Detection and Analysis of Magnetic Fields Produced by Bioelectric Currents in Humans

Abstract

Measurements of the ac and dc magnetic fields produced by natural internal ion currents in living systems are useful in principle because they can reduce or bypass the limitations of surface voltage measurements. The magnetic field from the normal human heart was first detected by two groups using gradient detectors and little or no shielding. The fields arose from the same ion currents seen on the ECG, and were ∼5×10−7 G at QRS maximum. Using a well shielded room and a detector consisting of a compact coil feeding a parametric amplifier, the following measurements have been made by the author: (1) mapping the heart's magnetic field around the torsos of one abnormal and six normal human subjects, verifying a previously proposed model; (2) mapping a coarse distribution of the magnetic field (∼10−9 G) around the human head produced by the same alpha-rhythm currents conventionally seen on the EEG; (3) exploring the dc field around the abdomen, which has a maximum of ∼10−6 G and is of undetermined origin. Further evaluation of data and experiments are necessary to see if the theoretical benefits of surface magnetic field measurements can be conveniently realized in practice.