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비자기 차폐환경에서 미세자기신호 측정을 위한 고온 초전도 SQUID 자력계의 설계 및 제작
유권규 ( K. K. Yu ),김인선 ( I. S. Kim ),박용기 ( Y. K. Park ) 한국센서학회 2004 센서학회지 Vol.13 No.2
N/A We have designed and fabricated the YBCO single layer directly-coupled SQUID magnetometers for the purpose of magnetocardiography in a magnetically disturbed environment. The SQUID magnetometers were designed three different types of pickup coil such as solid type, PL type I and PL type II for further stable fluxed-locked-loop operation without magnetic shielding. Magnetometer was fabricated with a single layer YBCO thin film deposited on STO(100) bicrystal substrate with misorientation angle of 30°. We have achieved a magnetic field noise BN of 30 fT/Hz^(1/2) at 100 Hz, and less than 70 fT/Hz^(1/2) at 1 Hz. The PL type IISQUIDs have exhibited the most stable fluxed-locked-loop operation in a magnetically unshielded environment.
이용호(Y. H. Lee),권혁찬(H. C. Kwon),김진목(J. M. Kim),임청무(C. M. Lim),이상길(S. K. Lee),박용기(Y. K. Park),박종철(J. C. Park) 한국자기학회 1996 韓國磁氣學會誌 Vol.6 No.4
A magnetically shielded room has been constructed for biomagnetic applications. The room has internal dimensions of 2 m(length)×2 m(width)×2.5 m(height) and it consists of high permeability Mumetal and high conductivity aluminum, utilizing ferromagnetic shielding and eddy current shielding. The dc shielding factor around the center of the room is above 60 ㏈, and the ac shielding factors at 1 and 10 ㎐ are larger than 60 and 80 ㏈, respectively. The internal magnetic field noise at 1 ㎐ is 500 fT/√㎐ and at 10 ㎐ is 100 fT/√㎐, and the field gradient noise at 1 ㎐ is below 7 fT/㎝√㎐. Successful measurements of cardiomagnetic fields using SQUID magnetometer and neuromagnetic fields using SQUID gradiometer have been done.
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.
김진목,이용호,권혁찬,유권규,김기웅,박용기,Kim, J.M.,Lee, Y.H.,Kwon, H.,Yu, K.K.,Kim, K.,Park, Y.K.,Sasada, Ichiro 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
We have installed a 61-channel magnetocardiography (MCG) system inside a magnetically shielded room (MSR) with a size of $2.4\;m\;{\times}2.4\;m\;{\times}2.4\;m$. The MCG system consists of 1st-order axial gradiometers containing double relaxation oscillation SQUIDs (DROSs) with pick-up coils of a base line of 70 mm. The MSR holds a shielding factor of 50 at 0.1 Hz and 10000 at 100 Hz, when its door in the middle on a front wall is closed. On opening the MSR door, we have obtained the characteristics of the MCG system with a 2.9 Hz noise generated from an air conditioning unit at 13 m distance off the MSR. In an open-door MSR ($140^{\circ}$ opening), a noise at the center channel increases up to $700\;fT/Hz^{l/2}$ at 2.9 Hz and $1.7\;pT/Hz^{1/2}$ at 60 Hz. MCG signals for a healthy human do not show distortion until the door opens to $45^{\circ}$, but show the effect of noise when the door opens further at $90^{\circ}$ and $140^{\circ}$. With the door opens to $45^{\circ}$, MCG measurement can be performed with ease of door operation and without creating claustrophobia for the patient.
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
Magnetocardiography(MCG) has been proposed as a novel and non-invasive diagnostic tool for the detection of cardiac electrical abnormality associated with myocardial ischemia. In our previous study, we have proposed a new classification method of MCG parameters, based on the different populations of the parameters between coronary artery disease(CAD) patients, symptomatic patients and healthy volunteers. We used four parameters, representing the directional changes of the electrical activity in the period of an R-ST-T interval. In patients with chest pain and without ST-segment elevation, who were selected consecutively from all patients admitted to the hospital in 2004, the patients with CAD could be classified with a higher sensitivity than conventional methods, showing that the proposed method can be useful for the diagnosis of CAD with MCG. In this study, we examined the validity of the algorithm with the prior probability distribution in diagnosis of new patients admitted to the hospital in 2005. In the results, presence of CAD could be found with sensitivity and specificity of 81.3% and 71.4%, respectively, in patients with chest pain and non-diagnostic ECG findings.
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.
SQUID와 검출코일의 초전도 결합방식이 개선된 1차 권선형 미분계 시스템
이용호,유권규,김진목,권혁찬,김기웅,박용기,Lee, Y.H.,Yu, K.K.,Kim, J.M.,Kwon, H.,Kim, K.,Park, Y.K. 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
In order to have a superconductive connection between the wire-wound pickup coil and input coil, typically Nb terminal blocks with screw holes are used. Since this connection structure occupies large volume, large stray pickup area can be generated which can pickup external noise fields. Thus, SQUID and connection block are shielded inside a superconducting tube, and this SQUID module is located at some distance from the distal coil of the gradiometer to minimize the distortion or imbalance of uniform background field due to the superconducting module. To operate this conventional SQUID module, we need a higher liquid He level, resulting in shorter refill interval. To make the fabrication of gradiometers simpler and refill interval longer, we developed a novel method of connecting the pickup coil into the input coil. Gradiometer coil wound of 0.125-mm diameter NbTi wires were glued close to the input coil pads of SQUID. The superconductive connection was made using an ultrasonic bonding of annealed 0.025-mm diameter Nb wires, bonded directly on the surface of NbTi wires where insulation layer was stripped out. The reliability of the superconductive bonding was good enough to sustain several thermal cycling. The stray pickup area due to this connection structure is about $0.1\;mm^2$, much smaller than the typical stray pickup area using the conventional screw block method. By using this compact connection structure, the position of the SQUID sensor is only about 20-30 mm from the distal coil of the gradiometer. Based on this compact module, we fabricated a magnetocardiography system having 61 first-order axial gradiometers, and measured MCG signals. The gradiometers have a coil diameter of 20 mm, and the baseline is 70 mm. The 61 axial gradiometer bobbins were distributed in a hexagonal lattice structure with a sensor interval of 26 mm, measuring $dB_z/dz$ component of magnetocardiography signals.