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Magnetocardiography

is a powerful technique to measure the electrophysiological processes of the human heart beat. Even the extremely weak magnetic signals of unborn babies can be detected in a real-time measurement above the mother's womb.

The magnetic signal of the adult human heart is extremely small: only about 100 pT (peak-to-peak) above the chest. Therefore, a gradiometric sensor arrangement and suitable magnetic shielding SQUID are required for MCG recordings.

Our SQUID system for magnetocardiography (MCG) consists of six magnetometers, four measurement SQUIDs and two reference sensors which are located 10 cm and 20 cm above the measurement sensors, respectively. Each sensor consists of a YBCO step-edge rf magnetometer with a 3.5 mm diameter washer, coupled to a 10 mm × 10 mm SrTiO3 substrate resonator, and is flip-chip-coupled to a 18 mm diameter flux focuser. The resultant magnetometer field sensitivity of 20 – 30 fT/rt(Hz) at 77 K proved to be sufficient for recording adult and even fetal magnetocardiograms in our magnetically shielded room.

MCG measurementAdult magnetocardiography

The challenge for measuring human magnetocardiograms is the suppression of environmental disturbance magnetic fields. Our magnetically shielded room attenuates the magnetic fields from outside by about a factor of 400. Additional suppression is performed by a difference technique, the so-called gradiometry. The sensors directly above the chest record the magnetic field of the heart plus remaining external disturbance fields. The reference sensor located 20 cm above the chest only measures these disturbance field because the heart signal rapidly reduces with distance. Thus, the difference yields the heart signal.

Fetal magnetocardiography (fMCG) is a promising technique for prenatal diagnosis of congenital heart defects. The magnetic field of the fetal heart is difficult to record because of the small heart size. The magnetic signal reduces dramatically with increasing distance between the heart and the sensor. Because our four channel MCG system only covers a small area, it is very difficult to find the optimum position for recording. Magnetocardiograms of unborn babies which give signals of only a few pT have been successfully recorded as early as the 31st week of gestation.

Fetal MCG signalReal-time fetal MCG during 32nd week of gestation

The measured real-time trace exhibits both the fetal heart signal and the maternal heart signal. The SQUID gradiometer system noise was about 1.5 pT peak-to-peak. The QRS peak of the fetal heart beat was about 6 pT, resulting in a SNR of about 4 in the real-time data. In order to enhance the SNR, the maternal heart beats were identified by correlation analysis, averaged and subtracted. In the resulting signal, all the fetal beats were identified and beats which correlated well with a fetal QRS template were averaged over 75 s.

Additional Information

Contact:

Prof. Dr. Hans-Joachim Krause
Tel.:  +49-2461-61-2955
e-mail: h.-j.krause@fz-juelich.de

More Information

 

Research Group

Magnetic Field Sensors

 

 

Publications:

Zhang, Y., Wolters, N., Lomparski, D., Zander, W., Banzet, M., Schubert, J., Krause, H.-J., van Leeuwen, P., Multi-Channel HTS rf SQUID Gradiometer System Recording Fetal and Adult Magnetocardiograms, IEEE Trans. Appl. Supercond. 15 (2005) 631-634.

 

Zhang, Y.; Wolters, N.; Lomparski, D.; Zander, W.; Banzet, M.; Schubert, J.; Krause, H.-J.; van Leeuwen, P., Recording fMCG and adult MCG using multi-channel HTS rf SQUID gradiometers, International Congress Series 1300 (2007) 769-772.

 

Zhang, Y., Wolters, N., Lomparski, D., Zander, W., Banzet, M., Schubert, J., Krause, H.-J., Geue, D., van Leeuwen, P., Foetal magnetocardiography with a multi-channel HTS rf SQUID gradiometer, Superconductor Science and Technology 19 (2006) S266-S270.


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