Kenichi Sata

A CRYOCOOLED 61-CHANNEL MEG SYSTEM

Abstract An LTS-SQUID-based MEG system cooled by a GM/JT cryocooler was manufactured, and its clinical performance was estimated. The system consists of 61 axial gradiometer channels arranged on a spherical surface. The white noise level of the system was below 20 fT/Hz1/2. The periodic noise induced by the cryocooler could be eliminated by using a digital noise subtraction process. We measured the somatosensory evoked magnetic field of the human brain.

A cryocooled helmet-shaped MEG measurement system

We developed a cryocooled helmet-shaped magnetoencephalographic measurement system. We determined the sources of white noise that contribute to the total white noise of this system and determined the source of cyclic noise generated by the Gifford-McMahon-Joule-Thomson cryocooler. Design modifications based on these results will reduce the white noise of our future cryocooled systems to 5 fT Hz-1/2 for cyclic noise to 1 pT.

A Cryocooled SQUID System with Minimal Clearance Between the Pick-up Coil and the Specimen

We have developed a SQUID system that have a clearance of about 3 mm between the pick-up coil and the specimen and is cooled by a Gifford-McMahon (GM)/Joule-Thomson (JT) cryocooler. Previous work showed that cryocooled SQUID systems, which do not require liquid helium, can successfully measure biomagnetic fields [1][2][3]. To eliminate the noise caused by the cryocooler, such systems either utilize digital filters or interrupt the cooler expansion operation during the measurements. In our new system, however, we reduced this noise by replacing the ferromagnetic materials of the cryocooler, and we measured magnetcardiogram (MCG) signals in real-time without the need for interrupting the cooler expansion operation.