Magnetocardiographic System Research Articles

Optimization of low-pass filters in a flux transformer of a SQUID magnetometer for MCG studies

Research and optimization of a passive low-pass filter (LPF) for a magnetic flux transformer of superconducting quantum interferometric detector (SQUID) operating in a magnetocardiographic (MCG) system, in an unshielded room, under the influence of electromagnetic interference of significant intensity have been carried out. The amplitude-frequency characteristics (AFC) of the LPF in the SQUID magnetic flux transformer are calculated for various shunt circuits, including the LPF circuit recommended by “Supracon” group for its CE2 blue model of the SQUID. The analysis of LPF circuits and their frequency response are carried out in order to ensure maximum protection of the input circuits of the SQUID from the effects of electromagnetic interference. It is shown that the optimal LPF for the MCG system is a filter with an active resistance of about 1 Ω in the shunt circuit of magnetic flux transformer. The performed calculations of the LPF intrinsic noise in the SQUID magnetic flux transformer showed that the additional noise of the shunt circuit with a 1 Ω resistor is significantly less than external noise for MCG system operating in unshielded rooms in the industrial city.

Predictive value of the complex magnetocardiographic index in patients with intermediate pretest probability of chronic coronary artery disease

The aim of this paper is to investigate the predictive value of the new integrated magnetocardiographic (MCG) index (CI) in the diagnosis of coronary artery disease (CAD) in patients with suspected CAD with intermediate pretest probability of the disease and uninformative results of routine tests. The study was carried out in the Clinic of Cardiology of the Main Military Clinical Hospital of Ukraine, Kiev (clinic 1), and in the Second Medical Clinic of the 'Katholisches Klinikum Essen', Germany (clinic 2).The main group (group 1) included 89 patients without a history of myocardial infarction. Coronary angiography was performed because of chest pain. Depending on the results of coronary angiography, this group was divided into two subgroups: (i) those with at least 70% stenosis in at least one of the main coronary arteries (subgroup 1a) and (ii) those without hemodynamically significant stenosis (subgroup 1b). The control group included 43 healthy volunteers.In all participants, the MCG examination was performed using a seven-channel MCG system located in an unshielded room. An integrated MCG index (CI), consisting of six parameters, was calculated. It can be shown that CI was significantly higher in patients with stenosis 70% or more compared with the patients without stenosis and healthy volunteers. Sensitivity was 93%, specificity was 84%, positive predictive value was 85%, and negative predictive value was 93%. The MCG test at rest has the potential to be useful in the noninvasive diagnosis of CAD in patients with intermediate pretest probability of disease and uninformative results of routine tests.

Usefulness of Magnetocardiogram to Detect Unstable Angina Pectoris and Non-ST Elevation Myocardial Infarction

Electrophysiologic information as well as anatomic information to detect coronary artery disease is important for accurate diagnosis. A diagnostic tool that can detect patients with unstable angina pectoris (UAP) or non-ST elevation myocardial infarction (NSTEMI) with severe stenosis would be beneficial for patients and clinicians. Magnetocardiography has been recognized as a noncontact, noninvasive, fast tool to detect ischemic coronary artery disease and provide direct electrophysiologic information from the heart. In this study, 10 magnetocardiographic (MCG) parameters from 4 groups, including 185 young controls, 19 age-matched controls (AMCs), 110 patients with UAP, and 83 patients with NSTEMIs, were analyzed. A 64-channel MCG system in a magnetically shielded room was used. All 10 parameters showed significant differences (p <0.001) between controls and patients with NSTEMIs, and 6 parameters showed significant differences (p <0.01) between AMCs and patients with UAP. MCG parameters significantly increased when ischemic heart conditions worsened. Of the 10 parameters, the magnetic field map was among the easiest ways to detect the severity of coronary artery disease. Abnormal magnetic field maps were observed frequently with worsening ischemic coronary artery disease (70% of patients with UAP and 92.5% of those with NSTEMIs had abnormal maps). The combination of the binary boundaries of the 10 parameters had 96.4% sensitivity and 85% specificity to detect NSTEMI. In conclusion, the MCG parameters and magnetic field maps may detect UAP and NSTEMI easily when they are considered together.

Development of a 6-Channel High-$T_{\rm C}$ SQUID Magnetocardiograph System

We have developed a new type of magnetocardiograph (MCG) system employing 6 high-TC SQUID magnetometers. We have fabricated high performance YBCO SQUID devices for the system. The lightweight MCG system, requiring liquid nitrogen as a coolant, consists of 6-channel SQUID sensors and an adjustable patient bed with sliding motion. The MCG system showed stable operation in a room with moderate magnetic shielding. In normal operation with a moving subject, we could obtain 36-point and 48-point MCG mappings with high enough signal qualities for clinical trials.

Performance of open cylindrical magnetic shield for magnetocardiograph using low-Tc SQUIDs

We evaluated the performance of an open cylindrical magnetic shield for a magnetocardiograph using low-transition temperature (low-Tc) superconducting quantum interference devices (SQUIDs) so that we could miniaturize an entire magnetocardiograph system. The open magnetic shield was about 1 m in diameter and 2 m in axial length, and had a revolving door that provided easy access inside the shield as well as easy operation. The shielding factor for our magnetic shield was above 46 dB, and its distribution was uniform in the vicinity of the shield. The magnetocardiogram including the P-wave peak could clearly be measured with 64 axial gradiometers based on low-Tc SQUIDs in the open magnetic shield. Typical distributions of myocardial ion currents of a normal subject were also obtained with the system.

