64-channel second-order axial gradiometer system based on DROS for magnetocardiogram in a thin shielded room

Lee, Y.H.; Hung, Kam; Kim, J.M.; Kwon, Hyuk Chan; Kim, K.; Park, Y.K.

doi:10.1016/j.physc.2008.05.174

Cited by 14 publications

(4 citation statements)

References 6 publications

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“…The simulated MCG data were based on the KRISSMCG system (Center for Biosignals, Korea Research Institute of Standards and Science, Korea), and the system was consisted of 64-channel double relaxation oscillation superconducting quantum interference devices sensors [27]. The pickup coil was the first-order axial gradiometer type with a baseline of 70 mm, and the noise level of each sensor was approximated to 5 fT rms /Hz 1/2 at 100 Hz.…”

Section: Mcg System and The Cardiac Conductor Modelmentioning

confidence: 99%

Three-Dimensional Reconstruction of a Cardiac Outline by Magnetocardiography

Kim

Lim

et al. 2015

IEEE Trans. Biomed. Eng.

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A 3-D cardiac visualization is significantly helpful toward clinical applications of magnetocardiography (MCG), but the cardiac reconstruction requires a segmentation process using additional image modalities. This paper proposes a 3-D cardiac outline reconstruction method using only MCG measurement data without further imaging techniques. The cardiac outline was reconstructed by a combination of both spatial filtering and coherence mapping method. The strength of cardiac activities was first estimated by the array-gain constraint minimum-norm spatial filter with recursively updated gram matrix (AGMN-RUG). Then, waveforms were reconstructed at whole source grids, and the maximum source points of an atrium and ventricle were selected as a reference, respectively. Next, the coherence between each maximum source point and whole source points was compared by the coherence mapping method. A reconstructed cardiac outline was validated by comparing with an overlapped volume ratio when the reconstructed volume was identically matched with the original volume. The results obtained by the AGMN-RUG were compared to the results by other spatial filters. The accuracy of numerical simulation and phantom experiment by the AGMN-RUG was superior 10% and 8%, respectively, than the accuracy by the standardized low-resolution electromagnetic tomography. This accuracy demonstrated the efficacy of the proposed 3-D cardiac reconstruction method.

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Section: Mcg System and The Cardiac Conductor Modelmentioning

confidence: 99%

Three-Dimensional Reconstruction of a Cardiac Outline by Magnetocardiography

Kim

Lim

et al. 2015

IEEE Trans. Biomed. Eng.

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“…To solve this problem, it is more practical to use SQUID gradiometers in a simple MSR, or even in an unshielded environment. [4][5][6] A gradiometer always consists of a SQUID and a gradiometric pick-up coil, which can suppress background fields from distant sources while retaining substantially high sensitivity to nearby sources. A gradiometric coil is always formed by two or more coils which are coaxially connected in series but set in opposite directions.…”

Section: Introductionmentioning

confidence: 99%

Optimization of pick-up coils for weakly damped SQUID gradiometers

Yang¹,

Wang²,

Kong³

et al. 2018

Chinese Phys. B

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The performance of a superconducting quantum interference device (SQUID) gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupled flux threading a magnetometer obtained by Wikswo, we studied how the gradiometer performance parameters, including the current dipole sensitivity, spatial resolution and signal-to-noise ratio (SNR), are affected by its pick-up coil via MatLab simulation. Depending on the simulation results, the optimal pick-up coil design region for a certain gradiometer can be obtained. To verify the simulation results, we designed and fabricated several first-order gradiometers based on the weakly damped SQUID with different pick-up coils by applying superconducting connection. The experimental measurements were conducted on a simple current dipole in a magnetically shielding room. The measurement results are well in coincidence with the simulation ones, indicating that the simulation model is useful in specific pick-up coil design.

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“…Conventional SQUID systems for biomagnetism are directly cooled by liquid helium. We installed three conventional 152-ch whole-head SQUID magnetoencephalogram (MEG) systems and six SQUID magnetocardiogram (MCG) systems cooled by liquid helium at several hospitals [2,3,[10][11][12]. The MEG and MCG systems consumed more than 4,500 L and 1,500 L of liquid helium per year, respectively.…”

Section: Introductionmentioning

confidence: 99%

Closed-cycle cryocooled SQUID system with superconductive shield for biomagnetism

Hung¹,

Lee²,

Lee³

et al. 2014

Supercond. Sci. Technol.

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We developed a cryocooled SQUID system with which human magnetocardiogram (MCG) and possibly magnetoenceparogram (MEG) can be measured. To reduce cyclic magnetic noises originating from the regenerator of the cold heads of the cryocooler, a superconductive shield (99.5% Pb) was used to protect the SQUID sensors, and a ferromagnetic shield (78% Ni alloy) was used to screen the cold head. In addition, the SQUID sensors' chamber was placed at a distance of 1.8 m from the cold head chamber to install the cold-head chamber outside the magnetically shielded room (MSR) for future development. The loss in cooling power due to the increased distance was compensated by increasing the number of thermal rods, and thus the SQUID sensor and superconductive shield could be refrigerated to 4.8 K and 5 K, respectively. The superconductive shield successfully rejected thermal noise emitted from metallic blocks used to improve thermal conduction. The noise of the SQUID system was 3 fT/Hz 1 2 , and the cyclic magnetic noise could be reduced to 1.7 pT. We could obtain a clear MCG signal while the entire cryogenics was in operation without any special digital processing.

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64-channel second-order axial gradiometer system based on DROS for magnetocardiogram in a thin shielded room

Cited by 14 publications

References 6 publications

Three-Dimensional Reconstruction of a Cardiac Outline by Magnetocardiography

Three-Dimensional Reconstruction of a Cardiac Outline by Magnetocardiography

Optimization of pick-up coils for weakly damped SQUID gradiometers

Closed-cycle cryocooled SQUID system with superconductive shield for biomagnetism

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