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MEG recordings using High-Temperature SQUIDs

Today, almost all MEG systems use low temperature SQUIDs to detect the very small magnetic fields generated by the human brain. Low temperature SQUIDs (LTc) require liquid helium (-269°C) for cooling. Although the technique is well established, the requirement of liquid helium is costly as liquid helium itself is very expensive, and helium transfer requires special equipment and precautions. Due to these limitations, our research explores the use of high temperature SQUIDs.
Although high temperature SQUIDs (HTc) operating at the temperature of liquid nitrogen (-196°C) have been available for over 20 years, for a long time the intrinsic noise was too high to measure the magnetic fields generated by the human brain. However, recent improvements in sensor technology mean that the noise of HTc SQUIDs can be reduced significantly, making it feasible to detect brain signals.
Following our initial tests, preliminary results indicate that detection of evoked MEG signals is possible with HTc SQUIDs. Subsequently, we tried to localise sources of auditory evoked responses and compared the results to the data achieved with a commercial 248 channel LTc whole head MEG system. The measurements were performed in our magnetically shielded room where our 248 channel LTc MEG-system is installed and the same stimulation (auditory, 1000 Hz beeps, 50 ms, ca 300 trials) was used for both systems. The figures show the results of a measurement with the LTc system (blue), and 16 recordings in different positions with the one channel HTc system (red). The blue and red markers in the MR image show the localisation results for both systems.

HTc


References

Dammers, J., Chocholacs, H., Eich, E., Boers, F., Faley, M., Dunin-Borkowski, R.E., Jon Shah, N., 2014. Source localization of brain activity using helium-free interferometer. Appl. Phys. Lett. 104, 213705. doi:10.1063/1.4880097


Faley, M.I., Gerasimov, I.A., Faley, O.M., Chocholacs, H., Dammers, J., Eich, E., Boers, F., Shah, N.J., Sobolev, A.S., Slobodchikov, V.Y., Maslennikov, Y. V., Koshelets, V.P., Dunin-Borkowski, R.E., 2015. Integration Issues of Graphoepitaxial High- Tc SQUIDs Into Multichannel MEG Systems. IEEE Trans. Appl. Supercond. 25, 1–5. doi:10.1109/TASC.2014.2365098


Faley, M.I., Poppe, U., Borkowski, R.E.D., Schiek, M., Boers, F., Chocholacs, H., Dammers, J., Eich, E., Shah, N.J., Ermakov, A.B., Slobodchikov, V.Y., Maslennikov, Y.V., Koshelets, V.P., 2012. Magnetoencephalography using a Multilayer hightc DC SQUID Magnetometer. Phys. Procedia 36, 66–71. doi:10.1016/j.phpro.2012.06.131


Faley, M.I., Poppe, U., Dunin-Borkowski, R.E., Schiek, M., Boers, F., Chocholacs, H., Dammers, J., Eich, E., Shah, N.J., Ermakov, A.B., Slobodchikov, V.Y., Maslennikov, Y. V., Koshelets, V.P., 2013. High-Tc DC SQUIDs for Magnetoencephalography. IEEE Trans. Appl. Supercond. 23, 1600705–1600705. doi:10.1109/TASC.2012.2229094


Faley, M., Gerasimov, I., Faley, O., Chocholacs, H., Dammers, J., Eich, E., Boers, F., Shah, N., Sobolev, A., Slobodchikov, V., Maslennikov, Y., Koshelets, V., Dunin-Borkowski, R., 2014. Integration issues of graphoepitaxial high-Tc SQUIDs into multichannel MEG systems. IEEE Trans. Appl. Supercond. PP, 1–1. doi:10.1109/TASC.2014.2365098s