56 research outputs found
Magnetic stimulation for non-homogeneous biological structures
BACKGROUND: Magnetic stimulation has gained relatively wide application in studying nervous system structures. This technology has the advantage of reduced excitation of sensory nerve endings, and hence results in quasi-painless action. It has become clinically accepted modality for brain stimulation. However, theoretical and practical solutions for assessment of induced current distribution need more detailed and accurate consideration. Some possible analyses are proposed for distribution of the current induced from excitation current contours of different shape and disposition. Relatively non-difficult solutions are shown, applicable for two- and three-dimensional analysis. METHODS: The boundary conditions for field analysis by the internal Dirichlet problem are introduced, based on the vector potential field excited by external current coils. The feedback from the induced eddy currents is neglected. Finite element modeling is applied for obtaining the electromagnetic fields distribution in a non-homogeneous domain. RESULTS: The distributions were obtained in a non-homogeneous structure comprised of homogeneous layers. A tendency was found of the induced currents to follow paths in lower resistivity layers, deviating from the expected theoretical course for a homogeneous domain. Current density concentrations occur at the boundary between layers, suggesting the possibility for focusing on, or predicting of, a zone of stimulation. CONCLUSION: The theoretical basis and simplified approach for generation of 3D FEM networks for magnetic stimulation analysis are presented, applicable in non-homogeneous and non-linear media. The inconveniences of introducing external excitation currents are avoided. Thus, the possibilities are improved for analysis of distributions induced by time-varying currents from contours of various geometry and position with respect to the medium
Systematic assessment of training-induced changes in corticospinal output to hand using frameless stereotaxic transcranial magnetic stimulation.
Measuring changes in the characteristics of corticospinal output has become a critical part of assessing the impact of motor experience on cortical organization in both the intact and injured human brain. In this protocol we describe a method for systematically assessing training-induced changes in corticospinal output that integrates volumetric anatomical MRI with transcranial magnetic stimulation (TMS). A TMS coil is sited to a target grid superimposed onto a 3D MRI of cortex using a stereotaxic neuronavigation system. Subjects are then required to exercise the first dorsal interosseus (FDI) muscle on two different tasks for a total of 30 min. The protocol allows for reliably and repeatedly detecting changes in corticospinal output to FDI muscle in response to brief periods of motor training
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Use of nuclear explosives for excavation of a sea-level canal across the Negev Desert in Israel, connecting the Mediterranean with the Gulf of Aqaba
Another interesting application of nuclear excavation would be a sea- level canal 160 miles long across Israel, connecting the Mediterranean with the Gulf of Aqaba (and thus the Red Sea and the Indian Ocean). Such a canal would be a strategically valuable alternate to the present Suez Canal and would probably contribute greatly to the economic development of the surrounding area. The difference in elevation between sea level and the Dead Sea (30 miles away and 1286 feet below sea level) might also be used to generate hydroelectric power. The maximum depth of excavation to be encountered is on the order of 1500 feet. Conventional methods of excavation of this magnitude are prohibitively expensive, if indeed possible, but it appears that nuclear explosives could be profitably applied to this situation
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Composition of High-Energy Heavy-Ion Beams: Preliminary Measurements
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Fluctuations of energy loss by heavy charged particles in matter
Bone changes after maxillary sinus surgery: an experimental scanning electron microscopy study
Interaction of MRI field gradients with the human body
In this review, the effects of low-frequency electromagnetic fields encountered specifically during magnetic resonance imaging (MRI) are examined. The
primary biological effect at frequencies of between 100 and 5000 Hz (typical of MRI magnetic field gradient switching) is peripheral nerve stimulation, the result of which can be a mild tingling and muscle twitching to a sensation of
pain. The models for nerve stimulation and how they are related to the rate of change of magnetic field are examined. The experimental measurements, and analytic and computational modelling work in this area are reviewed. The
review concludes with a discussion of current regulation in this area and current practice as both are applied to MRI
Direct injection of noise to the visual cortex decreases accuracy but increases decision confidence
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