Abstract
In the heart and brain coherent ionic currents flow across appreciable volumes producing detectable magnetic fields. In this paper I will survey other organs and processes which give rise to measurable fields. These are too diverse and numerous for the survey to be encyclopaedic: instead I will concentrate on those that have either attracted most attention or, in my view, seem most promising. They are:
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Contaminant magnetic material in the body The body may contain, as contaminants, ferromagnetic or ferrimagnetic material. Magnetite Fe3O4 is commonly found in dust and is easily inhaled. It is a strong ferrimagnet and as little as a fraction of a gram of magnetite in the lungs is easily detectable. By measuring the field outside the chest it is possible to both monitor the dust burden of the lungs and assess lung function. The measurements are entirely non-invasive.
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Intrinsic magnetic material in the body Overall, biological tissue is diamagnetic (with a susceptibility of order 10 −5 m−3) though, significantly, it does contain some paramagnetic material. In the Earth’s field; the presence of a biological organism changes the local magnetic induction by about 500 pT. SQUID magnetometers have sufficient sensitivity to map the local susceptibility variations of tissues as a way of probing their composition. This idea underlies a method of measuring stored iron levels in the liver.
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Quasi dc ionic currents Because of the difficulty of making reliable dc electrode measurements on biological systems, many potentially significant electrophysiological processes are unexplored. ‘Injury current’ is an example. This may be a simple epiphenomenon, but it has been suggested that the currents have a significant role in the repair process. A linked suggestion is that the ionic currents that accompany development help to ’shape’ the organism. DC magnetic field studies of such phenomena may allow monitoring of hidden injuries and help to elucidate fundamental biological processes.
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Swithenby, S.J. (1989). Biomagnetic Studies of Organs Other than the Heart and Brain. In: Williamson, S.J., Hoke, M., Stroink, G., Kotani, M. (eds) Advances in Biomagnetism. Springer, Boston, MA. https://doi.org/10.1007/978-1-4613-0581-1_5
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DOI: https://doi.org/10.1007/978-1-4613-0581-1_5
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