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Review
. 2023 Apr 23;23(9):4218.
doi: 10.3390/s23094218.

Biomagnetism: The First Sixty Years

Bradley J Roth  1
Affiliations
Review

Biomagnetism: The First Sixty Years

Bradley J Roth. Sensors (Basel). .

Abstract

Biomagnetism is the measurement of the weak magnetic fields produced by nerves and muscle. The magnetic field of the heart-the magnetocardiogram (MCG)-is the largest biomagnetic signal generated by the body and was the first measured. Magnetic fields have been detected from isolated tissue, such as a peripheral nerve or cardiac muscle, and these studies have provided insights into the fundamental properties of biomagnetism. The magnetic field of the brain-the magnetoencephalogram (MEG)-has generated much interest and has potential clinical applications to epilepsy, migraine, and psychiatric disorders. The biomagnetic inverse problem, calculating the electrical sources inside the brain from magnetic field recordings made outside the head, is difficult, but several techniques have been introduced to solve it. Traditionally, biomagnetic fields are recorded using superconducting quantum interference device (SQUID) magnetometers, but recently, new sensors have been developed that allow magnetic measurements without the cryogenic technology required for SQUIDs.

Keywords: SQUID magnetometer; biomagnetism; inverse problem; magnetocardiogram; magnetoencephalogram; optically pumped magnetometer.

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Conflict of interest statement

The author declares no conflict of interest.

Figures

Figure 1
Figure 1
Noise sources in biomagnetism. The magnetic fields of the earth, heart, and brain are in pT, while the noise and SQUID sensitivity depend on frequency and are expressed in pT per root hertz. Reprinted with permission from [2]. Copyright 1993 by the American Physical Society.
Figure 2
Figure 2
Types of gradiometers.
Figure 3
Figure 3
Top: Normal MCG. Bottom: MCG with an elevated ST segment.
Figure 4
Figure 4
A cross-sectional view of the left ventricle. (Left): An isotropic tissue. (Right): Anisotropic tissue that produces a current loop around the ventricle wall.
Figure 5
Figure 5
The magnetic field of a frog sciatic nerve, as measured using a toroid.
Figure 6
Figure 6
The current and magnetic field produced by a planar wave front propagating in a two-dimensional sheet of cardiac muscle. The muscle is anisotropic, with a higher conductivity along the myocardial fibers. Reproduced with permission from [59], copyright 1999 by the IEEE.
Figure 7
Figure 7
The magnetic field at the apex of the heart. Current is green and the magnetic field is purple. Reproduced with permission from [63], copyright 1988 by Elsevier.
Figure 8
Figure 8
The magnetic field of a radial dipole is zero outside a spherical conductor.
See this image and copyright information in PMC

References

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