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J Vieth

Publications and source records attributed to J Vieth.

At least 37 records · Page 2Linked to original sources
PubMed1993

[Functional imaging of the brain. Magnetoencephalography (MEG)].

Magnetencephalography (MEG) is a new diagnostic tool for the exact localization of the biomagnetic sources of the electrical activity of the brain. The extremely weak magnetic fields are generated by the postsynaptic activity of the neurons, acting like current dipoles. They are measured with a SQUID (superconducting quantum interference device). Only the tangential components of the dipoles contribute to the measurable field outside the head. For MEG localization of sources, the brain is modelled as a sphere of homogeneous electrical conductivity, the center of which is fitted to MR images of the head. As a model of the current sources a one- or two-dipole model is used. For the analysis of more complex sources, however, a principle component analysis (PCA) should be performed before the dipole analysis, or the current-density distribution should be used. The effect of background activity can be eliminated by alpha wave filtering and the dipole-density plot (DDP), which also increases the signal/noise ratio. MEG seems to be useful in purely functional lesions of the brain. A final decision on the value of MEG for routine diagnosis is not yet possible, however.

Brain↗
PubMed1992

Functional 3D localization of cerebrovascular accidents by magnetoencephalography (MEG).

Spontaneous magnetic slow wave brain activity can be used to locate the underlying sources with sufficient accuracy by using the single current dipole model. To locate focal sources from spontaneous activity a tool had to be developed to extract focal densities of dipoles across time-the dipole density plot. The first version works on discrete volume units and is used for screening. The second version avoids a possible localization error and works continuously and this even is done on individual slices. The DDP seems to be a valuable tool for extracting and separating different focal sources from the background activity. Not only brain infarctions and haemorrhages (and cysts and angiomas) could be located, but also functional sources associated with TIAs even one week after the symptoms. First results let us assume that clinically silent TIAs also (in analogy to clinically silent brain infarctions) could be detected and located.

Brain↗
PubMed1991

Magnetic fields of the brain analysed by a multiple dipole approach using factor analysis.

Sudden spatial changes in consecutive dipole localisations suggest that often a single-moving-dipole algorithm is inadequate. This is particularly important in the case of widespread activity in the brain, where one extremum may be extinguished by another. One example of widespread activity is the alpha rhythm. The application of factor analysis may give information about the presence of different active sources. The alpha rhythm showed two to three significant factors. This suggests that the apparent movement suggested by single-dipole localisation may be caused by the superposition of the fields of two spatially and temporally distinct sources. Field maps which are very similar to a dipole pattern may be caused by a superposition of the fields of several sources.

Brain↗
PubMed1990

State of the multichannel magnetoencephalography.

It could be demonstrated in many investigations with single- or several- channel magnetic recording instruments that, a focal pathological source could be located mainly in close connection to verified brain lesions. Our experience with a 37- channel instrument did support these results. In addition, we had available the whole dynamics of the brain activity in time and space, but it must be considered, that the pathological activity is mixed more or less with the background activity. One simple method to separate partly both activities is the "dipole density plot" (DDP), which concentrates the density of dipoles in areas of focal pathological activity.

Brain↗
PubMed1986

Vigilance, sleep and epilepsy.

The correlations between vigilance and epilepsy are manifold. Nearly all epileptic seizures cause a diminution of vigilance extending to unconsciousness. Many of the influences triggering or inhibiting epileptic seizures produce alterations of vigilance or are produced by them. Nearly all chemical influences more or less cause diminution of vigilance. The enhancement of vigilance may inhibit seizures. Decreasing vigilance may act vice versa. As a means to enhance vigilance afferent stimuli are able to trigger seizures. This may be accomplished when singular or rhythmic stimulation of afferents gets the already excited neuronal system oscillating. This principle is also responsible for the strong correlation between triggering of seizures and the sleep/waking cycle with its different grades of neuronal synchronization. On the other hand, inhibition of seizures is possible by a continuously applied stimulation load, which may disturb the increasing excitatory oscillation. Also, conditioning may trigger or inhibit seizures. But the EEG biofeedback only is used to decrease abnormal neuronal activity.

Arousal↗
PubMed1984

[Magnetoencephalography, a new function diagnostic method].

Recording of MEG is possible by the existence of magnetic fields caused by flowing electric currents. The magnetic field produced by neurons is at least one million times weaker than the steady earth field or other disturbing fields. The application and the current development of the SQUID technology operating by superconduction makes registration possible even in an unshielded envirement. The MEG has the following advantages compared with the EEG: The MEG has no artifacts of electrodes and eye movements as the EEG does. Reference electrodes are not needed thus no artifacts of these occur. Therefore recording of the steady magnetic field of the brain can be done. The localization of neuronal sources is more distinct and circumscript in the MEG than in the EEG. For several reasons not all components of the MEG are found in the EEG and vice versa. MEG and EEG is a meaningful combination. The MEG allows also to record and localize sources in the deep of the brain, i.e. beneath the cortex. A three dimensional functional realtime measurement is possible. In the future the MEG technique allows a lot of possibilities not only in the research but also in the dayly functional diagnosis.

Arousal↗