Biomagnetic Fields Research Articles

The Sixth Sense-Emotional Contagion; Review of Biophysical Mechanisms Influencing Information Transfer in Groups

Rioting historically has been known to cause changes in individual cognition, with heightened emotionality, increased excitement and reduced reflective thought. A cross-disciplinary literature review hypothesises emotional states generate corresponding metabolic bio magnetic fields that radiate in patterns reflecting these emotional states. The oscillatory phase of these waves is advanced as being more significant than the power of signal, permitting stochastic effects to magnify signals by appropriating ambient noise. Possible transmission and detection structures in the body are discussed, induced paramagnetic sensitivity in crowd participants in a phase transition process is hypothesised, the effect may be proportional to crowd numbers. It is suspected that positive effects seen in Transcranial Magnetic Therapy used to treat depression may be operating on this mechanism, acting on natural receptors in the limbic system which also capture light and are implicated in mood transitions. A number of paramagnetic neurotransmitters may be implicated.

P 208 A K-Rb hybrid Optically Pumped Atomic Magnetometer toward Ultra-low field Multimodal MRI Systems

To contribute for improvement of longevity and quality of human life, we have been developing optically pumped atomic magnetometers (OPAMs) to measure tiny biomagnetic fields and MRIs. In recent years, OPAMs have reached sensitivities comparable to and even surpassing those of magnetometers based on super-conducting quantum interference devices (SQUIDs) [1] . In addition, OPAMs have the intrinsic advantage of not requiring cryogenic cooling. Meanwhile, MRI is one of the most useful diagnostic imaging modalities, which enables visualization of the anatomy and function of the human. However, the conventional high magnetic field scanner has some limitations such as high cost and risk for patients with metal implants. To acquire MRIs without these limitations, ultra-low filed (ULF) MRI systems attracted attention in recent years. We have developed an OPAM using a hybrid cell of K and Rb atoms [2] toward ULF multimodal MRI systems. The objective of this study is to investigate the optimal properties of the OPAM theoretically comparing with experiment results. The sensor head of the OPAM used in this study was a cubic Pyrex glass cell, whose size was 3 x 3 x 3 cm 3 and within which K and Rb atoms were enclosed with He and N 2 as buffer gases at a ratio of 10 to 1 and at a total pressure of 150 kPa at room temperature. The Rb atoms were spin-polarized by a circularly-polarized pump beam and the spin polarization was transferred to the K atoms by spin exchange collisions. The spin polarization rotated around the external magnetic field orthogonal to both the pump and probe beams. Here, the plane of a linearly-polarized probe beam penetrating the group of spin-polarized atoms is rotated by Faraday effect. We applied a 100 Hz sinusoidal magnetic field of 48 pT as a test signal and examined sensitivities of the OPAM We theoretically investigated the properties of the hybrid OPAM and considered the adequacy of the properties comparing with experiment results. We have found that the experimental results agree well with the theoretical values. The optimum density ratio of K and Rb atoms was expected to be 10-100 for more sensitive magnetometers. We could measure of human magnetocardiograms (MCGs) and plan to measure MR signals using the hybrid OPAM. We developed a K-Rb hybrid OPAM and examined its sensitivities. Results shown in this study demonstrate the feasibility of the OPAM as a magnetic sensor toward ULF multimodal MRI systems. This work is partly supported by Grant-in-Aid for Researches (No. 24240081 & 24650221) and the Innovative Techno-Hub for Integrated Medical Bio-imaging of the Project for Developing Innovation Systems, from MEXT, Japan.

Magnetic sensors using amorphous metal materials: detection of premature ventricular magnetic waves

The detection of magnetic activity enables noncontact and noninvasive evaluation of electrical activity in humans. We review the detection of biomagnetic fields using amorphous metal wire-based magnetic sensors with the sensitivity of a pico-Tesla (pT) level. We measured magnetic fields close to the thoracic wall in a healthy subject sitting on a chair. The magnetic sensor head was mounted perpendicularly against the thoracic wall. Simultaneous measurements with ECG showed that changes in the magnetic field were synchronized with the cardiac electric activity, and that the magnetic wave pattern changed reflecting electrical activity of the atrium and ventricle, despite a large variation. Furthermore, magnetic waves reflecting ventricular arrhythmia were recorded in the same healthy subject. These results suggest that this magnetic sensor technology is applicable to human physiology and pathophysiology research. We also discuss future applications of amorphous wire-based magnetic sensors as well as possible improvements.

