A high-temperature rf SQUID system for magnetocardiography

A first-order axial electronic gradiometer having a baseline of 10 cm has been constructed by assembling two YBa\+v\2\-v\Cu\+v\3\-v\O\+v\7-\#d\\-v\ RF SQUID magnetometers with coplanar tank resonators, each having a white magnetic field resolution of about 20 fT Hz\+sp\-1/2\-sp\ at 77 K. Magnetocardiographic (MCG) measurements on human subjects using this system have been conducted in a magnetically shielded room. A team of physicians, assisted by two of the authors, used the equipment over 10 months to perform MCG measurements in a study of 80 clinical patients with cardiac arrhythmia problems and healthy persons. The system's performance was stable over the whole period. (Original abstract - amended)