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김기웅,이용호,권혁찬,김진목,김인선,박용기,이규원,Kim K.,Lee Y. H,Kwon H,Kim J. M,Kim I. S,Park Y. K,Lee K. W 한국초전도학회 2004 Progress in superconductivity Vol.6 No.1
We consider design factors for a SQUID sensor array to construct a 52-channel magnetocardiogram (MCG) system that can be used to measure tangential components of the cardiac magnetic fields. Nowadays, full-size multichannel MCG systems, which cover the whole signal area of a heart, are developed to improve the clinical analysis with high accuracy and to provide patients with comfort in the course of measurement. To design the full-size MCG system, we have to make a compromise between cost and performance. The cost is involved with the number of sensors, the number of the electronics, the size of a cooling dewar, the consumption of refrigerants for maintenance, and etc. The performance is the capability of covering the whole heart volume at once and of localizing current sources with a small error. In this study, we design the cost-effective arrangement of sensors for MCG by considering an adequate sensor interval and the confidence region of a tolerable localization error, which covers the heart. In order to fit the detector array on the cylindrical dewar economically, we removed the detectors that were located at the corners of the array square. Through simulations using the confidence region method, we verified that our design of the detector array was good enough to obtain whole information from the heart at a time. A result of the simulation also suggested that tangential-component MCG measurement could localize deeper current dipoles than normal-component MCG measurement with the same confidence volume; therefore, we conclude that measurement of the tangential component is more suitable to an MCG system than measurement of the normal component.
권혁찬,김기웅,김진목,이용호,김태은,임현균,박용기,고영국,정남식,Kwon, H.,Kim, K.,Kim, J.M.,Lee, Y.H.,Kim, T.E.,Lim, H.K.,Park, Y.K.,Ko, Y.G.,Chung, N. 한국초전도학회 2006 Progress in superconductivity Vol.8 No.1
In emergency rooms, patients with acute chest pain should be diagnosed as quickly as possible with higher diagnostic accuracy for an appropriate therapy to the patients with acute coronary syndrome or for avoiding unnecessary hospital admissions. At present, electrocardiography(ECG) and biochemical markers are generally used to detect myocardial infarction and coronary angiography is used as a gold standard to reveal the degree of narrowing of coronary artery. Magnetocardiography(MCG) has been proposed as a novel and non-invasive diagnostic tool fur the detection of cardiac electrical abnormality associated with myocardial ischemia. In this study, we examined whether the MCG can be used fur the detection of coronary artery disease(CAD) in patients, who were admitted to the emergency room with acute chest pain. MCG was recorded from 36 patients admitted to the emergency room with suspected acute coronary syndrome. The MCG recordings were obtained using a 64-channel SQUID MCG system in a magnetically shielded room. In result, presence of CAD could be found with a sensitivity of 88.2 % in patients with acute chest pain without 57 elevation in ECG, demonstrating a possible use in the emergency room to screen CAD patients.
Classification of magnetocardiographic maps in coronary artery disease diagnosis
권혁찬,김기웅,김진목,이용호,김태은,임현균,고영국,정남식,Kwon H.,Kim K.,Kim J. M.,Lee Y. H.,Kim T. E.,Lim H. K.,Ko Y. G.,Chung N. The Korean Superconductivity Society 2005 Progress in superconductivity Vol.7 No.1
The diagnostic management of patients with chest pain remains a clinical challenge. Magnetocardiography (MCG) has been proposed as a new non-invasive method for detection of myocardial ischemia. To date, however, MCG technique is not intensively introduced for clinical use. One of the main reasons might be the absence of statistically valid and diagnostically clean criteria, which can determine the presence of certain heart disease. In this work, we suggested a new method to classify the diagnostic value of MCG for the detection of coronary artery disease (CAD) in patients with chest pain. MCG was recorded for three groups (healthy subjects and patients without and with CAD) by means of the 64 channel SQUID gradiometer system installed at a hospital. Using four parameters, which were found to be significantly different between groups, we evaluated a probability, in which parameters can be classified into each group based on the distribution function of the parameter in each group. For all parameters, sum of probabilities was compared between groups to determine the presence of CAD. Our classification method shows that the MCG can be a useful tool to predict the presence of CAD with sensitivity and specificity of higher than $80\%$ each.
