• 대한동의생리학회:학술대회논문집
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• 2005.02a
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• pp.24-24
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• 2005

• Progress in Superconductivity
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• v.11 no.1
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• pp.30-35
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• 2009

We have investigated the characteristics of a superconductive Pb shield for hemispherical shape and plate to improving signal-to-noise ratio(SNR) of biomagnetism. We measured the shielding factor for the position of helmet shape Pb and for changing the distance from Pb surface. To make a uniform magnetic field, a $1.5m{\times}1.5m$ set of the helmholtz coils activated at several frequencies. The shielding factor of hemispherical shape Pb was from 20 to 57 dB and of Pb plate was about $6{\sim}26dB$ as a function of distance from the lead surface. The shielding factor was rapidly reduced as increasing the distance from Pb surface. The white noise of superconductive quantum interference device(SQUID) with a superconductive shield was about $12fT/Hz^{1/2}$ at 1 Hz, $7fT/Hz^{1/2}$ at 100 Hz. The white noise was more increased about two times than conventional SQUID system without Pb shielding. An auditory signal was measured by first order gradiometer and magnetometer with Pb superconductive shield and compared the SNR. The SQUID system with Pb shield had better performance at low frequency noise level.

• Progress in Superconductivity
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• v.4 no.2
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• pp.114-120
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• 2003

We employed a method eliminating a temporally partial principal component (PC) of multichannel-recorded neuromagnetic fields for excluding spatially correlated noises from event-evoked signals. The noises in magnetoencephalography (MEG) are considered to be mainly spontaneous neuromagnetic fields which are spatially correlated. In conventional MEG experiments, the amplitude of the spontaneous neuromagnetic field is much lager than that of the evoked signal and the synchronized characteristics of the correlated rhythmic noise makes it possible for us to extract the correlation noises from the evoked signal by means of the general PC analysis. However, the whole-time PC of the fields still contains a little projection component of the evoked signal and the elimination of the PC results in the distortion of the evoked signal. Especially, the distortion will not be negligible when the amplitude of the evoked signal is relatively large or when the evoked signals have a spatially-asymmetrical distribution which does not cancel out the corresponding elements of the covariance matrix. In the period of prestimulus, there are only the spontaneous fields and we can find the pure noise PC that is not including the evoked signal. Besides that, we propose a method, called the extended temporal decorrelation method (ETDM), to suppress the distortion of the noise PC from remanent evoked signal components. In this study, we applied the Partial Principal component elimination method (PPCE) and ETDM to simulated signals and the auditory evoked signals that had been obtained with our homemade 37-channel magnetometer-based SQUID system. We demonstrate here that PPCE and ETDM reduce the number of epochs required in averaging to about half of that required in conventional averaging.

• 한국초전도학회:학술대회논문집
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• v.13
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• pp.48-48
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• 2003

• 한국초전도학회:학술대회논문집
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• v.11
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• pp.32-32
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• 2001

• 대한동의생리학회:학술대회논문집
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• 2005.07a
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• pp.10-10
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• 2005

• 한국초전도학회:학술대회논문집
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• v.11
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• pp.6-6
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• 2001

• Progress in Superconductivity
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• v.12 no.1
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• pp.57-61
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• 2010

We have developed a whole-head MEG system for basic brain research and clinical application. The sensor system consists of a 152 SQUID gradiometer array oriented and located in a suitable way to cover a whole head of the human. The system measures magnetic fields generated by neuronal currents in the brain to get information on the brain activities. For this purpose, the field sensitivity determined by the position, orientation and geometry of the pickup coil as well as amplification factor of the electronic circuits should be known precisely. However, the position and orientation of the pickup coil might be changed from the designed specifications during cool down of the dewar and it is necessary to characterize the field sensitivity. In this study, we made calibration systems to determine the actual position and orientation of the 152 pickup coils and compared the localization results of the N100m source in the auditory cortex.

• 한국초전도학회:학술대회논문집
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• v.13
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• pp.59-59
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• 2003

• 한국초전도학회:학술대회논문집
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• v.12
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• pp.43-43
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• 2002