• Progress in Superconductivity
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• 제4권1호
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• pp.48-52
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• 2002

When applying a SQUID system for diagnosing heart disease, it is informative to obtain the source current distributions from the measured MCG (magnetocardiogram) signals since the bioelectric activity in the heart is generally represented by distributed current sources. In order to estimate the Primary current distribution in a heart, the minimum norm estimate was computed, assuming a source plane below the chest surface. In the simulation, current distributions, which were computed for the test dipoles represented well the essential feature of the test-current configurations. Source current reconstruction was performed for MCG signal of a healthy volunteer, which was recorded using a 40-channel SQUID system in a magnetically shielded room. It was found that the obtained current distribution is consistent with the electrical activity in a heart.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 추계학술대회
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• pp.11-14
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• 1996

Biomagnetic measurements provide superior spatial and temporal resolutions compared with the present electric measurements. We developed a SQUID system for biomagnetic applications. A magnetic field from the spontaneous ${\tau}$-rhythm activity and an auditory evoked magnetic field have been measured. And a measurement of magnetocardiogram and its field mapping have been done.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.444-447
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• 2004

A heart diagnosis system adopts hundreds of Superconducting Quantum Interface Device(SQUID) sensors for precision MCG(Magnetocardiogram) or MEG(Magnetoencephalogram) signal acquisitions. This system requires correct and real-time data acquisition from the sensors in a required sampling interval, i.e., 1 mili-second. This paper presents our hardware design and test results, to acquire data from 256 channel analog signal with 1-ksample/sec speed, using 12-bit 8-channel ADC devices, SPI interfaces, parallel interfaces, and 8-bit microprocessors. We chose to implement parallel data transfer between microprocessors as an effective way of achieving such data collection. Our result concludes that the data collection can be done in 250 ${\mu}sec$ time-interval.

• 대한기계학회논문집A
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• 제34권2호
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• pp.153-160
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• 2010

인체의 심장 활동에 의해 발생되는 생체 자기 신호를 심자도(magnetocardio-gram, MCG)라고 부른다. 이러한 생체자기장은 극저온 상태에서 고감도 자장센서인 SQUID(Superconducting QUantum Interference Device)를 사용함으로서 측정할 수 있다. 이 심자도 장비의 냉각장치는 액체 헬륨을 냉매로 사용하며 이 냉매를 보관하는 방법이 장비의 성능을 좌우한다. 액체 저온 듀아가 극저온 4 K에서 초전도 특성을 유지하기 위하여 사용된다. 본 연구에서는 액체 헬륨 듀아의 온도분포 특성이 연구되었다. 본 연구에서 사용된 듀아는 액체헬륨 용량이 30 L이고 5일간 유지된다. 듀아에는 150 K와 40 K의 이중 차폐체가 설치되었다. 열차폐체 끝단에서의 온도가 측정되었으며 전산모델의 해석결과와 비교되었다. 기하 설계 변수에 대한 최적화 기법을 적용하여 냉각장치인 저온 듀아의 열전단율을 최소화하였으며 듀아의 응력분포에 영향을 갖는 설계 기하 변수들의 특성을 연구하였다. 냉각장치의 열해석 및 최적화해석을 위해 유한요소 코드 ANSYS 10을 사용하였다. 저온 듀아에 사용된 전산모델은 열복사에 의한 영향을 최소화 할 수 있는 분야에서 온도 분포를 예측하는데 유용하게 사용될 수 있다.

• Progress in Superconductivity
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• 제5권1호
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• pp.55-60
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• 2003

We designed and constructed integrated 3-channel flux-locked-loop (FLL) electronic system for the control and readout of high-T$_{c}$ SQUIDs. This system consists of low noise preamplifiers, integrators, interface circuits, and software. FLL operation was carried out with biased signals of 19 KHz modulated current and 150 KHz modulated flux, which are reconstructed as detected signals by preamplifier and demodulator. Computer controlled interface circuits regulate FLL circuit and adjust SQUID parameters to the optimum operating condition. The software regulates interface circuits to make an auto-tuning for the control of SQUIDs, and displays readout data from FLL circuit. 3-channel SQUID electronic system was assembled with 3 FLL-interface circuit boards and a power supply board in the aluminum case of 56 mm ${\times}$ 53 mm${\times}$ 150 mm. Overall noise of the system was around 150 fT/(equation omitted)Hz when measured in the shielded room, 200 fT/(equation omitted)Hz in a weakly shielded room, respectively.y.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.155-159
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• 2000

YBCO step-edge dc SQUID magnetometers on sapphire substrates have been fabricated. CeO2 buffer layer and YBCO films were deposited in situ on the low angle (${\sim}$35$^{\circ}$) steps formed on the sapphire substrates. Typical 5-${\mu}$m-wide junction has R$_n$ of 5 ${\omega}$ and I$_c$ of 50 ${\mu}$A with large I$_c$R$_n$ product of 250 ${\mu}$V at 77K. According to applied bias current, depth of voltage modulation was changed and maximum voltage was measured 16 ${\mu}$V. Field noise of do SQUID was measured 100${\sim}$300 fT/${\surd}^{Hz}$ in the 1 $^{kHz}$, and about 1.5 pT/${\surd}^{Hz}$ in the 1/f region. For ac bias reversal method, field noise was decreased in the 1/f region. The QRS peak of magnetocardiogram was measured 50 pT in the magnetically shielded room.

