Noise Reduction of DC Measurements based on Neuronal Network Data Processing
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1
Physikalisch-Technische Bundesanstalt, Germany
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2
BioMed Jena, Germany
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3
University of Applied Science Jena, Department of Medical Engineering, Germany
Measurements of biomagnetic signals below 0.1 Hz are compromised by an increased noise level for two reasons. The contribution of the environmental magnetic noise is much higher than for high frequencies. And the shielding efficiency of magnetically shielded rooms is inferior. We present a new tool to improve the signal-to-noise ratio of those measurements by almost factor 100. One or more reference sensors are positioned far from the signal source of interest, so that any source input into the reference sensors is negligible. In order to pick up all magnetic noise components a 3 axis SQUID (or fluxgate) sensor is recommended as reference. In contrast to conventional gradiometer techniques no delicate sensor balancing is needed and no signal amplitude losses occur. Due to the short processing time the filter can operate in real time and is suitable for multi channel systems. All measurements start with a training period only recording the noise. Based on these data, the filter “learns” a functional relation between the noise in each sensor signal and each reference signal. After that, in the measurement phase, the noise is subtracted by using these filter functions. The deduced functions vary according to the amount of unwanted interference signals, i.e. urban activity generates low frequency signals according to the time of day. Firstly, we demonstrate the quality of our tool by detecting two well-known technical signals in noisy environment. Then, we show that this tool enables near dc MEG measurements with a conventional SQUID setup in a shielded room with only two permalloy layers. As another application we improve relaxation measurements of magnetic nanoparticles (MRX) accumulated in tissue samples in a noisy environment by using this technique. Thus, our neural network based filtering opens up new measurement possibilities in a broad range of magnetic dc phenomena.
Conference:
Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010.
Presentation Type:
Poster Presentation
Topic:
Instrumentation and Multi-modal Integrations: MEG, Low-field MRI,EEG, fMRI,TMS,NIRS
Citation:
Mueller
W,
Knappe-Grueneberg
S,
Koerber
R,
Richter
H,
Sander
T,
Wiekhorst
F,
Burghoff
M,
Gablenz
T and
Herrmann
L
(2010). Noise Reduction of DC Measurements based on Neuronal Network Data Processing.
Front. Neurosci.
Conference Abstract:
Biomag 2010 - 17th International Conference on Biomagnetism .
doi: 10.3389/conf.fnins.2010.06.00413
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Received:
09 Apr 2010;
Published Online:
09 Apr 2010.
*
Correspondence:
Tilmann Sander, Physikalisch-Technische Bundesanstalt, Berlin, Germany, tilmann.sander-thoemmes@ptb.de