Magnetocardiography (MCG), which uses a multi-channel superconducting quantum interference device (SQUID), is applicable to the non-invasive analysis of ischemic heart disease and arrhythmia. MCG systems that use a low-temperature superconductor (LTS)-SQUID enable the measurement of cardio-magnetic fields across a wide age range, from fetus to mature adult, and are capable of detecting very weak signals because the magnetic sensor is sensitive to signals above a few fT/ (Hz)1/2. Abnormalities in the current distribution of an ischemic heart and the propagation pathway for arrhythmia are thus easily detected and visualized. In the area of next-generation products, 16-channel and 32-channel high-temperature superconductor (HTS)-SQUID systems are also being developed to realize more compact systems. Some open-ended cylindrical magnetic shields were applied to HTS- and LTS-MCG systems. These cylindrical shields made a uniform magnetic field in the light magnetic shielding, and environmental noise was easily cancelled due to the uniform magnetic field inside the shielding. An improvement in HTS-SQUID sensitivity and a noise reduction technique have made real-time MCG measurement possible.
More than a decade has passed since multi-channel magnetoencepharography (MEG) systems based on superconducting quantum interference devices (SQUIDs) became commercially available. In collaboration with medical doctors, neuroscientists and engineers, MEG systems have been improved and progress continues to be made as one of the cutting-edge instruments useful for brain diagnosis and research. On the other hand, SQUID technology is also promising for new biomagnetic applications. MEG and other nerve measurement systems using SQUIDs are introduced and challenges from a technical point of view are described.