• Progress in Superconductivity
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• 제3권2호
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• pp.151-158
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• 2002

We developed a useful SQUID magnetometer for biomagnetic applications, magnetoencepha-logram(MEG) and magnetocardiogram(MCG), etc. The SQUIDs are based on Double Relaxation Oscillation SQUID(DROS). DROS consists of two SQUIDs(signal SQUID and reference SQUID) in series, and a relaxation circuit of an inductor and a resistor. Specially we used single reference junction instead of the reference SQUID. The SQUIDs are based on hysteretic $Nb/AlO_{x}$Nb junctions, fabricated by using a simple four level process. Because DROS magnetometer has large flux-to-voltage transfer coefficient, we can use simple flux-locked loop electronics fur SQUID operation. When the DROS magnetometer was operated inside a magnetically shielded room, its average magnetic field noise was about 3 (equation omitted) at 100 Hz. This noise level is low enough to measure biomagnetic fields. In this paper, we describe noise characteristics of DROS magnetometer, depending on the operation condition . .

• Progress in Superconductivity
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• 제9권1호
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• pp.45-49
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• 2007

We have investigated the optimum combination of the environmental noise condition and type of SQUID pickup coil in order to obtain maximum signal-to-noise ratio (SNR). The measurement probe consists of 1st order gradiometer with pickup coils of 100 mm, 70 mm, and 50 mm baseline length, a 2nd order gradiometer with 50 mm baseline, and a magnetometer. The pickup coils are fabricated by winding Nb wire on a bobbin with 200 mm diameter. Noise and heart signal of a healthy male were measured by various SQUID sensors with different types of pickup coils in various magnetically shielded rooms (MSR), and compared to each other. The shielding factors were found to be 43 dB, 35 dB and 25 dB at 0.1 Hz for MSR-AS, MSR-BS, MSR-CS, respectively. White noises were $3.5\;fT/Hz^{1/2}$, $4.5\;fT/Hz^{1/2}$ and $3\;fT/Hz^{1/2}$ for the 1st order gradiometers, the 2nd order gradiometers, and magnetometer for all MSRs. SNR of the magnetometer was up to 56 dB in MSR-AS, while the 1st order axial gradiometer with 70 mm baseline length was up to 54 dB in MSR-BS. The 2nd order axial gradiometer with 50 mm baseline length of pickup coil was found to be up to 40 dB in MSR-CS.

• 대한의용생체공학회:의공학회지
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• 제28권4호
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• pp.530-538
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• 2007

Magnetocardiography (MCG) is a device to measure the magnetic field from the heart. It is a noninvasive device and takes only few minutes to record magnetocardiogram from a subject. In this study, we compared the difference of MCG data recorded from 56 normal subjects in early twenties (28 males and 28 females, mean $age=21.0{\pm}1.6$ years) and 36 elderly subjects (20 males and 16 females, mean $age=61.9{\pm}6.9$ years) for the analysis of the age and gender difference. A total of 24 parameters used in the analysis were derived from QRS complex, R-wave, T-wave, and ST-T period. As a result, seven parameters including maximum current angle and map angle showed the significant difference (p<0.01 and p<0.05, respectively) between young males and young females. Significant difference (p<0.05) between elderly males and elderly females was found from a parameter, pole distance at T-wave peak. In the comparison of age difference, seven parameters regarding current moment, pole distance, and dynamics showed the significant difference between young and elderly males. Eight parameters also showed significant difference (p<0.05) between two younger and elderly female groups. Results showed that parameters regarding current moment, pole distance, and dynamics might be changed when people get older. In conclusion, gender and age difference should be considered when MCG data are analyzed for certain parameters.

• Journal of Acupuncture Research
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• 제22권5호
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• pp.111-120
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• 2005

Objectives : The aim of this study is to investigate the effect of acupuncture stimulation on the relationship of change in magnetocardiography (MCG). Methods : For this purpose, 30 heart deficiency volunteers were acupunctured at Shinmun (HA7) and Naegwan (PC6) acupoint. Then, we measured and observed the change of frequency parameters in MCG. Results : In the mean frequency, during and after acupuncture treated groups of PC6 were decreased the activity of $f\;_{mean-max}$ compared to the control group. In the median frequency, during the acupuncture treated group of PC6 was decreased the activity of $f\;_{median-max}$ compared to the control group. Conclusion : These results suggested that acupuncture stimulation plays an important role to the activities of MCG.