRI response correlated with the low frequency content of the SEEG epileptic transients, this latter being a reflection of the slow waves. Thus, we observed a higher proportion of energy in the low frequencies for the SEEG recorded in regions with fMRI signal increase compared to the regions with fMRI signal decrease. This could reflect an increase of metabolism linked to the presence of slow waves, which suggests that fMRI is a new source of information on the mechanisms of spike generation.

Brain Mapping↗

PubMed1991

[Epilepsy with laughing seizures, hypothalamic hamartoma and precocious puberty. Contributions of MRI, computed EEG topography (CET) and ambulatory EEG (A-EEG)].

The concurrence of gelastic (laughing) seizures, hypothalamic hamartoma and precocious puberty constitutes a well defined epileptic syndrome in children; moreover mental retardation, neuropsychological deterioration and behavioral disorders have been often observed in these patients. In two cases we studied by means of MRI the appearance and the site of the hamartoma (in the posterior part of the hypothalamus with extension toward the third ventricle). The EEG study was performed by means of repeated recordings, of Computed EEG Topography (CET) and of Ambulatory EEG (A-EEG): in both patients during interictal periods paroxysmal EEG discharges prevailing in temporal or fronto-temporal regions and slight abnormalities of the background activity in the same areas were detected. Laughing seizures were recorded in each patient particularly by means of A-EEG: in case 1 bursts of high-voltage activity ("theta" waves) followed by depression of the background rhythm and by irregular spike discharges located in left temporal region were observed; in patient 2 irregular generalised spike discharges followed by slow waves or by depression of the background activity were seen. The presence of local abnormalities in both patients can support the hypothesis that the cortex, especially of the temporal anterior lobe, is involved in the origin of the laughing seizures. The significance of the mechanisms of secondary generalization as regards the seriousness of the epilepsy and of the mental impairment in these patients is also suggested.

Brain Mapping↗

PubMed1979

Is a man, a man, a man? (or: is an EEG, an EEG, an EEG?) some remarks on the homogeneity of "normal subjects".

Many studies involving computerized EEG analyses are based on the assumption that normal subjects constitute a homogeneous population, so that under specified conditions across-subject averaging is justified. Quite often EEG signals are processed with little or no concern for the state of the particular person from whom they are obtained. It is the purpose of this discussion to draw attention to the fact that only can normals have different EEG's one from another, but also that the same ones can display markedly different EEGs from recording session to recording session. A consequence of this situation is that there is always a large between-subject variability, and that the source of the signals needs to be carefully documented before generalizations can be made.

Adult↗

PubMed1981

[Characterization of genetic EEG-variations with the amplitude-interval-analysis. I. Variations of alpha-activity; flat-EEG; borderline flat EEG, occipital slow beta-waves; monotonous alpha-rhythm (author's transl)].

In 121 healthy adult male probands with different variants of alpha-activity (monotonous alpha-waves; low voltage EEG, borderline low voltage EEG; occipital slow beta-waves) a quantitative description of unipolar leads was carried out using a program for amplitude-interval (time-domain) analysis. Statistically significant differences between means of the examined parameters were discovered between the various EEG variants. No single parameter, however, separates these variants reliably. For such a separation, methods of multivariate statistics will have to be used. Significant differences between right and left hemispheres (primarily lower alpha-activity together with higher beta-activity on the left hemisphere) were found in all EEG types examined except the variant with monotonous alpha-waves.

Alpha Rhythm↗

PubMed2006

Which electroencephalography (EEG) for epilepsy? The relative usefulness of different EEG protocols in patients with possible epilepsy.

BACKGROUND AND AIMS: Electroencephalography (EEG) is an essential investigative tool for use in young people with epilepsy. This study assesses the effects of different EEG protocols on the yield of EEG abnormalities in young people with possible new epilepsy. METHODS: 85 patients presenting to the unit underwent three EEGs with differing protocols: routine EEG (r-EEG), sleep-deprived EEG (SD-EEG), EEG carried out during drug-induced sleep (DI-EEG). The yield of EEG abnormalities was compared using each EEG protocol. RESULTS: 98 patients were recruited to the study. Of the 85 patients who completed the study, 33 (39%) showed no discernible abnormality on any of their EEG recordings. 36 patients (43%) showed generalised spike and wave during at least one EEG recording, whereas 15 (18%) had a focal discharge evident at some stage. SD-EEG had a sensitivity of 92% among these patients, whereas the sensitivity of DI-EEG and r-EEG was 58% and 44%, respectively. The difference between the yield from SD-EEG was significantly higher than that from other protocols (p < 0.001). Among the 15 patients showing focal discharges, SD-EEG provoked abnormalities in 11 (73%). r-EEG and DI-EEG each produced abnormalities in 40% and 27%, respectively. 7 patients (47%) had changes seen only after sleep deprivation. In 2 (13%), the only abnormalities were seen on r-EEG. In only 1 patient with focal discharges (7%) was the focal change noted solely after drug-induced sleep. These differences did not reach significance. CONCLUSION: EEG has an important role in the classification of epilepsies. SD-EEG is an easy and inexpensive way of increasing the yield of EEG abnormalities. Using this as the preferred protocol may help reduce the numbers of EEGs carried out in young patients presenting with epilepsy.

