Applications of the signal space separation method

TLDR

Biomagnetic measurements are limited by external interference, movement artifacts, and variability in subject position or sensor configuration, and SSS is based on a basis spanning all multichannel magnetic signals. SSS transforms multichannel magnetic data into device‑independent, uncorrelated idealized channels, separating biomagnetic and external interference components based on Maxwell’s equations and sensor geometry, allowing biomagnetic signals to be reconstructed by excluding interference. SSS suppresses external interference, standardizes subject position and sensor configuration, compensates for movement‑induced distortions, removes sporadic sensor artifacts, aids device calibration, extracts biomagnetic DC fields, and supports active compensation, thereby overcoming many limitations of traditional biomagnetic measurements.

Abstract

The reliability of biomagnetic measurements is traditionally challenged by external interference signals, movement artifacts, and comparison problems caused by different positions of the subjects or different sensor configurations. The Signal Space Separation method (SSS) idealizes magnetic multichannel signals by transforming them into device-independent idealized channels representing the measured data in uncorrelated form. The transformation has separate components for the biomagnetic and external interference signals, and thus, the biomagnetic signals can be reconstructed simply by leaving out the contribution of the external interference. The foundation of SSS is a basis spanning all multichannel signals of magnetic origin. It is based on Maxwell's equations and the geometry of the sensor array only, with the assumption that the sensors are located in a current free volume. SSS is demonstrated to provide suppression of external interference signals, standardization of different positions of the subject, standardization of different sensor configurations, compensation for distortions caused by movement of the subject (even a subject containing magnetic impurities), suppression of sporadic sensor artifacts, a tool for fine calibration of the device, extraction of biomagnetic DC fields, and an aid for realizing an active compensation system. Thus, SSS removes many limitations of traditional biomagnetic measurements.