Active noise compensation for multichannel magnetocardiography in an unshielded environment

A multichannel high-T/sub c/-SQUID-based heart scanner for unshielded environments is under development, Outside a magnetically shielded room, sensitive SQUID measurements are possible using gradiometers. However, it is difficult to realize large-baseline gradiometers in high-T/sub c/ materials, Therefore, the authors developed two active noise compensation techniques. In the Total Field Compensation technique, a Helmholtz type coil set is placed around the sensors. One magnetometer is used as a zero detector controlling the compensation current through the coil set. For Individual Flux Compensation, the reference signal is sent to the separate SQUIDs (or their flux transformer circuits) to compensate the local environmental noise fluxes, The latter technique was tested on low-T/sub c/ rf-SQUID magnetometers, each sensor set to a field resolution SQUID magnetometers, i.e. 0.1 pT/sub RMS///spl radic/Hz. The authors were able to suppress the environmental disturbances to such an extent that magnetocardiograms could be recorded in an ordinary environment. Here the two suppression techniques are described and experimental results are presente

Prospects for atomic magnetometers employing hollow core optical fibre

Presently, among the most demanding applications for highly sensitive magnetometers are Magnetocardiography (MCG) and Magnetoencephalography (MEG), where sensitivities of around 1pT.Hz<sup>-1/2</sup> and 1fT.Hz<sup>-1/2</sup> are required. Cryogenic Superconducting Quantum Interference Devices (SQUIDs) are currently used as the magnetometers. However, there has been some recent work on replacing these devices with magnetometers based on atomic spectroscopy and operating at room temperature. There are demonstrations of MCG and MEG signals measured using atomic spectroscopy These atomic magnetometers are based on chip-scale microfabricated components. In this paper we discuss the prospects of using photonic crystal optical fibres or hollow core fibres (HCFs) loaded with Rb vapour in atomic magnetometer systems. We also consider new components for magnetometers based on mode-locked semiconductor lasers for measuring magnetic field via coherent population trapping (CPT) in Rb loaded HCFs

Multi-Channel Magnetocardiogardiography System Based on Low-Tc SQUIDs in an Unshielded Environment

AbstractMagnetocardiography (MCG) using superconducting quantum interference devices (SQUIDs) is a new medical diagnostic tool measuring biomagnetic signals that are generated by the electrical activity of the human heart. This technique is completely passive, contactless, and it has an advantage in the early diagnosis of heart diseases. We developed the first unshielded four-channel MCG system based on low-Tc DC SQUIDs in China. Instead of using a costly magnetically shielded room, the environmental noise suppression was realized by using second-order gradiometers and three-axis reference magnetometer. The measured magnetic field resolution of the system is better than 1 pT, and multi-cycle human heart signals can be recorded directly. Also, with the infrared positioning system, 48 points data collection can be realized by moving the non-magnetic bed nine times

Hybrid GMR Sensor Detecting 950 pT/sqrt(Hz) at 1 Hz and Room Temperature.

Advances in the magnetic sensing technology have been driven by the increasing demand for the capability of measuring ultrasensitive magnetic fields. Among other emerging applications, the detection of magnetic fields in the picotesla range is crucial for biomedical applications. In this work Picosense reports a millimeter-scale, low-power hybrid magnetoresistive-piezoelectric magnetometer with subnanotesla sensitivity at low frequency. Through an innovative noise-cancelation mechanism, the 1/f noise in the MR sensors is surpassed by the mechanical modulation of the external magnetic fields in the high frequency regime. A modulation efficiency of 13% was obtained enabling a final device's sensitivity of ~950 pT/Hz1/2 at 1 Hz. This hybrid device proved to be capable of measuring biomagnetic signals generated in the heart in an unshielded environment. This result paves the way for the development of a portable, contactless, low-cost and low-power magnetocardiography device

