Multichannel SQUID System With Integrated Magnetic Shielding for Magnetocardiography of Mice

A multichannel low transition temperature SQUID magnetometer system with integrated superconducting magnetic shielding is described, which is intended for recording the magnetocardiogram (MCG) of mice in a biolaboratory environment. The Dewar has a horizontal warm bore surrounded by a superconducting niobium shield. The mouse is situated in the center of the warm bore close to the SQUID magnetometers while its MCG is measured. We have characterized the system by determining the shielding behavior of the magnetic shield and by measuring the magnetic noise. We determined the attenuation of an external magnetic dipole field to be better than 10^-6 in the warm bore and better than 10^-7 at the magnetometer positions. The magnetic flux density noise of the system above 10 Hz is 2.7 fT/ radicHz, thus about twice as high as the intrinsic noise of the magnetometers. We determined the system performance by detecting the MCG of mice. Important physiological features like P-wave, QRS complex and T-wave could be resolved.