No abstract available

[en] 2-Mercaptoethylguanidine (MEG) enhances the hypotension reaction to bradykinine and kallidine injections. In normal and spinal rats the secondary rise of the blood pressure after bradykinine, caused by catecholamine liberation, was transformed into a hypotension through MEG. These effects are partially interpreted as sympatholytic effects of MEG. (orig.)

No abstract available

[en] An algorithm is described that localizes a set of simultaneously activated coils using MEG detectors. These coil positions are used for continuous or intermittent head position registration during long MEG sessions, to co-registrate MR and MEG data and to localize EEG electrodes attached to the scalp, when EEG and MEG are recorded simultaneously. The algorithm is based on a mathematical model in which the coils are described as stationary magnetic dipoles with known source time functions. This knowledge makes it possible to detect and remove bad channels automatically. It is also assumed that the source time functions are orthogonal. Therefore, the localization problem splits into independent localization problems, for each coil. The method is validated in a phantom experiment, where the relative coil positions were known. From this experiment it is found that the average error is 0.25 cm. An error of 0.23 cm was found in an experiment where 64 electrode positions were measured four times independently. Examples of the applications of the method are presented. Our method eliminates the use of an external 3D digitizer and maps the MEG directly onto other modalities. This is not only a practical advantage, but it also reduces the gross registration error. Furthermore, head motions can be monitored and MEG data can be corrected for these motions. (author)

[en] Standard methods for artefact removal in MEG or EEG measurements consist of rejection of either corrupted epochs or signal space projection (SSP). We propose to combine the two methods by applying SSP only in corrupted epochs and thus using both temporal and spatial information. This partial signal space projection necessarily results in smaller variances for the source localization. Formulae for dipole localization errors as a function of fraction of corrupted epochs are derived and verified in Monte Carlo simulations of MEG measurements corrupted with eye artefacts. A theoretical analysis of various measuring devices, classes of artefact and locations of dipole of interest shows that the proposed method leads to significant improvement for frontal signal dipoles and for 30-80% corrupted epochs. (author)

[en] Monitoring the electrical activity inside the human brain using electrical and magnetic field measurements requires a mathematical head model. Using this model the potential distribution in the head and magnetic fields outside the head are computed for a given source distribution. This is called the forward problem of the electro-magnetic source imaging. Accurate representation of the source distribution requires a realistic geometry and an accurate conductivity model. Deviation from the actual head is one of the reasons for the localization errors. In this study, the mathematical basis for the sensitivity of voltage and magnetic field measurements to perturbations from the actual conductivity model is investigated. Two mathematical expressions are derived relating the changes in the potentials and magnetic fields to conductivity perturbations. These equations show that measurements change due to secondary sources at the perturbation points. A finite element method (FEM) based formulation is developed for computing the sensitivity of measurements to tissue conductivities efficiently. The sensitivity matrices are calculated for both a concentric spheres model of the head and a realistic head model. The rows of the sensitivity matrix show that the sensitivity of a voltage measurement is greater to conductivity perturbations on the brain tissue in the vicinity of the dipole, the skull and the scalp beneath the electrodes. The sensitivity values for perturbations in the skull and brain conductivity are comparable and they are, in general, greater than the sensitivity for the scalp conductivity. The effects of the perturbations on the skull are more pronounced for shallow dipoles, whereas, for deep dipoles, the measurements are more sensitive to the conductivity of the brain tissue near the dipole. The magnetic measurements are found to be more sensitive to perturbations near the dipole location. The sensitivity to perturbations in the brain tissue is much greater when the primary source is tangential and it decreases as the dipole depth increases. The resultant linear system of equations can be used to update the initially assumed conductivity distribution for the head. They may be further exploited to image the conductivity distribution of the head from EEG and/or MEG measurements. This may be a fast and promising new imaging modality

[en] Radioprotective agents are first defined, and then a brief bibliography of relevant books, reviews and general discussions follows. The chemical names and formulae of radioprotective agents are listed with their accepted abbreviations and corresponding patented names. An historical introduction identifies four main steps in the development of knowledge of chemical protection against ionizing radiations. Possible mechanisms of the radioprotective behaviour of different compounds are discussed. A table of sulphur-containing compounds with dose (mg/kg) and any radioprotective effect in various mammals identifies a common structural feature of the most active protective agents as a two or three carbon chain with a strong basic group (amino or guanidino) at one end and a thiol at the other. These compounds have chelating properties. The significance of the intramolecular transguanylation of AET to MEG (mercaptoethylguanidine) in phosphate buffer is emphasised. It is suggested that the sulphur-containing radioprotective substances should be considered as a particular class of drugs, since they exhibit peculiar, rapid transient toxic effects in mammals at the dose required for radioprotective action. (U.K.)

No abstract available

[en] The assay for potency was carried out by use of 35 kinds of sulfur containing compounds in order to investigate useful protective drugs for the relief of skin injury caused by irradiation and to elucidate the relationship between their chemical structures and potency manifestation. The protective potency was determined after the irradiation of 1200 R on mice by use of 30 kVp of soft X-ray. In derivatives such as cysteamine, cysteine, thiourea, and isothiourea, a strong protective potency was observed and this potency was enhanced in compounds on which SH-groups are released or apt to be released from a chemical structural point of view. In dithiocarbamates, protective potency was also detected. (author)

[en] The cytoplasm of normal and tumorous rat liver cells contains a heat-resistant compound with reducing ability to break the mixed disulfide bond of albumin-¹⁴C-mercaptoethylguanidine. The reducing activity of cytosol is destoryed by 1000 krd ⁶⁰Co-gamma-ray doses in diluted solution. In vivo supralethal of rats does not affect the activity of cytosol prepared from liver cells. (orig.)