Water-Soluble and Biocompatible MnO@PVP Nanoparticles for MR Imaging <I>In Vitro</I> and <I>In Vivo</I>

The uniform-sized manganese oxide nanoparticles (the oleic-capped MnO NPs) were synthesized by the thermal decomposition of Mn-oleate complex and were transferred into water with the help of cationic surfactant of cetyltrimethyl ammonium bromide (CTAB), then the poly(vinylpyrrolidone) (PVP) membrane was further coated on to them with the aid of anionic dispersant of poly(styrenesulfonate) (PSS) by layer-by-layer electrostatic assembly to render them water soluble and biocompatible. They were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and MTT assay. In vitro cellular uptake test revealed the MnO@PVP NPs were low cytotoxic, biocompatible and could be used as a T,-positive contrast agent for passive targeting magnetic resonance imaging (MRI). Interestingly, signal enhancement in cerebral spinal fluid (CSF) spaces in vivo experiment suggested that the MnO@PVP NPs can pass through the blood brain barrier (BBB). These results show that MnO@PVP NPs are good candidates as MRI contrast agents with the lack of cytotoxicity and have great potential applications in magnetic nano-device and biomagnetic field.

Giant Faraday Rotation in Mesogenic Organic Molecules

Faraday rotation, the rotation of the polarization of light due to a magnetic field in the direction of propagation of the light, is used in applications ranging from quantum memory to the detection of biomagnetic fields. For these applications large Faraday rotation is necessary, but absorption of light is detrimental. In search of these properties, we have characterized the Verdet constant of a so far unexplored class of mesogenic organic molecules. We report their spectra and provide an interpretation. A Verdet constant of almost 2.5 × 105 deg T–1 m–1 is found around 520 nm. This Verdet constant is 3 orders of magnitude larger than the largest known for organic molecules in a region without spectral features. We attribute this enormous Faraday rotation to resonant enhancement by a triplet excitation that does not appear in the linear absorption spectrum and to near-resonant enhancement by low-energy singlet excitations. Furthermore we are able to switch the Faraday rotation by changing the liquid cryst...

Physiological Magnetic Stimulation for Arousal of Elderly Car Driver Evaluated With Electro-Encephalogram and Spine Magnetic Field

Reliable evaluation for the arousal effect of magnetized olivine-crushed-stone-crammed vinyl pipe set on an elderly car driver's spine has been carried out measuring a four-points electroencephalogram using driving simulators considering a defined arousal index β/(δ+θ) . A sintered-magnetized-spherical-particles-crammed pipe is developed for realization of periodically pulse distributed surface magnetic field train matching with the magneto-protonics principle. Transition of the magnetic field time series generated from the spine with application of the physiological magnetic stimulation have also been measured using the amorphous wire and CMOS IC based pico-Tesla resolution magneto-impedance sensor, in which existence of alternative areas of cooperativeness and anti-cooperativeness for transition of the arousal index each other along the spine length direction is suggested. A special point on the central spine generating a large bio magnetic field of around 10 nT amplitude as well as corresponding pit of the stomach position was found.

Magnetic Field Vector Detection in Frequency Domain with an Optically Pumped Atomic Magnetometer

The motion of spin polarization in a high-sensitivity optically pumped atomic magnetometer is described by the Bloch equation. We propose a magnetometer having two nonparallel probe beams to measure both the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> components of spin polarization, while a pumping beam propagates in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> direction. When a bias magnetic field is applied parallel to the pumping beam, the magnetic fields <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bx</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">By</i> both affect the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> components of the spin polarization. The relation between the magnetic field and the magnetometer signal is correctly expressed in matrix form for a simple oscillating magnetic field. The relation enables us to solve the Bloch equation in the frequency domain and retrieve the original waveform of the time-dependent magnetic field waveform. This magnetometer also compensates for distortion of the waveform caused by the resonant nature of the Bloch equation. The magnetic field signal recovery is demonstrated by numerical simulation and the preferred parameter range for the proposed dual-probe magnetometer is shown. As a result, the proposed magnetometer will expand the possibility for weak magnetic field measurements, including biomagnetic fields.

Human MCG measurements with a high-sensitivity potassium atomic magnetometer

Measuring biomagnetic fields, such as magnetocardiograms (MCGs), is important for investigating biological functions. To address to this need, we developed an optically pumped atomic magnetometer. In this study, human MCGs were acquired using a potassium atomic magnetometer without any modulating systems. The sensitivity of the magnetometer is comparable to that of high-Tc superconducting quantum interference devices (SQUIDs) and is sufficient for acquiring human MCGs. The activity of a human heart estimated from the MCG maps agrees well with that measured with SQUID magnetometers. Thus, our magnetometer produces reliable results, which demonstrate the potential of our atomic magnetometer for biomagnetic measurements.