Adolescent↗

PubMed1997

Association of combined MRI, interictal EEG, and ictal EEG results with outcome and pathology after temporal lobectomy.

PURPOSE: Magnetic resonance imaging, interictal scalp EEG, and ictal scalp EEG each have been shown to localize the primary epileptic region in most patients with mesial-basal temporal lobe epilepsy (MBTLE), but the association of surgical outcome and pathology with each combination of these test results is not known. METHODS: We reviewed the MRI, interictal scalp EEG, and ictal scalp EEG results of 90 consecutive patients with MBTLE. Twelve patients were excluded from the analysis because inconclusive bitemporal intracranial EEG results precluded anterior temporal lobectomy (ATL); none had concordant MRI and interictal scalp EEG results. We compared all combinations of presurgical MRI, interictal EEG, and ictal EEG results to seizure outcome and tissue pathology in the 78 patients who underwent an ATL. RESULTS: Forty-eight (61%) patients had concordant lateralized MRI and interictal EEG temporal lobe abnormalities, with no discordant ictal EEG results; 77% of these patients were seizure-free after ATL. Concordance of MRI and interictal EEG abnormalities correlated with seizure cessation (p < 0.05), compared to all combinations with discordant or nonlateralizing MRI and interictal EEG results. Mesial temporal sclerosis (MTS) was confirmed pathologically in about 80% of both groups (p = 0.5). Outcome in patients with concordant MRI and ictal EEG with nonlateralizing interictal EEG was significantly worse than combinations with concordant MRI and interictal EEG (p < 0.02). CONCLUSIONS: Compared to other combinations of test results, concordance of MRI and interictal EEG is most closely associated with surgical outcome in MBTLE. However, most selected patients have pathologic confirmation of MTS regardless of test results or outcome. This information may be useful for planning the presurgical evaluation of patients with medically intractable MBTLE.

Adolescent↗

PubMed1992

Automatic EEG interpretation: a new computer-assisted system for the automatic integrative interpretation of awake background EEG.

A new computer-assisted system for automatic interpretation of the awake electroencephalogram (EEG) was developed. First, all the items necessary for EEG interpretation were determined in accordance with the procedure that a qualified electroencephalographer (EEGer) goes through for the visual inspection of the background EEG activity, and then each item was defined quantitatively. For the automatic interpretation, specific EEG parameters were determined for each item so that they could fit the graded judgement of the item by the qualified EEGer as closely as possible. These specific EEG parameters were actually calculated from periodograms obtained from the time series of EEG records of 14 patients with various neurological diseases. The automatic EEG interpretation system thus established was applied to the EEG data of these 14 subjects and to 3 additional EEGs, and the results were compared with those obtained through the visual interpretation by the EEGer. This automatic EEG interpretation was found to be in good agreement with the visual interpretation by the EEGer in most EEG records. In contrast with the previous automatic analyses of EEG which were focussed on certain aspects of EEG such as the dominant rhythm, the present system is unique in its capability of providing an integrative interpretation of the spontaneous awake EEG by taking into account all its features except for paroxysmal abnormalities.

Adult↗

PubMed1981

EEG in phenylketonuria. Attempt to establish clinical importance of EEG changes.

To determine the importance of an abnormal EEG in phenylketonuria (PKU), we reviewed 137 EEGs from 48 patients with PKU. Patients were divided into three groups: group 1 (n = 14) had only normal EEGs, group 2 (n = 20) had only abnormal EEGs, and group 3 (n = 14) initially had normal EEGs that later became abnormal. The most common EEG abnormality was focal paroxysmal discharge. Patients in group 2 started treatment at a later age an had a greater frequency of seizures and mental retardation. Phenylalanine levels greater than 20 mg/dL were more often associated with abnormal EEGs. Older patients were more likely to have abnormal EEGs; 78% of the 41 patients who had EEGs at age 6 or older had abnormal records, whereas only 15% of the 26 patients who had EEGs before the age of 6 had abnormal records. Conventionally treated patients with classic PKU and normal EEGs in infancy may have abnormal EEGs when retested later even though they remain on a restricted diet. Although not usually associated with clinical deterioration, abnormal EEGs may unveil the presence of CNS dysfunction even when a child is in satisfactory clinical condition.

