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

Optimization of a Third-Order Gradiometer for Operation in Unshielded Environments

The optimum geometry of a third-order gradiometer for operation in unshielded environments is discussed. The optimization result depends on the specific signal and noise conditions. The fetal heart is considered as an example of the signal source. We optimized the gradiometer such that the signal-to-noise ratio is maximized in an averaged sense for all relevant environmental noise conditions and distances to the signal source. The resulting design consists of two second-order gradiometers that can be combined to form a third-order gradiometer in noisy environments, whereas a single second-order gradiometer can be used in low-noise environments. The gradiometer can provide the signal-to-noise ratio that allows detection of fetal heart signals in all relevant environmental noise conditions

Medical applications of diamond magnetometry: commercial viability

The sensing of magnetic fields has important applications in medicine, particularly to the sensing of signals in the heart and brain. The fields associated with biomagnetism are exceptionally weak, being many orders of magnitude smaller than the Earth's magnetic field. To measure them requires that we use the most sensitive detection techniques, however, to be commercially viable this must be done at an affordable cost. The current state of the art uses costly SQUID magnetometers, although they will likely be superseded by less costly, but otherwise limited, alkali vapour magnetometers. Here, we discuss the application of diamond magnetometers to medical applications. Diamond magnetometers are robust, solid state devices that work in a broad range of environments, with the potential for sensitivity comparable to the leading technologies.Comment: 10 pages, 1 figur

Fetal Tachyarrhythmia - Part I: Diagnosis

Fetal tachycardia, first recognized in 1930 by Hyman et al1, is a condition occurring in approximately 0.4-0.6% of all pregnancies2. A subset of these cases with more sustained periods of tachycardia is clinically relevant. The necessity of therapeutic intervention in this condition is still a matter of discussion focused on the natural history of the disease. The spectrum of opinions varies from non-intervention3,4,5 based on a number of cases in which the tachycardia subsided spontaneously6, to aggressive pharmacotherapeutic intervention7,8 based on reports of deterioration of the fetal condition ultimately ending in significant neurological morbidity9,10,11, or fetal demise12,13,14. Prenatal treatment through indirect, maternally administered drug therapy seems to be the preference of most centers15,16,17,18,19,20,21. This matter will be discussed further in Fetal Tachyarrhythmia, Part II, Treatment

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

Optical Magnetometer Array for Fetal Magnetocardiography

We describe an array of spin-exchange relaxation free optical magnetometers designed for detection of fetal magnetocardiography (fMCG) signals. The individual magnetometers are configured with a small volume with intense optical pumping, surrounded by a large pump-free region. Spin-polarized atoms that diffuse out of the optical pumping region precess in the ambient magnetic field and are detected by a probe laser. Four such magnetometers, at the corners of a 7 cm square, are configured for gradiometry by feeding back the output of one magnetometer to a field coil to null uniform magnetic field noise at frequencies up to 200 Hz. Using this array, we present the first measurements of fMCG signals using an atomic magnetometer

Эффективная площадь поверхности карт распределения плотности тока

Магнітокардіографія (МКГ) є методикою вимірювання слабких магнітних полів, які виникають в серці під час його функціонування. МКГ може бути виміряна за допомогою надпровідних квантових інтерференційних датчиків (СКВІД), які перетворюють магнітний потік в напругу, і є найбільш чутливими датчиками для виявлення магнетизму. У даній роботі пропонується аналіз карт розподілу щільності струму міокарда. Одержано залежність ефективної площі поверхні від часу для цілих і розділених на 4 частини карт розподілу щільності струму.Magnetocardiography (MCG) is a technique of measuring the weak magnetic fields generated in the heart during its functioning. MCG can be measured using a superconducting quantum interference device (SQUID) sensor that converts magnetic flux to voltage, and is the most sensitive sensor to detect magnetism. In this paper, analysis of myocardium current density distribution maps is proposed. Effective surface area dependence on time for full and divided into 4 parts current density distribution maps is obtained.Магнитокардиография (МКГ) является методикой измерения слабых магнитных полей, создаваемых в сердце во время его функционирования. МКГ может быть измерена с помощью сверхпроводящих квантовых интерференционных датчиков (СКВИД), которые преобразуют магнитный поток в напряжение, и являются наиболее чувствительными датчиками для обнаружения магнетизма. В данной работе предлагается анализ карт распределения плотности тока миокарда. Получена зависимость эффективной площадь поверхности от времени для целых и разделенных на 4 части карт распределения плотности тока

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

Magnetocardiography with a modular spin-exchange relaxation free atomic magnetometer array

We present a portable four-channel atomic magnetometer array operating in the spin exchange relaxation-free regime. The magnetometer array has several design features intended to maximize its suitability for biomagnetic measurement, specifically foetal magnetocardiography, such as a compact modular design, and fibre coupled lasers. The modular design allows the independent positioning and orientation of each magnetometer, in principle allowing for non-planar array geometries. Using this array in a magnetically shielded room, we acquire adult magnetocadiograms. These measurements were taken with a 6-11 fT Hz^(-1/2) single-channel baseline sensitivity that is consistent with the independently measured noise level of the magnetically shielded room.Comment: 15 pages, 5 figure

Multichannel heart scanner based on high-Tc SQUIDs

A 7-channel magnetometer for magnetocardiography based on high-T c SQUIDs has been realized. This magnetometer is used for test experiments in the development of a multichannel high-Tc SQUID based heart-scanner for clinical applications. The intrinsic noise level of the channels in the 7-channel system is typically 120 fT/¿(Hz) down to 1 Hz. Magnetocardiograms were recorded inside a magnetically shielded room. Introductory experiments were performed on the suppression of noise by combining magnetometers to form planar gradiometers. The noise suppression that can be established appeared to be limited by the imbalance of the gradiometric configuration, which is roughly 2%. This relatively poor balance of the system is caused by inaccuracies in the transfer functions of the individual SQUID magnetometers, and by deviations from the planar geometr