Noise cancellation by a whole-cortex SQUID MEG system

Author

Vrba, J. ; Taylor, B. ; Cheung, T. ; Fife, A.A. ; Haid, G. ; Kubik, P.R. ; Lee, S. ; McCubbin, J. ; Burbank, M.B.

Author_Institution

CTF Syst. Inc., Port Coquitlam, BC, Canada

Volume

5

Issue

2

fYear

1995

fDate

6/1/1995 12:00:00 AM

Firstpage

2118

Lastpage

2123

Abstract

We report on the noise cancellation performance of several whole-cortex MEG systems operated under diverse noise conditions, ranging from unshielded environments to moderately shielded rooms. The noise cancellation is performed by means of spatial filtering using high order gradiometers (2nd or 3rd), which can be formed optionally either by SQUID electronics firmware or by software. The spatial dependence of the gradiometer responses was measured in an unshielded environment and compared with simulations to yield an estimate of the system common mode magnitudes relative to field, 1st, and 2nd gradients. High order gradiometers were also formed when the system was operated in moderately shielded rooms. The combination of the spatial filtering and room shielding resulted in very high combined noise rejections approaching that of high quality shielded rooms. Examples of noise cancellation under various conditions are shown.<>

Keywords

SQUID magnetometers; interference suppression; magnetic shielding; magnetoencephalography; spatial filters; superconducting device noise; SQUID electronics firmware; common mode magnitudes; high order gradiometers; moderately shielded rooms; noise cancellation performance; noise rejections; spatial filtering; unshielded environments; whole-cortex SQUID MEG system; Electroencephalography; Filtering; Magnetic noise; Magnetic separation; Microprogramming; Noise cancellation; Noise measurement; SQUIDs; Signal processing; Working environment noise;

fLanguage

English

Journal_Title

Applied Superconductivity, IEEE Transactions on

Publisher

ieee

ISSN

1051-8223

Type

jour

DOI

10.1109/77.403001

Filename

403001