Magnetocardiography with high-T-C gradiometers working in unshielded environments

The noninvasive measurement of magnetic heart activity based on high-T-C DC SQUIDs, could be a tool for investigating cardiac electrophysiological pro perties, if such a system is able to work in unshielded environments. For t he realization of such a system we use thin film planar SQUID gradiometers with bicrystal or step-edge Josephson junctions. Even for a small baseline of approximately 4 mm (limited by substrate dimensions), the field gradent resolution is in the range required for clinical analysis. We use a portabl e system which consists of a glass fiber cryostat with a measuring unit whe re we can place up to four sensors, different read-out electronics, and sig nal filtering methods. Firstly, measurements inside a magnetically shielded room were used to show the capability of our magnetocardiography (MCG) sys tem in medical applcations. The system works in an unshielded environment a lso, without additional field compensation. We demonstrate a measurement of a magnetocardiogram in a real clinical environment, and discuss the possib ilties as well as the limitations of this system in magnetocardiography. (C ) 1999 Elsevier Science Ltd. All rights reserved.