[Weighted averaging of weak neuronal magnetic fields with reference to covariance of strong noise components].
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Afferent Pathways↗
Biomedical subjects
L Trahms
Publications and source records attributed to L Trahms.
Magnetometry of evoked fields from human peripheral nerve, brachial plexus and primary somatosensory cortex using a liquid nitrogen cooled superconducting quantum interference device.
Superconducting Quantum Interference Devices (SQUIDs) can be used to detect neuromagnetic fields evoked in the peripheral and central nervous system. Up to now, such measurements had to be based on SQUIDs with a low critical temperature (Tc) requiring liquid helium cooling. Recent improvements in high-Tc SQUID technology relying on liquid nitrogen cooling led to a significant reduction in the system's noise level. Hare, first high-Tc recordings of weak neuromagnetic fields are demonstrated. In particular, along the entire somatosensory afferent pathway including peripheral nerves, brachial plexus and primary somatosensory neocortex evoked neuromagnetic activities were detected using conventional recording parameters for bandwidth and number of averages. This opens up a wide perspective for cost-effective high-Tc magnetometry in clinical neuroscience.
Brachial Plexus↗
Magnetic markers as a noninvasive tool to monitor gastrointestinal transit.
A novel method to monitor gastrointestinal transit of solid oral dosage forms or nutrients is presented, providing a simultaneous recording of gastrointestinal motility of the traversed section. Based on the measurement of the magnetic field of an ingested magnetized marker, its location is found by fitting a magnetic dipole field to the measured data.
Gastrointestinal Motility↗
Multichannel magnetic recording of P300 activity.
The magnetic correlate of the P300 wave was registered using a seven-channel detector. The spatial variation of the corresponding field suggests the contribution of outer brain layers to the neural activity of M300.
Brain↗
Nerve, plexus and spinal cord: possible targets for non-invasive neuromagnetic measurements in man.
Somatosensory evoked neuromagnetic fields are recorded from peripheral nerves in the upper arm, from plexus brachialis at the ventral and dorsal thorax and from the dorsal horn of the cervical spinal cord ('P13m') at the upper lateral neck. Some perspectives for clinical applications are suggested.
Brachial Plexus↗
Exploratory mapping of evoked neuromagnetic activity from human peripheral nerve, brachial plexus and spinal cord.
Upon conventional median nerve stimulation at the wrist early magnetic fields were recorded using a SQUID magnetometer. At the upper arm, mono- and biphasic compound nerve action fields were detected, depending on the subject's distribution of single fiber conduction velocities. At the upper thorax, brachial plexus fields reversed polarity at the level of Erb's point; their distribution was asymmetric, probably due to volume currents. At the upper lateral neck, fields from proximal plexus, spinal cord (P13m) and the primary somatosensory cortex contralateral to the sensor position were detected. The observed P13m field distribution agrees with the electrophysiological concept of a sagittal segmental dorsal horn generator.
Brachial Plexus↗
Multipole expansions in the representation of current sources.
After obtaining the measured magnetic field or its components in the form of an isofield map one has to decide which approximation to use in solving the inverse problem. A single current dipole as an equivalent current source is often used. It will be shown when this approximation fails and one possible way to improve the equivalent source description. The expansion of current multipoles is discussed up to the second order. The localization of an equivalent current source in this case is considered. The application of this type of expansion is analysed and discussed.
Bioelectric Energy Sources↗
[The "magnetospinogram"--a step toward functional localization of evoked spinal cord activity].
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Afferent Pathways↗
[Magnetic markers in the gastrointestinal tract--a new method for the study of absorption of solid oral drugs].
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Administration, Oral↗
Biomagnetic functional localization of a peripheral nerve in man.
The first detection of the magnetic field of a stimulated peripheral nerve in man is presented. The measurement was performed noninvasively and in vivo on a healthy subject. The spatio-temporal field distribution is utilized to calculate the location of bioelectric activity on the basis of the equivalent current dipole model. The localization of the active nerve tissue is confirmed by a computer tomography image of the upper arm cross-section. Furthermore, a calculation of the total current distribution in the nerve explains the observed morphology of the signal.