Reconstruction of quasi-radial dipolar activity using three-component magnetic field measurements

ObjectiveWhile standard magnetoencephalographic systems record only one component of the biomagnetic field, novel vector-biomagnetometers enable measurement of all three components of the field at each sensing point. Because information content in standard one-component magnetoencephalography (MEG) is often not adequate to reconstruct quasi-radial dipolar activity, we tested the hypothesis that quasi-radial activity can be estimated using three-component MEG. MethodsWe stimulated the right median nerve in 11 healthy volunteers and recorded the somatosensory evoked fields over the contralateral hemisphere using a novel vector-biomagnetometer system comprised of SQUID-based magnetometer triplets. Source reconstruction for the early cortical components N20m and P25m was subsequently performed. ResultsBoth tangential and quasi-radial dipolar activity could be reconstructed in 10 of the 11 participants. Dipole locations were found in the vicinity of the central sulcus, and dipole orientations were predominantly tangential for N20m and quasi-radial for P25m. The mean location difference between the tangential and quasi-radial dipoles was 11.9mm and the mean orientation difference was 97.5°. ConclusionsQuasi-radial dipolar activity can be reconstructed from three-component magnetoencephalographic measurements. SignificanceThree-component MEG provides higher information content than does standard MEG.

Diamond Sensors for Intracellular Processes, Protein Motion and Biomagnetic Fields

Due to their low cytotoxicity, high photostability and simultaneously small size color center doped diamond nanocrystals promise to be versatile bio labels [1]. In additions they are robust donors for FRET processes and allow for detection of pH changes [2]. Since some color centers are paramagnetic they are even efficient sensors for small electric and magnetic field. This for example might allow for the detection of weak currents caused by the ion flow through individual channels [3]. The talk will summarize recent advances and provide examples for biosensing application of diamond defects [4].[1] J. Wrachtrup, F. Neugart, A. Zappe, F. Jelezko, C. Tietz, J. P. Boudou, A. Krueger, Nano Lett 2007, 7, 3588-3591.[2] J. Wrachtrup, J. Tisler, G. Balasubramanian, B. Naydenov, R. Kolesov, B. Grotz, R. Reuter, J. P. Boudou, P. A. Curmi, M. Sennour, A. Thorel, M. Borsch, K. Aulenbacher, R. Erdmann, P. R. Hemmer, F. Jelezko, Acs Nano 2009, 3, 1959-1965.[3] L. T. Hall, C. D. Hill, J. H. Cole, B. Stadler, F. Caruso, P. Mulvaney, J. Wrachtrup, L. C. L. Hollenberg, P Natl Acad Sci USA 2010, 107, 18777-18782.[4] L. C. L. Hollenberg, L. P. McGuinness, Y. Yan, A. Stacey, D. A. Simpson, L. T. Hall, D. Maclaurin, S. Prawer, P. Mulvaney, J. Wrachtrup, F. Caruso, R. E. Scholten, Nat Nanotechnol 2011, 6, 358-363.

Diffusion in annealing of nanocrystalline Ni&lt;SUB align="right"&gt;80Fe&lt;SUB align="right"&gt;20/Cu composite wires

Weak magnetic field sensors have always been an area of great interest due to their immense potential applications in a wide array of fields such as magnetic anomaly detectors (MAD) in defence-related industry or bio-magnetic field sensors in biomedical industry. The performance of such sensors greatly depends on the magnetic softness of the sensing elements. Thus, optimisation of the post-heat treatment process is crucial as it serves to release stresses induced during the deposition process. In this study, furnace annealing was carried out on Ni

Integration of a Cryocooler into a SQUID Magnetospinography System for Reduction of Liquid Helium Consumption

