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Biomedical subjects

H Nowak

Publications and source records attributed to H Nowak.

At least 55 records · Page 3Linked to original sources
PubMed1997

Abnormalities of auditory evoked magnetic fields and structural changes in the left hemisphere of male schizophrenics--a magnetoencephalographic-magnetic resonance imaging study.

Functional and structural changes in 10 DSM-III-R male schizophrenics and 10 healthy volunteers were investigated using magnetoencephalographically (MEG) detected long-latency (N100 m) auditory evoked fields (AEFs) and magnetic resonance imaging (MRI). The AEFs were characterized by single moving equivalent dipoles, which were superimposed on MRIs. There were significant differences in dipole orientations and in AEF latencies in the left hemisphere of schizophrenics, when compared to the controls. The MEG-detected alterations were found to be associated with a bilateral volume reduction of the posterior superior temporal gyrus (pSTG), which was more pronounced in the left hemisphere. Separate analysis of white and gray matter has shown that the pSTG volume reduction resulted from decreased gray matter volumes without white matter changes. Both the functional and the morphological data indicate a left-hemispheric disturbance in our patients.

Adult↗
PubMed1997

Influence of tissue resistivities on neuromagnetic fields and electric potentials studied with a finite element model of the head.

Modeling in magnetoencephalography (MEG) and electroencephalography (EEG) requires knowledge of the in vivo tissue resistivities of the head. The aim of this paper is to examine the influence of tissue resistivity changes on the neuromagnetic field and the electric scalp potential. A high-resolution finite element method (FEM) model (452,162 elements, 2-mm resolution) of the human head with 13 different tissue types is employed for this purpose. Our main finding was that the magnetic fields are sensitive to changes in the tissue resistivity in the vicinity of the source. In comparison, the electric surface potentials are sensitive to changes in the tissue resistivity in the vicinity of the source and in the vicinity of the position of the electrodes. The magnitude (strength) of magnetic fields and electric surface potentials is strongly influenced by tissue resistivity changes, while the topography is not as strongly influenced. Therefore, an accurate modeling of magnetic field and electric potential strength requires accurate knowledge of tissue resistivities, while for source localization procedures this knowledge might not be a necessity.

Adipose Tissue↗
PubMed1997

[Effect of boundary element discretization on forward calculation and the inverse problem in electroencephalography and magnetoencephalography].

Modelling in magnetoencephalography (MEG) and electroencephalography (EEG) is increasingly based on the boundary element method (BEM). We quantify the influence of boundary element discretization on the neuromagnetic and neuroelectric forward and inverse problem for different dipole depths, brain regions and the quasispherical correction. In particular we derive standards for the general use of BEM models in MEG/EEG source localization. For this purpose simulation with single current dipoles, and source reconstructions from somatosensory evoked potentials and magnetic fields were employed. It was found that both local and global discretization influence source reconstruction. Only at a minimum triangle side length of 10 mm was it possible to achieve stable results for MEG and EEG. In order to obtain acceptable errors within the stable region, the ratio of dipole depth to triangle side length must not be less than 0.5. The results obtained from a comparison of the different brain regions indicate that the similarity to spherical geometry might well have an influence on the estimated dipole location, but not so much on its strength. Source reconstruction employing quasispherical correction was found to be the most stable, in particular in the case of coarse BEM discretization.

Adult↗
PubMed1997

Reliability of dipole localization for the movement-evoked field component MEF I.

The movement-evoked field I (MEF I) component is the largest and most stable neuromagnetic component accompanying self-paced movements. In order to use MEG for studying dynamic changes in the cortical organization of movements, data about the reliability and variability of these neuromagnetic components for individual subjects must be established during different sessions. For this aim, three male subjects were requested to perform self-paced flexions of their index finger and thumb in repeated sessions while the MEG was recorded by a 31 channel system. The MEF I was identified for each session and a single equivalent dipole was calculated for this component. The dipole localizations of the various sessions were compared. The standard deviation of the localization for all persons and all values amounts to 4.0-5.2 mm for the three spatial dimensions. Our data suggest that the spatial distance between two single focal sources fitted to the MEF I must be greater than 14 mm to be interpreted as distinct. However, the neuromagnetic field structure and the resulting dipole localization of the MEF I component are quite stable and could be used for the evaluation of cortical plasticity.