Development of high-throughput fabrication process of HTS SQUID for 51-ch MCG system

A high-throughput high-Tc SQUID fabrication process that can provide the appropriate number of SQUIDs for a 51-channel magnetocardiograph (MCG) has been developed. A new deposition system—based on a pulsed-laser-deposition technique to increase the process throughput in fabricating superconducting YBa2Cu3Oy thin films—was developed. In this system, nine superconducting thin films are successively deposited on bicrystal substrates in one deposition sequence. A mask aligner, which was customized for the bicrystal substrate, was also developed. This system enables mask alignment for the bicrystal grain boundary without the need for preprocessing to visualize it. In addition, the magnetometer pattern was designed to improve the yield for magnetometer fabrication. In this directly coupled magnetometer, four SQUIDs were connected with the same pickup coil. Accordingly, the yield of magnetometer could be enhanced by selecting the best SQUID among the four.

Basic Technology and Clinical Application Technique of Magnetocardiograph

The Magnetocardiograph (MCG) is a new non-invasive tool for diagnosing the heart disease. MCG has a potential to detect a ischemia and arrhythmic focus accurately. In this article, we introduce the basic technology of MCG system and clinical application technique.

Wavelet transformation for magnetocardiography signal

How to extract the magnetocardiographic (MCG) signals from the noisy background is the key of MCG signal processing. In this paper, wavelet transformation is adopted to recover the MCG signals, acquired by using the high Tcc dc -SQUI D magnetometer developed at our institute. The results of this work show that t his method is much more effective than other methods used before and can be implemented in the MCG system for routing operation. This method can also be used in noise cancellation of other non-stationary signals.

Multichannel mapping of fetal magnetocardiogram in an unshielded hospital setting

To evaluate the feasibility of unshielded in-hospital multichannel mapping of fetal magnetocardiogram (FMCG), with a 36-channel system for standard adult magnetocardiographic (MCG) recordings, and its reliability according to the recommended standards for FMCG. FMCG was ambulatory mapped with a 36-channel MCG system, in six normal pregnancies at different gestational ages. MCG analysis included adaptive digital filtering of 50 Hz, signal averaging, reconstruction of magnetic field distribution (MFD) and source localization. Fixed Point Independent Component Analysis algorithm (FastICA) was used to reconstruct the FMCG, separating them from maternal contamination and noise. The quality of FMCG recorded after the 32nd gestational week and reconstructed with FastICA was close to FMCG obtained in shielded rooms, and good enough to measure cardiac intervals and heart rate variability parameters. In two cases, reconstruction of the MFD during the QRS allowed three-dimensional localization of ventricular sources. A first demonstration has been given that multichannel mapping of FMCG can be performed in unshielded clinical environments, with resolution good enough for contactless assessment of fetal cardiac electrophysiology. FastICA processing on unshielded FMCG, recorded after the 32nd week, provided beat-to-beat analysis and heart rate variability assessment. Further work is needed to improve signal reconstruction in early pregnancy.

A Mobile and Space-saving High-temperature Superconducting Multichannel Magnetocardiograph in a Vertical Magnetically Shielded Cylinder

A high-temperature superconducting (HTS) magnetocardiographic system composed of 16-channels HTS-Superconducting Quantum Interference Device (SQUID) magnetometers and a vertical magnetically shielded cylinder has been developed. The cylinder is designed to save space and provide mobility for the entire system, including the magnetically shielded cylinder. It consists of two fixed semicircular shells and a sliding semicircular door, all of which are made from sheets of a flexible nanocrystalline soft-magnetic material. The cardiomagnetic field from a subject seated in the vertical magnetically shielded cylinder is measured by multichannel HTS-SQUID magnetometers that are sensitive to field strengths weaker than 100 fT/(Hz)1/2. The high signal-to-noise ratio of the magnetometer signals makes beat-to-beat measurement of the cardiomagnetic field possible. This HTS-based multichannel MCG system is being applied to medical applications such as the detection of arrhythmias and ischemic heart disease.

HTS SQUID gradiometer using substrate resonators operating in an unshielded environment - A portable MCG system

We have demonstrated and verified the basic feasibility of performing magnetocardiographic (MCG) measurements without magnetic shielding when using a first-order electronic gradiometer with our novel dielectric substrate resonator rf SQUIDs. The setup at the operation site involved adjustment of the gradiometer's baseline length and adaptive balancing. Our experimental portable system was tested in three environments differing in the level of electromagnetic interference.

Magnetocardiography —State of the art

Electrophysiologic information as well as anatomic information to detect coronary artery disease is important for accurate diagnosis. A diagnostic tool that can detect patients with unstable angina pectoris (UAP) or non–ST elevation myocardial infarction (NSTEMI) with severe stenosis would be beneficial for patients and clinicians. Magnetocardiography has been recognized as a noncontact, noninvasive, fast tool to detect ischemic coronary artery disease and provide direct electrophysiologic information from the heart. In this study, 10 magnetocardiographic (MCG) parameters from 4 groups, including 185 young controls, 19 age-matched controls (AMCs), 110 patients with UAP, and 83 patients with NSTEMIs, were analyzed. A 64-channel MCG system in a magnetically shielded room was used. All 10 parameters showed significant differences (p <0.001) between controls and patients with NSTEMIs, and 6 parameters showed significant differences (p <0.01) between AMCs and patients with UAP. MCG parameters significantly increased when ischemic heart conditions worsened. Of the 10 parameters, the magnetic field map was among the easiest ways to detect the severity of coronary artery disease. Abnormal magnetic field maps were observed frequently with worsening ischemic coronary artery disease (70% of patients with UAP and 92.5% of those with NSTEMIs had abnormal maps). The combination of the binary boundaries of the 10 parameters had 96.4% sensitivity and 85% specificity to detect NSTEMI. In conclusion, the MCG parameters and magnetic field maps may detect UAP and NSTEMI easily when they are considered together.