Методы анализа данных, полученных с помощью магнитокардиографии

Неінвазивна діагностика серцево-судинних захворювань є однією з найважливіших завдань сучасної кардіології. Важливе місце серед методів діагностики займає магнітокардіографія (МКГ) – метод неінвазивного електрофізіологічного дослідження серця, що полягає в безконтактній реєстрації та аналізі магнітного поля, породженого електричною активністю міокарда протягом серцевого циклу. У роботі розглянуто основні способи представлення МКГ-даних, їх переваги і недоліки. Надано огляд існуючих методів аналізу даних, отриманих з допомогою МКГ, у тому числі карт розподілу густини струму, подані їх переваги та обмеження, а також визначено актуальні напрями подальших досліджень щодо розвитку техніки аналізу МКГ.Non-invasive diagnosis of cardiovascular diseases is one of the most important problems of modern cardiology. Important place among diagnostic methods takes Magnetocardiography (MCG) - method of noninvasive electrophysiological study of heart that provides contactless registration and analysis of magnetic fields generated by electrical activity of the myocardium during cardiac cycle over the human chest. The paper discusses the main ways of representing MCGdata, their advantages and disadvantages. Also in our work the overview of existing methods of analysis of MCGdata, including current density distribution maps is given, and the directions for further research are defined.Неинвазивная диагностика сердечно-сосудистых заболеваний является одной из важнейших задач современной кардиологии. Важное место среди методов диагностики занимает магнито-кардиография (МКГ) метод неинвазивного электрофизиологического исследования сердца, заключается в бесконтактной регистрации и анализе над грудной клеткой человека магнитного поля, порожденного электрической активностью миокарда в течение сердечного цикла. В работе рассмотрены основные способы представления МКГ-данных, их преимущества и недостатки. Кроме того, в работе дан обзор существующих методов анализа данных, полученных с помощью МКГ, в том числе карт распределения плотности тока, а также указано направление дальнейшей работы над проблемой

A reference dataset for verifying numerical electrophysiological heart models

<p>Abstract</p> <p>Background</p> <p>The evaluation, verification and comparison of different numerical heart models are difficult without a commonly available database that could be utilized as a reference. Our aim was to compile an exemplary dataset.</p> <p>Methods</p> <p>The following methods were employed: Magnetic Resonance Imaging (MRI) of heart and torso, Body Surface Potential Maps (BSPM) and MagnetoCardioGraphy (MCG) maps. The latter were recorded simultaneously from the same individuals a few hours after the MRI sessions.</p> <p>Results</p> <p>A training dataset is made publicly available; datasets for blind testing will remain undisclosed.</p> <p>Conclusions</p> <p>While the MRI data may provide a common input that can be applied to different numerical heart models, the verification and comparison of different models can be performed by comparing the measured biosignals with forward calculated signals from the models.</p

A room temperature 19-channel magnetic field mapping device for cardiac signals

We present a multichannel cardiac magnetic field imaging system built in Fribourg from optical double-resonance Cs vapor magnetometers. It consists of 25 individual sensors designed to record magnetic field maps of the beating human heart by simultaneous measurements on a grid of 19 points over the chest. The system is operated as an array of second order gradiometers using sophisticated digitally controlled feedback loops.Comment: 3 pages, 3 figures, submitted to Applied Physics Letter

Assessment of Fetal Autonomic Nervous System Activity by Fetal Magnetocardiography: Comparison of Normal Pregnancy and Intrauterine Growth Restriction

Objective. To clarify the developmental activity of the autonomic nervous system (ANS) of the normal fetus and intrauterine growth restriction (IUGR) cases using fetal magnetocardiography (FMCG). Subjects and Methods. Normal pregnancy (n = 35) and IUGR (n = 12) cases at 28–39 and 32–37 weeks of gestation, respectively, were included in this study. The R-R interval variability was used to calculate the coefficient of variance (CVRR) and low frequency/high frequency (LF/HF) ratio. Results. The value of CVRR in the normal pregnancy group displayed a slight increasing trend with gestational age. However, no such trend was observed in the IUGR group. In contrast, the LF/HF ratio in both the normal pregnancy group and the IUGR group clearly increased over the gestational period; the normal group showing statistical significance. Conclusion. The development of fetal ANS activity in IUGR cases might differ from that observed in the normal pregnancy group, and this may facilitate early detection of IUGR