Compact and easy-operation magnetocardiograph with four-channel planar gradiometers

A magnetocardiograph (MCG), which consists of a sensor comprising four superconducting-quantum-interference device (SQUID) gradiometers and a magnetic shielding cylinder made of nanocrystalline soft magnetic materials, has been developed. The sensor can be handled easily because the gradiometers are made of high-critical-temperature (Tc) superconductor operated in liquid nitrogen. Further, the shielding cylinder is lightweight (160 kg) and compact (2 m long and 1 m in diameter). The gradiometer balance is high enough (typically 0.1%) for recording magnetocardiograms inside the shielding cylinder, whose shielding factor is -35 dB at 1 Hz. We used the new MCG to record magnetocardiograms of a healthy volunteer at four different positions. From this magnetocardiograms we then obtained a current arrow map, by which myocardium activity can be estimated, at 16 sites (4 × 4 matrix) on the measurement plane. The similarity between the current-arrow map obtained by a conventional MCG and that from the newly developed MCG indicates that the developed compact MCG is also capable of estimating the region of cardiac activity.