122-channel SQUID instrument for investigating the magnetic signals from the human brain

Antti I. Ahonen, Matti Hämäläinen, Matti Kajola, Jukka Knuutila, Petteri Laine, Olli V. Lounasmaa, Lauri Parkkonen, Juha Simola, Claudia D. Tesche

Research output: Contribution to journalArticleScientificpeer-review

Abstract

A 122-channel d.c. SQUID magnetometer with a helmet-shaped detector array covering the subject's head has been operational in the Low Temperature Laboratory of the Helsinki University of Technology since June 1992. The new system allows simultaneous recording of magnetic activity all over the head. The probe employs 122 planar first-order thin-film gradiometers in dual units with two exactly orthogonal channels at 61 measurement sites. The performance of the device is analyzed and compared with more conventional axial gradiometer arrays by considering signal-to-noise ratios, spatial sampling theory, confidence intervals for the estimated equivalent current dipole positions, and information-theoretical channel capacity. The signal-to-noise ratio and the resolution of the planar and axial arrays with the same number of channels are found practically equal. The number of channels and their spacing in our new Neuromag-122 system are found fully adequate for neuromagnetic measurements. An example of whole cortex recordings of auditory evoked brain activity is presented and analyzed.
Original languageEnglish
Pages (from-to)198-205
JournalPhysica Scripta
VolumeT49
Publication statusPublished - 1993
MoE publication typeA1 Journal article-refereed

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    Ahonen, A. I., Hämäläinen, M., Kajola, M., Knuutila, J., Laine, P., Lounasmaa, O. V., ... Tesche, C. D. (1993). 122-channel SQUID instrument for investigating the magnetic signals from the human brain. Physica Scripta, T49, 198-205.