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Biomedical subjects

C Kornhuber

Publications and source records attributed to C Kornhuber.

5 recordsLinked to original sources
PubMed1993

First experiences with a multichannel software gradiometer recording normal and tangential components of MEG.

We describe a 28-channel magnetometer that operates as a 22-channel 'software gradiometer'. Gradiometer function is achieved by subtraction of weighted signals representing the noise field along three orthogonal axes as detected by six compensation channels. The instrument measures both normal and tangential field components; the user can select a total of 22 normal and/or tangential measuring sites from two arrays of 16 sites each. First experiences indicate that the combination of a shielded room with a software suppression of the residual field entering the room is amply sufficient to allow biomagnetic measurements in a hospital environment.

Brain Mapping↗
PubMed1991

Stability of human blood serum aminoacids after storage at different pH and temperature conditions.

The stability of the aminoacids in human blood serum ultrafiltrates and in an aminoacid standard solution was investigated under different pH and storage conditions. At close to neutral pH values the aminoacid concentrations remained constant for at least 12 months at -50 degrees C (n = 6), except for lysine. With acid but particularly with alkaline conditions a time- and temperature-dependent decrease was observed for glutamine and asparagine with concomitant increases of glutamate and aspartate. Similar, but less prominent alterations were noted for the concentrations of methionine, glycine, tyrosine, histidine, arginine and ornithine. Almost independent of pH, there was an effect of temperature; after 24 h at 55 degrees C a significant increase of several per cent in a number of serum aminoacid concentrations was observed, presumably due to the hydrolysis of small proteins and peptides. For the purpose of aminoacid analysis it is recommended that samples be stored deproteinized, deep-frozen and at neutral pH.

Adult↗
PubMed1991

A comparison of normal and tangential magnetic field component measurements in biomagnetic investigations.

Because of the way most available hardware gradiometers are designed and in view of the prediction, by theory, that the normal magnetic field component provides all available information on the intrinsic current source, MEG and MCG measurements generally consider only the field vector normal to the head or truck surface. However, when looking for single events, the information contained in the normal component often cannot be fully sampled, because the sensor array has limited dimensions and therefore covers only a fraction of the field's spatial extension. Simulation of a current dipole in a sphere using realistic parameters shows that there is a considerable area where the amplitude of the tangential field components is larger than that of the normal one. Measurements using a 28-channel magnetometer system with normal and tangential pick-up coils and a current dipole in a phantom model confirm this prediction; depending on dipole orientation, the signal-to-noise ratio (SNR) could improve by a factor of up to 20 if the total field was considered instead of only the normal component. MCG recordings with the same instrument demonstrated a broad area above the heart where the tangential SNR was clearly better than the normal one. Preliminary measurements indicate that tangential components can also be recorded in the MEG; it is suggested that they may help source localisation.

Brain↗