Electric Stimulation↗
A 1H and 13C NMR study of motional changes of dipalmitoyl lecithin associated with the pretransition.
Motional changes of the dipalmitoyl lecithin molecule associated with the pretransition in multibilayers are investigated by proton-enhanced 13C-NMR and proton spin-locking experiments. The nitrogen-bound methyl groups of the polar head exhibit faster motion and more disorder in the intermediate phase compared with the gel phase. Although little or no change occurs in the hydrocarbon chain order at the pretransition, the corresponding motional correlation time changes by one order of magnitude. This is consistent with a model involving rotational motion of the hydrocarbon chains about their long axes: in the gel phase the motion is such that neighboring chains make an oscillating disrotatory motion, while in contrast, in the intermediate phase a quasi-free chain rotation takes place. Earlier contradicting results of Davies, J., 1979, Biophys. J., 27:339-358, and ourselves, Trahms, L., and E. Boroske, 1979, Biochim, Biophys. Acta. 552:189-193, are explained by this model.
Kinetics↗
1H-NMR study of the three low temperature phases of DPPC-water systems.
The three phases of dipalmitoylphosphatidylcholine-water dispersions, occurring below the main transition are studied by a moment analysis of 1H-nuclear magnetic resonance (NMR) spectra. The subtransition, recently detected by Chen, S. C., J. M. Sturtevant, and B. J. Gaffney, 1980, Pro. Natl. Acad. Sci. USA, 77:5060-5063, is characterized by a sharp drop in the second moment at 12 degrees C as a result of increasing the temperature. Interesting features of this phase transition are a hysteresis of 11 K and extremely slow kinetics. It is interpreted as the onset of a flip-flop of the hydrocarbon chains about their long axis. At the pretransition, this type of motion is assumed to change into a fast rotation. The proposed models for the three phases are confirmed by computer calculations of theoretical values for the second and fourth moments of the corresponding NMR signals.
Kinetics↗
The distinction of corneal water in free and bound fractions.
The corneal water is studied by NMR measurements. There are two fractions of water, one more strongly bound to relaxation centres of proteoglycanes and the other almost freely diffusible as liquid bulk water. A quantitative analysis shows that the bound fraction makes up a very small part (less than 1%) of the total water. So nearly all the water is available for the nutrition of the cornea by diffusion.
Collagen↗
Pulse NMR study of phase transitions in dipalmitoyl phosphatidylcholine multilayer systems.
Pretransition and main transition of aqueous dipalmitoyl phosphatidylcholine (DPPC) dispersions were investigated by pulse NMR. The second moment M2 inter of the proton absorption line shows significant changes at 42 degrees C and about 35 degree C. Over the whole investigated temperature range between 25 and 50 degree C a superposition of at least two distinct second moments assigned to different molecular regions was observed.
Magnetic Resonance Spectroscopy↗
Quantification of magnetic nanoparticles by magnetorelaxometry and comparison to histology after magnetic drug targeting.
Magnetic nanoparticles can be used in medicine in vivo as contrast agents and as a drug carrier system for chemotherapeutics. Thus local cancer therapy is performed with Magnetic Drug Targeting (MDT) and allows a specific delivery of therapeutic agents to desired targets, i.e., tumors, by using a chemotherapeutic substance bound to magnetic nanoparticles and focused with an external magnetic field to the tumor after intraarterial application. Important for this therapeutic principle is the distribution of the particles in the whole organism and especially in the tumor. Therefore we used magnetorelaxometry to quantify ferrofluids delivered after MDT. Tissue samples of some mm3 volume of a VX2 squamous cell carcinoma were measured by magnetic relaxation and the amount of iron was determined using the original ferrofluid suspension as a reference. From this the distribution of the magnetic particles within the slice of tumor was reconstructed. Histological cross-sections of the respective tumor offer the opportunity to map quantitatively the particle distribution and the vascularisation in the targeted tumor on a microscopic scale. Our data show that the integral method magnetorelaxometry and microscopic histological methods can complete each other efficiently.
Animals↗