Adolescent↗

PubMed1986

Visually and auditory evoked EEG potentials in carriers of four hereditary EEG variants.

Visually and auditory evoked EEG potentials were studied in 248 healthy university students, who were carriers of one of the following hereditary EEG variants: Monomorphic alpha-waves; low-voltage-EEG; EEG in which the alpha-rhythm was mixed diffusely with beta-waves; and EEG with fronto-precentral beta-groups. The study uncovered consistent and statistically significant group differences between the EEG-countertypes, monomorphic alpha-waves and the low-voltage EEG: subjects with monomorphic alpha-waves showed higher amplitudes and longer latencies of most peaks of the visually evoked potential (VEP), and higher amplitudes for most peaks of the auditory evoked potentials (AEP). Similar differences between EEG types were shown for two measures--overall amplitude (oscillation) and average latency--of all peaks for VEPs and AEPs. The results are consistent with a hypothesis discussed in an earlier paper in which differences between these two EEG types in processing of information in the CNS were assumed on the basis of psychological test results and neurophysiological theory. The two EEG types with beta-waves in addition to alpha-waves showed latencies of evoked potentials in-between those found in the EEG types with monomorphic alpha-waves, on the one hand, and the low-voltage EEG on the other. There was no significant difference in the frequency of VEP augmenters and reducers between EEG types.

Adult↗

PubMed1983

EEG topogram--an aid in describing EEG to the clinician.

The investigation presents a simple, reliable method to show localized EEG abnormalities in a topographical display. The aim of the study was to find a method which could be used in clinical practice, and which in topographical form could complement the written EEG report with information about degree and localization of an EEG abnormality. The EEG was recorded on a 21-channel polygraph (Siemens-Elema). The source derivation recording technique was used. Besides being displayed as a conventional EEG record, the signals were fed to a small computer that calculated an abnormality feature based on the time domain descriptors activity, mobility and complexity. Obtained values were converted into ink density in topograms by modulating the displacement velocity of the ink jet beam. The dynamic range was chosen so that maximum and minimum densities represented 1.5 and 0.5 times the average for each descriptor. The ink density in the topogram was thus related to the degree of EEG abnormality. The recording procedure followed the ordinary clinical routine except that the conventional EEG display was interrupted several times for a few seconds, on command by the EEG technician, to write out the topogram on the EEG paper. It is concluded that EEG topograms produced on line as part of the EEG examination procedure may greatly enhance EEG information conveyed from the neurophysiologist to the clinician. Furthermore, they permit direct visual comparison with other diagnostic topographic displays such as CT scan.

Brain↗

PubMed1992

EEG power changes are more sensitive than spectral edge frequency variation for detection of cerebral ischemia during carotid artery surgery: a prospective assessment of processed EEG monitoring.

To investigate the basis of ambiguous reports of the validity and utility of processed electroencephalogram (EEG) detection of cerebral ischemia, 19 patients monitored during surgical procedures requiring clamping of the carotid artery were studied. The EEG was recorded and observed for detection of alteration of spectral edge frequency versus EEG power. Electrodes were positioned at the P3-C3' locations over the left hemisphere and P4-C4' areas over the right hemisphere (10-20 system of electrode placement). Maximum sensitivity was used for recordings of the processed EEG. Twelve of 19 patients had bilateral carotid vascular stenosis. Nine of 19 patients studied with EEG monitoring had EEG changes suggestive of cerebral ischemia during interruption of carotid artery blood flow by surgical manipulation, defined as a decline in EEG power of greater than 40% or a decline in spectral edge frequency of at least 3 Hz. Eight of these episodes occurred at the time of carotid vascular clamp placement. These changes were confirmed by the raw EEG. Whereas power band monitoring detected 9 episodes of suspected ischemia, alteration of spectral edge frequency was sufficient to detect only 2 of these episodes. One patient sustained a right hemispheric stroke detected intraoperatively by a 47% decline in EEG power; however, these changes were unaccompanied by intraoperative alteration of spectral edge frequency. It is concluded that monitoring of EEG power with processed EEG devices is a more sensitive indicator of cerebral ischemia than monitoring only the spectral edge frequency of the EEG.

Aged↗

PubMed2006

Effects of fMRI-EEG mismatches in cortical current density estimation integrating fMRI and EEG: a simulation study.