진공조에 위치한 1차 SQUID 미분계를 이용한 헬멧형 뇌자도 장치의 제작
유권규,김기웅,이용호,Yu, K.K.,Kim, K.,Lee, Y.H.,Kim, J.M. 한국초전도학회 2009 Progress in superconductivity Vol.11 No.1
We have fabricated a helmet type magnetoencephalogrphy(MEG) with a $1^{st}$ order gradiometer in vacuum to improve the signal-to-noise ratio(SNR) and the boil-off rate of liquid helium(LHe). The axial type first-order gradiometer was fabricated with a double relaxation oscillation SQUID(DROS) sensor which was directly connected with a pickup coil. The neck space of LHe dewar was made to be smaller than that of a conventional dewar, but the LHe boil-off ratio appeared to increase. To reduce the temperature of low Tc SQUID sensor and pickup coil to 9 K, a metal shield made of, such as copper, brass or aluminum, have been usually used for thermal transmission. But the metal shield exhibited high thermal noise and eddy current fluctuation. We quantified the thermal noise and the eddy current fluctuation of metal. In this experiment, we used the bobbin which was made of an alumina to wind Nb superconductive wire for pickup coil and the average noise of coil-in-vacuum type MEG system was $3.5fT/Hz^{1/2}$. Finally, we measured the auditory evoked signal to prove the reliability of coil-in-vacuum type MEG system.
강찬석,김기웅,유권규,이성주,권혁찬,황성민,이용호,김진목,이상길,Kang, C.S.,Kim, K.,Yu, K.K.,Lee, S.J.,Kwon, H.,Hwang, S.M.,Lee, Y.H.,Kim, J.M.,Lee, S.K. 한국초전도학회 2009 Progress in superconductivity Vol.10 No.2
A current limiter was manufactured using a Josephson junction array to cut off an excessive current flowing into the SQUID sensor. The Fabricateed Josephson junction array was connected in series with a flux transformer that consists of a pick-up coil and an input coil, and the flux transformer was inductively coupled with a Double Relaxation Oscillation SQUID(DROS). The flux-voltage modulation curve was induced by applying an AC magnetic field whose magnitude was far smaller than that of the DC magnetic field. A change in the flux-voltage modulation curve of the SQUID was observed while the DC magnetic field was increased, to qualitatively examine the current limiting characteristic of the Josephson junction array. As a result, it was found that the SQUID flux-voltage modulation curve disappeared at the critical current of the Josephson junction array, which indicates that the Josephson junction array properly works as a current limiter.
유권규,김기웅,강찬석,김진목,이용호,Yu, K.K.,Kim, K.,Kang, C.S.,Kim, J.M.,Lee, Y.H. 한국초전도학회 2009 Progress in superconductivity Vol.10 No.2
We have fabricated a low-noise 61-channel axial-type first-order gradiometer system for measuring fetal magnetocardiography(MCG) signals. Superconducting quantum interference device(SQUID) sensor was based on double relaxation oscillation SQUID(DROS) for detecting biomagnetic signal, such as MCG, magnetoencphalogram(MEG) and fetal-MCG. The SQUID sensor detected axial component of fetal MCG signal. The pickup coil of SQUID sensor was wound with 120 ${\mu}m$ NbTi wire on bobbin(20 mm diameter) and was a first-order gradiometer to reject the environment noise. The sensors have low white noise of 3 $fT/Hz^{1/2}$ at 100 Hz on average. The fetal MCG was measured from $24{\sim}36$ weeks fetus in a magnetically shielded room(MSR) with shielding factor of 35 dB at 0.1 Hz and 80 dB at 100 Hz(comparatively mild shielding). The MCG signal contained maternal and fetal MCG. Fetal MCG could be distinguished relatively easily from maternal MCG by using independent component analysis(ICA) filter. In addition, we could observe T peak as well as QRS wave, respectively. It will be useful in detecting fetal cardiac diseases.
권혁찬,김기웅,이용호,김진목,임현균,박용기,정남식,고영국,정보영,김진배,조정래,Kwon, H.,Kim, K.,Lee, Y.H.,Kim, J.M.,Lim, H.K.,Park, Y.K.,Chung, N.,Ko, Y.G.,Joung, B.,Kim, J.B.,Cho, J.R. 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
Myocardial ischemia causes heterogeneity of ventricular repolarization and sometimes produces changes of the ST-T wave in ECG. Therefore, morphological changes of ST-T waveform in ECG have a clinical significance in diagnosing myocardial ischemia. In this study, we investigated the ST-T changes caused by myocardial ischemia in magnetocardiography (MCG). We analyzed MCG patterns of biphasic T, ST segment deviations from baseline, main current angle of $T_{peak}$ and $T_{peak}$ dispersion in 300 CAD patients without ST elevation in ECG, 122 symptomatic patients and 48 normal subjects. MCGs were recorded by multichannel SQUID system in a magnetically shielded room. As results, we found that appearances of the abnormality were strongly correlated with the severity of myocardial ischemia. Also we found that the percentage of the patients showing MCG changes were higher than those in ECG. These results show that morphological changes of ST-T waveform in MCG can be used as a marker of myocardial ischemia.