Here we present new MCG-systems of CRYOTON. They were designed and fabricated according to commercial orders of our customers in 2003 - 2004 years. These systems are installed in a real clinics - Franz-Volhard-Klinik (Berlin, Germany) and Bakoulev Research Center of Cardiosurgery (Moscow, Russia). The MCG-system MCG-6073-GM operates without any magnetic shielding, demonstrates a good stability in use and a desired quality of logged MCG-data.

Measuring MagnetoCardioGraphic (MCG) systems of Models MCG-6073-G and MCG-6073-GM

Measuring MCG-systems MCG-6073-G and MCG-6073-GM are intended for studies of cardiac magnetic signals in the 0-500 Hz band, with regular grid of 42 points (2x3 scale), via mapping of the heart magnetic signal and reconstruction of its sources.

MCG-system MCG-6073-GM based the fiberglass cryostat of  the Model LH-12.0-NTE  with the next  characteristics:

Cryostat LH-12.0-NTE needs the refilling procedure once a week to keep the liquid helium at all times

The measuring probes of the signal channels are mounted on the separated fiberglass tubes. Each   probe contains:

•  the fine balanced 2-nd order gradiometer;

•  the dc-SQUID sensors CC-blue ( see at www.supracon.de )

• elements for coupling of the dc-SQUID with the pre-amplifier;

The signal 2-nd order gradiometer is made of the insulated 0.07 mm diameter Nb wire on the carbon support of 20 mm in diameter. The gradiometer base is 60 mm; the initial imbalance does not exceed 0.1%. The internal noise level of the probes is less than 10 fT/ Hz^1/2;

XYZ reference magnetometer is mounted inside the central probe and located outside the area of signal gradiometers. Three dc-SQUID-magnetometers are mounted on the orthogonal surfaces of the 12 mm cube and produce the reference signals for the Electronic Noise Suppression System (ENSS).

The system electronics Model E-1112 contains 10 similar electronics channels assembled in a single aluminum box. Each channel of electronics contains the analog and digital part. The analog part is working in the modulation scheme with zero-point detection and with current feedback (the magnetic flux feedback presents as option); it allows for tuning of the SQUID into its working regime. The digital part allows for tuning of the SQUIDs through a USB-port.

The level of self-noise of the electronics pre-amplifier does not exceed 0.7 nV/Hz^1/2. The electronics has two ranges with respect to the feedback depth: 0.1V/F₀ and 1V/F_0. The bandwidth of the electronic signal in the closed feedback regime is 0 - 50 kHz at the -3 dB level, for a 0.1 F₀ signal.

The SQUID electronics-box has dimensions 260x250x90 mm, and locates on the cryostat holder near the probe flange.

Magnetometer control block CU-310 contains stabilized power source, additional output signal amplifiers, band filters, ENSS (Electronic Noise Suppression System), 24-bit ADC-converters and means for system tuning, MCG-signals processing, digitizing and MCG-data transferring to PC. The use of the ENSS improves the balancing of gradiometers more than 20 times.

The original software for MCG-data processing was developed and tested in the real clinical measurements and destined for:

- non-invasive mapping of the heart magnetic field over the human body with the regular grid in unshielded environment; synchronous input of the MCG- and ECG-signal into the PC;

- filtering, averaging and sorting of the MCG-data; interpolation of the averaged MCG-data and construction of the "instantaneous" maps of the magnetic field distribution in the surface of measurements;

- analytical localizing of the source of the electromagnetic activity and its movement trajectory on the investigated interval of the cardiac cycle;

- reconstruction of the biomagnetic source as a planar current distribution;

- spatial-temporal analysis of the MCG-signal and numerical characterization of the heart magnetic field without application of the inverse solution procedure;

- creating of friendly graphic interface and flexible database the results of measurements and analysis;

          A possible configurations of CRYOTON's measuring MCG-systems: