What Is Biomagnetics?

Biomagnetics is the field of study concerned with the magnetic fields produced by biological organisms and with the effects of external magnetic fields on living tissues. Every organ that generates electrical currents, including the heart, brain, and skeletal muscle, also produces an associated magnetic field, typically measured in the femtotesla to picotesla range. Biomagnetics draws on physics, physiology, and biomedical engineering to detect, interpret, and apply these fields in clinical and research settings. The discipline also encompasses the biological effects of applied magnetic fields, such as those used in transcranial magnetic stimulation and magnetic resonance imaging.

The field traces its origins to the 1960s, when physicist Gerhard Baule and engineer Richard McFee recorded the first magnetocardiogram, the magnetic signal of the beating heart, using a room-temperature induction coil. Subsequent advances in superconducting quantum interference device (SQUID) technology made it possible to detect far weaker signals, opening the study of the brain's magnetic activity.

Magnetoencephalography

Magnetoencephalography (MEG) is the primary diagnostic and research technique within biomagnetics for studying the brain. MEG instruments record the magnetic fields produced by the synchronized electrical activity of neural populations, using arrays of SQUID sensors housed in magnetically shielded rooms. Because magnetic fields pass through the skull and scalp with minimal distortion, MEG provides better spatial resolution of cortical sources than electroencephalography (EEG) in many configurations, and its millisecond temporal resolution allows researchers to track rapid neural dynamics. The National Institutes of Health has supported MEG research for applications in mapping epileptic foci, studying language processing, and assessing brain connectivity in neurological disorders.

Magnetocardiography and Other Organ Measurements

Magnetocardiography (MCG) records the magnetic field of cardiac electrical activity without the contact electrodes required by conventional electrocardiography (ECG). Because MCG can map the spatial distribution of cardiac currents across the chest surface, it offers additional diagnostic information about arrhythmias and ischemia that ECG alone may not capture. Magnetogastrography and magnetomyography extend the same measurement principle to the stomach and skeletal muscles, respectively. Each of these techniques depends on SQUID-based systems or, increasingly, on optically pumped magnetometers (OPMs), which can operate at room temperature and allow sensor arrays to be placed closer to the body surface. Research published in Biomagnetism: The First Sixty Years (PMC) surveys how these measurement modalities have developed since the field's founding.

Magnetic Stimulation and Therapeutic Applications

Transcranial magnetic stimulation (TMS) applies a rapidly changing magnetic field to the scalp, inducing localized electrical currents in cortical tissue without surgical intervention. TMS is approved by the U.S. Food and Drug Administration for treating major depressive disorder that has not responded to medication, and it is under investigation for obsessive-compulsive disorder, post-traumatic stress disorder, and chronic pain. Repetitive TMS (rTMS) protocols vary in frequency and intensity to produce either excitatory or inhibitory effects on targeted cortical regions. Transcranial magnetic stimulation differs from static magnetic field exposure (as in MRI) in that it is specifically designed to modulate neural activity rather than to image tissue structure.

Applications

Biomagnetics has applications in a wide range of disciplines, including:

• Clinical neurology, for presurgical mapping of eloquent cortex in epilepsy patients
• Cardiology, through non-contact magnetocardiographic monitoring of arrhythmias
• Psychiatry, through transcranial magnetic stimulation treatment of depression
• Fundamental neuroscience research on cognition, perception, and motor control
• Materials science, in developing shielding and sensor technologies for weak-field measurements