Discrimination of SII Activity of Three-Dimensional SEF with SVD and Time Frequency Analysis
B. S. Kim, K. Kobayashi, 高橋 篤史, 内川 義則 · Journal of the Magnetics Society of Japan · 2004
This paper describes a new method for discriminating among multiple sources in the brain overlapping in time. We carried out a three-dimensional vector measurement of bilateral somatosensory evoked field (SEF) with an electric stimulus to the right thumb, using three-dimensional second-order gradiometers connected to 39-channel SQUIDs, which can detect magnetic components perpendicular to the scalp (Br) and tangential to the scalp (Bθ, Bφ) simultaneously. The SVD method was applied to each spatiotemporal datum, having two frequencies ranges (1-40Hz, 15-40Hz), with a time window (50 ms) and was shifted every 5 ms in analysis. Two dominant singular values were obtained for the contralateral magnetic component. We applied a time-frequency analysis to bilateral magnetic data and analyzed the time course of the power spectrum. We concluded that this proposed method, using a dynamic SVD method and time-frequency analysis with different frequency ranges, is useful for discriminating among multiple sources overlapping in time.