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Measurement of Electrical Potentials and Magnetic Fields from the Body Surface
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
All biomagnetic measurements are based on the physical principle that moving charges generate a magnetic field. Classical mathematical derivations of the magnetic field intensity generally assume some constant current, I, flowing in a long, straight wire. Current is simply the number of charges/s passing a plane though the wire's cross-sectional area. In metal wires, current is carried by mobile conduction band electrons. In biological systems, there are no wires, and current is best thought of as current density, J(ρ,θ,ϕ), in amps/m2, in spherical coordinates. Current density is a vector quantity whose direction is the same as the velocity of the ⊕ ions drifting in an electric field and/or responding to a concentration gradient by movement from high to low concentration volumes. Current density is also related to the electric field distribution in the volume conductor: J = σE, where σ is the effective conductivity of the biological medium (e.g., the brain). In biological tissues, conductivity is also a function of position, that is, σ(ρ,θ,ϕ) S/m.
Introduction
Published in Shoogo Ueno, Tsukasa Shigemitsu, Bioelectromagnetism, 2022
Shoogo Ueno, Tsukasa Shigemitsu
Biomagnetism is the study of magnetic fields originating from biological systems. It also deals with magnetic phenomena of biological systems, which can be observed at different intensities and frequencies. For example, the so-called magnetophosphene is a visual sensation caused by exposing the head to a low-frequency (around 10–70 Hz) magnetic field of around 10–20 mT. This sensation is generated in the retina. The earliest magnetic stimulation was reported by Jacques-Arsene d’Arsonval. Magnetic stimulation is based on Faraday’s law of induction. This law states how the change of an applied magnetic field induces an electric field with accompanying current in the tissue. The first magnetic stimulation of nerve was described by Alexander Kolin in 1959. Magnetic stimulation of the human brain and heart has been used for the purpose of both research and clinical treatment. The biological magnetic fields are extremely weak compared to the geomagnetic fields. The biological magnetic field of the human heart, called magnetocardiogram (MCG), was first detected by Gerhard Baule and Richard McFee in 1963. The biological magnetic field of the human brain called magnetoencephalogram (MEG) was detected by David Cohen in 1968. After these pioneering studies, using superconductive quantum interference devices techniques, the weak biological magnetic fields from the brain, heart and lung were easily measured from outside the body. Biomedical stimulation with ELF electric or magnetic fields was used first for clinical applications such as the healing of bone fracture. Fundamental research activities have been carried out for the healing promotion of various tissues. However, there is still no widely accepted mechanism by which ELF electric or magnetic fields can affect biological tissues. The well-known interaction between ELF electric or magnetic fields and biological tissues is the eddy currents induced in the tissues, which is a possible candidate mechanism. The other candidate is the interaction of the applied magnetic fields with an endogenous magnet such as magnetite. Because the brain is so important for human behavior, and because the functions of the brain inherently involve a great amount of electrical activity, since the beginning of bioelectromagnetism, it has been essential to examine the effects of magnetic fields, electric fields and currents, since they can induce electric fields and currents on the brain.
Developments in the human machine interface technologies and their applications: a review
Published in Journal of Medical Engineering & Technology, 2021
Harpreet Pal Singh, Parlad Kumar
Biomagnetism is a phenomenon by which the magnetic fields are produced by virtue of electrical currents generated by different body organs and magnetic properties of the constituent body materials. The magnetocardiogram (MCG) and magnetoencephalogram (MEG) are the two types of biomagnetic signals which are emerged by the functional activity of the heart and brain respectively [140]. Assessment of bio-impedance signals is a widely used approach in the monitoring and analysis of the health status of the human body by evaluating the electrical attributes of the biological tissues. The various methods are being utilised using bio-impedance signals based on the commonly used prediction equations in clinical diagnostics to assess the composition of the human body and prognosis of different body organs [141].
Spinal dura mater: biophysical characteristics relevant to medical device development
Published in Journal of Medical Engineering & Technology, 2018
Sean J. Nagel, Chandan G. Reddy, Leonardo A. Frizon, Matthieu K. Chardon, Marshall Holland, Andre G. Machado, George T. Gillies, Matthew A. Howard, Saul Wilson
The biomagnetic characteristics of the body have long been investigated and understood within the context of MR imaging. Schenck’s early, thorough review [26] of the role of magnetic susceptibility, χ, in medical imaging provides a wealth of detail on the topic. The values of χ for the various soft tissues are typically taken to be that of water at body temperature, χ ≈ −9 × 10−6, since the available in vivo data cluster around that slightly diamagnetic value. As a practical matter, we include dura mater in that category and note that whatever residual susceptibility it has is such that paramagnetic contrast agents must be taken up within it in order for magnetic resonance imaging to resolve certain kinds of localised anomalies in thickness [27,28].
Light, the universe and everything – 12 Herculean tasks for quantum cowboys and black diamond skiers
Published in Journal of Modern Optics, 2018
Girish Agarwal, Roland E. Allen, Iva Bezděková, Robert W. Boyd, Goong Chen, Ronald Hanson, Dean L. Hawthorne, Philip Hemmer, Moochan B. Kim, Olga Kocharovskaya, David M. Lee, Sebastian K. Lidström, Suzy Lidström, Harald Losert, Helmut Maier, John W. Neuberger, Miles J. Padgett, Mark Raizen, Surjeet Rajendran, Ernst Rasel, Wolfgang P. Schleich, Marlan O. Scully, Gavriil Shchedrin, Gennady Shvets, Alexei V. Sokolov, Anatoly Svidzinsky, Ronald L. Walsworth, Rainer Weiss, Frank Wilczek, Alan E. Willner, Eli Yablonovitch, Nikolay Zheludev
Ronald Walsworth then provides a very detailed and stimulating description of the wide-ranging applications (already achieved or envisioned) for diamond NV colour centres as precision quantum sensors in both the physical and life sciences. They have already been used to study important aspects of proteins, biomagnetism, living human cells and advanced materials, and they may play a role in a wide variety of other sensing and imaging applications for which they are perhaps uniquely qualified.