Abstract
Magnetography with superconducting quantum interference device (SQUID) sensor arrays is a well-established technique for measuring subtle magnetic fields generated by physiological phenomena in the human body. Unfortunately, the SQUID-based systems have some limitations related to the need to cool them down with liquid helium. The room-temperature alternatives for SQUIDs are optically pumped magnetometers (OPM) operating in spin exchange relaxation-free (SERF) regime, which require a very low ambient magnetic field. The most common two-layer magnetically shielded rooms (MSR) with residual magnetic field of 50 nT may not be sufficiently magnetically attenuated and additional compensation of external magnetic field is required. A cost-efficient compensation system based on square Helmholtz coils was designed and successfully used for preliminary measurements with commercially available zero-field OPM. The presented setup can reduce the static ambient magnetic field inside a magnetically shielded room, which improves the usability of OPMs by providing a proper environment for them to operate, independent of initial conditions in MSR.
Highlights
Electrophysiological phenomena in the human body lead to the occurrence of magnetic field [1].While electric biosignals are affected by the presence of insulating layers and varied conductivity of the body tissues, magnetic field can penetrate through
While the theoretical basis of the residual field compensation is known and advanced compensating systems are commercially available [45,46,47], we present a customized design to the certain application: working with optically pumped magnetometers (OPM) inside magnetically shielded rooms (MSR)
Zero-field optically pumped magnetometers require a close to zero residual magnetic field
Summary
Electrophysiological phenomena in the human body lead to the occurrence of magnetic field [1]. While electric biosignals are affected by the presence of insulating layers (fat, bones) and varied conductivity of the body tissues, magnetic field can penetrate through. Contactless measurements using magnetometers can avoid difficulties related to the electrode’s attachment to the skin. Measurements of the fields generated by the ionic currents flowing through the fibers of the cardiac muscle (magnetocardiography (MCG) [2]), activity of the cerebral cortex neurons (magnetoencephalography (MEG) [3]) or detection of iron stores (liver susceptometry [4]) are already implemented in clinical practice [5,6,7]. Study on fetal development (fetal magnetocardiography (fMCG) [13], fetal magnetoencephalography (fMEG) [14])
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