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We have measured biomagnetic signals in rat by using a high-TC SQUID magnetometer system employing a small magnetically shielded box. For the rat cardiac magnetic field measurements, a healthy rat with body weight of about 350 g was anesthetized and fixed on a plastic xyz-stage in supine position inside the magnetically shielded box. We could obtain strong R-peak amplitude up to 56 pT with well defined P-, QRS-, T-wave, and ST-segment separating T-wave from QRS complex. We measured and analysed rat MCG waveforms for 5 × 5 grid measurements covering 60 mm × 60 mm area and 12 circular measurements centered at the heart position. This work demonstrates that the potential advantages of high-TC SQUID magnetometer system in evaluating the rat MCG measurement for animal models of cardiac electrical activities.

We developed a cryocooled SQUID system with which human magnetocardiogram (MCG) and possibly magnetoenceparogram (MEG) can be measured. To reduce cyclic magnetic noises originating from the regenerator of the cold heads of the cryocooler, a superconductive shield (99.5% Pb) was used to protect the SQUID sensors, and a ferromagnetic shield (78% Ni alloy) was used to screen the cold head. In addition, the SQUID sensors' chamber was placed at a distance of 1.8 m from the cold head chamber to install the cold-head chamber outside the magnetically shielded room (MSR) for future development. The loss in cooling power due to the increased distance was compensated by increasing the number of thermal rods, and thus the SQUID sensor and superconductive shield could be refrigerated to 4.8 K and 5 K, respectively. The superconductive shield successfully rejected thermal noise emitted from metallic blocks used to improve thermal conduction. The noise of the SQUID system was 3 fT/Hz1/2, and the cyclic magnetic noise could be reduced to 1.7 pT. We could obtain a clear MCG signal while the entire cryogenics was in operation without any special digital processing.