Partial independence of bioelectric and biomagnetic fields and its implications for encephalography and cardiography
| Autor: | Andrei Irimia, Kenneth R. Swinney, John P. Wikswo |
|---|---|
| Rok vydání: | 2009 |
| Předmět: |
Electromagnetic field
Physics Electroencephalography Models Biological Article Magnetic field Electrocardiography Dipole Electromagnetic Fields Nuclear magnetic resonance Heart Conduction System Quantum electrodynamics Quadrupole Animals Humans Computer Simulation Electric potential Magnetic potential Nerve Net Multipole expansion Magnetic dipole |
| Zdroj: | Physical Review E. 79 |
| ISSN: | 1550-2376 1539-3755 |
| DOI: | 10.1103/physreve.79.051908 |
| Popis: | In this article, we clearly demonstrate that the electric potential and the magnetic field can contain different information about current sources in three-dimensional conducting media. Expressions for the magnetic fields of electric dipole and quadrupole current sources immersed in an infinite conducting medium are derived, and it is shown that two different point dipole distributions that are electrically equivalent have different magnetic fields. Although measurements of the electric potential are not sufficient to determine uniquely the characteristics of a quadrupolar source, the radial component of the magnetic field can supply the additional information needed to resolve these ambiguities and to determine uniquely the configuration of dipoles required to specify the electric quadrupoles. We demonstrate how the process can be extended to even higher order terms in an electrically silent series of magnetic multipoles. In the context of a spherical brain source model, it has been mathematically demonstrated that the part of the neuronal current generating the electric potential lives in the orthogonal complement of the part of the current generating the magnetic potential. This implies a mathematical relationship of complementarity between electroencephalography (EEG) and magnetoencephalography (MEG), although the theoretical result in question does not apply to the non-spherical case (Dassios (2008), Math Med Biol, vol. 25, p. 133). Our results have important practical applications in cases where electrically silent sources that generate measurable magnetic fields are of interest. Moreover, electrically silent, magnetically active moments of higher order can be useful when cancellation due to superposition of fields can occur, since this situation leads to a substantial reduction in the measurable amplitude of the signal. In this context, information derived from magnetic recordings of electrically silent, magnetically active multipoles can supplement electrical recordings for the purpose of studying the physiology of the brain. Magnetic fields of the electric multipole sources in a conducting medium surrounded by an insulating spherical shell are also presented and the relevance of this calculation to cardiographic and encephalographic experimentation is discussed. |
| Databáze: | OpenAIRE |
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