Magnetocardiograms Recorded by First-Order Gradiometers Using HTS rf SQUIDs

State of the art HTS SQUID sensors have already attained a sensitivity which makes them interesting for biomagnetical and especially cardiological applications. Many high quality measurements of magnetic signals emanating from the human heart have been performed with HTS sensors. With the improvement in sensitivity, the cancellation of environmental noise became one of the major problems for measuring high quality MCGs. Therefore, most of these measurements have been performed in expensive magnetically shielded rooms (MSRs) with high shielding factors (e.g. PTB, Berlin, Germany or SSL, Japan). A different, less expensive approach is the use of gradiometric arrangements of the sensors to cancel environmental disturbances. As a compromise, moderate shielding may be combined with gradiometry to keep the effort on both alternatives to a minimum.