Electroencephalography and clinical neurophysiology最新文献

Spectral features of EEG background activity were studied in patients with localized symptomatic epilepsy (LSE), with origin in the frontal or temporal lobes. Z-values of high resolution spectra and measures of the parametric (ξα) model of the EEG were obtained for all 10/20 System leads and were compared with those obtained in a control group. Comparisons were performed between syndromic variants of LSE and between subgroups of patients with or without paroxysmal activity in their digital EEGs (dEEG). Marked reduction of the energy in the alpha range and a mild increase in the theta range were found in the patients, unrelated to the syndromic variant of the epilepsy. These deviations from normality were widespread on the scalp and were not related to antiepileptic medication. Non-parametric testing showed a positive correlation between the magnitude of the quantitative EEG abnormalities and the amount of paroxysmal activity in the dEEG. Slowing of the mean frequency of alpha components of the spectra, an actual decrease of power in the alpha range and an increase in the theta range explained the results. The most striking finding of this paper is that focal epileptogenesis may have a generalized impact in the frequency composition of EEG.

In this study, piezoelectric polyvinylidenefluoride (PVDF) wire was used in construction of a transducer for recording of respiration. The recordings have been performed in 202 subjects, mainly during normal routine electroencephalography (EEG) examinations. Comparison of the PVDF wire transducer with the piezoelectric Siemens Movement Sensor 230 was performed. The recordings of respiration showed highly similar curves with both methods. The PVDF wire transducer seems to record the breathing movements at the level of the diaphragm with great reliability in EEG-polygraphy and it is inexpensive, easy to use and to clean.

This paper describes a simple method of event encoding as an extension to a previously defined standard format, the European Data Format (EDF). The specification ensures full backward compatibility with the existing definition. By using this extension, the format can be used to store both continuous recordings and selected epochs of recordings. The encoding is performed in a channel of event-codes or in a pseudo-channel for annotations. Standardisation of event encoding is discussed. Decoding of events or annotations from the extended format is implemented at the application level. Existing programs that do not support the new encoding scheme still operate correctly and can simply ignore the new channels in processing `extended' data files. The event encoding is also compatible with EDF's capability to encode channels of different sampling frequency.

Objectives: To design a warning system for the pediatric intensive care unit (PICU). The system should be able to make statements at regular intervals about the level of abnormality of the EEG. The warnings are aimed at alerting an expert that the EEG may be abnormal and needs to be examined. Methods: A total of 188 EEG sections lasting 6 h each were obtained from 74 patients in the PICU. Features were extracted from these EEGs, and with the use of fuzzy logic and neural networks, we designed an expert system capable of imitating a trained EEGer in providing an overall judgment of abnormality about the EEG. The 188 sections were used in training and testing the system using the rotation method, thus separating training and testing data. Results: The EEGer and the expert system classified the EEGs in 7 levels of abnormality. There was concordance between the two in 45% of cases. The expert system was within one abnormality level of the EEGer in 91% of cases and within two levels in 97%. Conclusions: We were able to design a system capable of providing reliably an assessment of the level of abnormality of a 6 h section of EEG. This system was validated with a large data set, and could prove useful as a warning device during long-term ICU monitoring to alert a neurophysiologist that an EEG requires attention.

Volume conductor models that are commonly used to describe the EEG and MEG neglect holes in the skull, lesions, the ventricles, and anisotropic conductivity of the skull. To determine the influence of these features, simulations were carried out using the finite element method. The simulations showed that a hole in the skull will have a large effect on the EEG, and as one of the consequences localisation errors up to 15 mm may occur. The effect on the MEG is negligible. The presence of a lesion may cause the shape and magnitude of the EEG and MEG to change. Hence, a lesion has to be taken into account, if the active neurones are close to it. Moreover, a localisation procedure may fail if the lesion is not included in the volume conductor model. Inclusion of the ventricles in the volume conductor model is necessary only if sources are in their vicinity or if their sizes are unusually large. Anisotropic conductivity of the skull has a smearing effect on the EEG but does not influence the MEG.

Optimal application of the nerve conduction study depends on an understanding of the principles and a recognition of the pitfalls of the technique. The conventional methods deal primarily with distal nerve segments in an extremity. Other techniques allow one to assess nerve segments in less accessible anatomical regions, to improve the accuracy in precisely localizing a focal lesion, and to increase the sensitivity in detecting subclinical abnormalities. Despite certain limitations, nerve conduction studies can provide diagnostically pertinent information if they are used judiciously in the appropriate clinical contexts.

This report describes the basic principle and examines the comparative accuracy of a novel method for locating 3-D coordinates of electrode positions on the head. The method involves calculation of the 3-D coordinates for any array of 10/10 electrode positions from 14 straight-line distances between 11 10/10 electrodes. In 11 subjects the 3-D coordinates of 64 scalp electrodes embedded in an electrode cap were identified with the novel method, and also with a standard commercial magnetic field digitizer. The outcomes from the two methods were compared with directly measured coordinates of all 64 positions (cf. De Munck, J.C., Vijn, P.C.M. and Spekreijse, H. A practical method for determining electrode positions on the head. Electroenceph. clin. Neurophysiol., 1991, 89: 85–87). Coordinates in 3 dimensions obtained using the new method were significantly closer to the directly measured values than those from the magnetic field digitizer. The new method was also quicker and requires less specialized instrumentation than the magnetic field digitization method. The novel method appears to be a valid and convenient tool for use with EEG analysis techniques that require specific information about 10/10 electrode positions.