The purpose of our study is to estimate the imaging of ischemic myocardial muscles in rats. The magnetocardiograms (MCG) of rats were measured by a 12-channel high resolution gradiometer, which consisted of 5 mm diameter pick-up coils with a 7.5 mm distance between each coil. MCGs of seven male rats were measured in a magnetically shielded room pre and post coronary artery occlusion. The source imaging was estimated by minimum norm estimation (MNE). Changes of the current source imaging pre- and post coronary artery occlusion were clarified. As a result, in the ST segment, the current distribution significantly increased at the ischemic area. In the T wave, the direction of the current distribution clearly shifted to the left thorax. We proved that the increased area of the current distribution in the ST segment was related to the ischemic area of the ventricular muscles.

A multi-channel high temperature superconducting interference device (high Tc SQUID) system with high magnetic field resolution has been developed. Step edge junctions were employed as weakly coupled Josephson junctions for the SQUID. These junctions worked well and their I-V curves fit the resistively shunted junction (RSJ) model. The SQUID design was investigated to improve magnetic field resolution. The size of the SQUID's center hole was investigated, and we found the optimized size of the hole to be about 25 µm. Meissner effect of superconductor was used in order to concentrate magnetic fluxes. A large washer SQUID and a flux concentrating plate was developed to concentrate magnetic flux to the SQUID center hole. The magnetic field resolution became 370 fT/Hz at 10 Hz and 220 fT/Hz at 10 kHz. This field resolution was enough to detect biomagnetic signals such as magnetocardiac signals. The SQUID was mounted on a special chip carrier and was sealed with epoxy resin for protection from humidity. We have designed and developed a 4-channel and a 16-channel high Tc SQUID system. We used them in a magnetically shielded room to measure magnetic signals of the human heart. We obtained clear multi-channel magnetocardiac signals, which showed clear so called QRS and T wave peaks. A clear isofield contour map of magnetocardiac signals was also obtained. These data indicated that high Tc SQUID is feasible for these biomagnetic applications.