Adult↗
PubMed1996

Internal consistency of dipole localizations for the human movement-evoked magnetic field component 1 (MEF 1).

The present magnetoencephalographic study was conducted in order to assess the accuracy of dipole localizations for the movement-evoked field component 1 (MEF 1). Three male subjects were requested to perform self-paced flexions of their index finger and thumb in repeated sessions of 60 trials while the neuromagnetic field was recorded by a 31 channel system. Single moving dipole localizations were performed for the MEF 1. The error within single sessions was calculated by split-half reliability and window-homogeneity in a total of 61 sessions. The mean spatial deviation between both halves amounted to 3.8 mm. The window-homogeneity was found to be 2 mm deviation/10 ms.

Adult↗
PubMed1995

[Dealing with adverse effects in phase I trials].

A questionnaire was completed by members of the Association for Applied Human Pharmacology (AGAH) in Germany with the aim of assessing the present situation regarding management of adverse events (AEs). A recommendation for documentation and evaluation of AEs was to be presented after discussion within the AGAH. The questionnaire referred to general questions, documentation of AEs, intensity and causality, coding and serious adverse events (SAE). Percentage return of answered questionnaires was 54.5%. Of the people contacted, 9.1% said they did not carry out phase I trials, and 36.4% did not reply. The survey in the 24 institutes convers an estimated 11200 volunteers who are included in clinical trials each year. The discussion about commencement of AEs documentation and its duration was contentious. Of the respondents, 38.5% AEs only after application of the trial substance, while 61.5% also make a documentation during the pre-trial phase (recruitment, pre-examination, supervision before application). 13.6% document only up to the post-examination and half of those questioned until AE symptoms have disappeared. 22.7% document until disappearance of symptoms only when AEs are definitely associated with the trial substance. A 3-point scale is used by most people questioned for evaluation of the intensity of an AE. Evaluation of causality, mostly undertaken by the examining physician and the director of the clinical trial, is not carried out homogeneously. There are several categories, but four classifications are most commonly used. 62.5% of codings of AEs are carried out according to the WHO Adverse Reaction Terminology.(ABSTRACT TRUNCATED AT 250 WORDS)

Adverse Drug Reaction Reporting Systems↗
PubMed1991

Multichannel magnetography in unshielded environments.

Any biomagnetic instrumentation requires a very sensitive sensor. As the strength of the magnetic field of interest ranges from about 10 fT to 50 pT, the only field sensor having the required sensitivity and small sampling volume is the superconducting quantum interference device (SQUID) e.g. thin-film DC SQUIDs. For transforming the signal from the antenna to the SQUID, a thin-film coupling coil is used. The SQUID itself is shielded and therefore insensitive to external noise. In a five-channel system second-order gradiometers are used in an unshielded environment. The measuring system enables us to balance each channel by means of lead plates without removing it from liquid helium. The lead plates can be handled by a revolver system from outside the dewar. By an iterative balancing procedure inside an artificial uniform field, imbalances less than 10(-4) could be achieved. These results are confirmed by mathematical calculation of mechanical balancing. Sensitivities down to 20 fT Hz-1/2 could be achieved during 'quiet' hours. Another method for the suppression of disturbances is electronic balancing. One of the most important problems in the multichannel system is the cross talk between the single channels. With respect to the geometry of our five-channel device the cross talk coefficient was calculated to be 3.9% and measured at 3.8%.

Equipment Design↗
PubMed1991

[Effect of vibration on crystalline lens transparency].

It was demonstrated experimentally that the transparency of the eye lenses diminishes under the influence of a prolonged vibration. Investigations were performed in a group of rabbits which were subjected to a long-lasting exposition to mechanical vibration of 10 Hz throughout a period of 5 months. The transparency of the extracted lenses was evaluated by spectrophotometry and compared with lenses of 2 control groups. Group 1 consisted of rabbits which in the same period of 5 months were subjected to a continuous neon illumination of 1200 lx intensity as a cataractogenous factor. A second comparative group consisted of rabbits not exposed to any external factor. The authors detected a statistically significant decrease of transparency of lenses of the examined group in reference towards the second comparative group, it was however smaller than in the 1-st group.

Absorption↗