OBJECTIVE: Multimodal functional neuroimaging by combining functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) has been studied to achieve high-resolution reconstruction of the spatiotemporal cortical current density (CCD) distribution. However, mismatches between these two imaging modalities may occur due to their different underlying mechanisms. The aim of the present study is to investigate the effects of different types of fMRI-EEG mismatches, including fMRI invisible sources, fMRI extra regions and fMRI displacement, on the fMRI-constrained cortical imaging in a computer simulation based on realistic-geometry boundary-element-method (BEM) model. METHODS: Two methods have been adopted to integrate the synthetic fMRI and EEG data for CCD imaging. In addition to the well-known 90% fMRI-constrained Wiener filter approach (Liu AK, Belliveau JW, Dale AM. PNAS 1998;95:8945-8950.), we propose a novel two-step algorithm (referred to as 'Twomey algorithm') for fMRI-EEG integration. In the first step, a 'hard' spatial prior derived from fMRI is imposed to solve the EEG inverse problem with a reduced source space; in the second step, the fMRI constraint is removed and the source estimate from the first step is re-entered as the initial guess of the desired solution into an EEG least squares fitting procedure with Twomey regularization. Twomey regularization is a modified Tikhonov technique that attempts to simultaneously minimize the distance between the desired solution and the initial estimate, and the residual errors of fitness to EEG data. The performance of the proposed Twomey algorithm has been evaluated both qualitatively and quantitatively along with the lead-field normalized minimum norm (WMN) and the 90% fMRI-weighted Wiener filter approach, under repeated and randomized source configurations. Point spread function (PSF) and localization error (LE) are used to measure the performance of different imaging approaches with or without a variety of fMRI-EEG mismatches. RESULTS: The results of the simulation show that the Twomey algorithm can successfully reduce the PSF of fMRI invisible sources compared to the Wiener estimation, without losing the merit of having much lower PSF of fMRI visible sources relative to the WMN solution. In addition, the existence of fMRI extra sources does not significantly affect the accuracy of the fMRI-EEG integrated CCD estimation for both the Wiener filter method and the proposed Twomey algorithm, while the Twomey algorithm may further reduce the chance of occurring spurious sources in the extra fMRI regions. The fMRI displacement away from the electrical source causes enlarged localization error in the imaging results of both the Twomey and Wiener approaches, while Twomey gives smaller LE than Wiener with the fMRI displacement ranging from 1-2 cm. With less than 2 cm fMRI displacement, the LEs for the Twomey and Wiener approaches are still smaller than in the WMN solution. CONCLUSIONS: The present study suggests that the presence of fMRI invisible sources is the most problematic factor responsible for the error of fMRI-EEG integrated imaging based on the Wiener filter approach, whereas this approach is relatively robust against the fMRI extra regions and small displacement between fMRI activation and electrical current sources. While maintaining the above advantages possessed by the Wiener filter approach, the Twomey algorithm can further effectively alleviate the underestimation of fMRI invisible sources, suppress fMRI spurious sources and improve the robustness against fMRI displacement. Therefore, the Twomey algorithm is expected to improve the reliability of multimodal cortical source imaging against fMRI-EEG mismatches. SIGNIFICANCE: The proposed method promises to provide a useful alternative for multimodal neuroimaging integrating fMRI and EEG.

Analysis of Variance↗

PubMed1998

Evaluation of acute ischemic stroke using quantitative EEG: a comparison with conventional EEG and CT scan.

The sensitivity of quantitative electroencephalogram (EEG) was compared with that of conventional EEG in patients with acute ischaemic stroke. In addition, a correlation between quantitative EEG data and computerized tomography (CT) scan findings was carried out for all the areas of lesion in order to reassess the actual role of EEG in the evaluation of stroke. Sixty-five patients were tested with conventional and quantitative EEG within 24 h from the onset of neurological symptoms, whereas CT scan was performed within 4 days from the onset of stroke. EEG was recorded from 19 electrodes placed upon the scalp according to the International 10-20 System. Spectral analysis was carried out on 30 artefact-free 4-sec epochs. For each channel absolute and relative power were calculated for the delta, theta, alpha and beta frequency bands and such data were successively represented in colour-coded maps. Ten patients with extensive lesions documented by CT scan were excluded. The results indicated that conventional EEG revealed abnormalities in 40 of 55 cases, while EEG mapping showed abnormalities in 46 of 55 cases: it showed focal abnormalities in five cases and nonfocal abnormalities in one of six cases which had appeared to be normal according to visual inspection of EEG. In a further 11 cases, where the conventional EEG revealed abnormalities in one hemisphere, the quantitative EEG and maps allowed to further localize abnormal activity in a more localized way. The sensitivity of both methods was higher for frontocentral, temporal and parieto-occipital cortical-subcortical infarctions than for basal ganglia and internal capsule lesions; however, quantitative EEG was more efficient for all areas of lesion in detecting cases that had appeared normal by visual inspection and was clearly superior in revealing focal abnormalities. When we considered the electrode related to which the maximum power of the delta frequency band is recorded, a fairly close correlation was found between the localization of the maximum delta power and the position of lesions documented by CT scan for all areas of lesion excepting those located in the striatocapsular area.

Acute Disease↗