We are currently developing a magnetospinography (MSG) system for noninvasive functional imaging of the spinal cord. The MSG system is a device for observing a weak magnetic field accompanied by the neural activity of the spinal cord by using an array of low-temperature superconducting quantum interference device (SQUID) magnetic flux sensors. As in the case of other biomagnetic measurement systems such as the magnetoencephalography (MEG) system, the running cost of the MSG system is mainly dependent on the liquid helium (LHe) consumption of a dewar vessel. We integrated a cryocooler into the MSG system to reduce LHe consumption. A pulse tube cryocooler with a cooling power of 0.5Wat 4 K was placed adjacent to a magnetically shielded room and was directly connected to the thermal radiation shield of the dewar by an electrically isolated transfer tube. Cold helium gas was circulated between the cryocooler and the radiation shield. Consequently, the temperature of the radiation shield decreased below 40 K. Previous studies have shown that the detection of a weak magnetic field is often hindered by severe low-frequency band noise from the cryocooler. However, the band of the MSG signals is much higher than that of the cryocooler noise. Therefore, the noise can be filtered out and has a less detrimental effect on MSG measurement than on other biomagnetic field measurements such as MEG measurement. As a result, LHe consumption was reduced by 46%, with no increase in the noise floor.

Magnetic Field Mapping and Biaxial Vector Operation for Biomagnetic Applications Using High-Sensitivity Optically Pumped Atomic Magnetometers

Optically pumped alkali-metal atomic magnetometers are expected to be used not only for biomagnetic field measurements but also for magnetic resonance imaging because of their potential ultrahigh sensitivity. Here, we studied magnetic field mapping and biaxial vector operation using atomic magnetometers. A potassium atomic magnetometer was used in these measurements. First, we obtained sensor output signals by solving the Bloch equation. Next, we measured magnetic field distributions generated by a current dipole electrode that was placed in a spherical phantom, which simulated a group of simultaneously activated neurons in the human brain. We obtained vector contour maps of the magnetic field distributions from the dipoles oriented parallel and orthogonal to the pump laser beam and have found good agreement with theoretical magnetic field distributions. These results demonstrate practical applications of magnetic field mapping and biaxial vector operation using optically pumped atomic magnetometers.

Measurement of Spontaneous Oscillatory Magnetic Field of Guinea-Pig Smooth Muscle Preparation Using Pico-Tesla Resolution Amorphous Wire Magneto-Impedance Sensor

New measured results of spontaneous oscillatory bio-magnetic field generated from preparations of guinea-pig smooth muscle tissue are presented in this paper using the pico-Tesla MI sensor. It is confirmed that the changes in the bio-magnetic field activity precisely synchronized with extracellular electric activity for stomach musculature of the guinea-pig. It is, however, noteworthy that these two activities provide different biological information. A phase lag of around 2 s of the magnetic signal pulse against the extracellular electric signal pulse is newly found. It is also shown that Ca2+ channel activity of the smooth muscle tissue (taenia caeci) can be evaluated using the MI sensor. Both electric and magnetic activities depend on the functionality of the living tissues. Therefore, the pico-Tesla MI sensor has the potential for non-invasive detection use in wide range of biology and medicine, including non-invasive evaluation use of the stem cells development.

Noise Performance of Magnetometers With Resonant Thin-Film Magnetoelectric Sensors

Sensors based on materials with a giant magnetoelectric (ME) effect may be used to measure biomagnetic fields at room temperature. It is necessary to know the noise behavior of the whole detection unit. The noise level of a thin-film ME sensor was measured at room temperature, and suitable types of low-noise amplifiers were investigated. Noise measurements were carried out at room temperature. Results show a sensitivity value of 5.4 pT/ √Hz at a resonance frequency of 330 Hz. Furthermore, the signal-to-noise ratio was investigated in order to improve the sensitivity of the sensor.

Pulse-driven magnetoimpedance sensor detection of biomagnetic fields in musculatures with spontaneous electric activity

We measured biomagnetic fields in musculatures with spontaneous electric activity using a pulse-driven magnetoimpedance (PMI) sensor with the sensitivity improved toward a pico-Tesla (pT) level. Due to the sufficiently short operation interval of 1 μs, this magnetic sensor enabled quasi-real time recordings of the magnetic field for biological electric activity. Isolated small musculatures from the guinea-pig stomach, taenia caeci, portal vein and urinary bladder were incubated in an organ bath at a body temperature. The improved PMI sensor mounted approximately 1 mm below the preparations detected oscillatory magnetic fields reflecting spontaneous electric activities of musculature preparations. In the taenia caeci, application of tetraethyl ammonium (TEA), a K + channel blocker, significantly enhanced the magnetic activity estimated by histogram analysis. Also, in some musculature preparations, simultaneous measurements with electric activity revealed that the observed magnetic activities were attributed to biological electric activity. PMI technology is promising for applications in biology and medicine.

Discrimination of Multiple Sources of 3D Biomagnetic Field using Frequency and Phase Analyses

This paper describes the usefulness of 3D biomagnetic field measurements for discriminating multiple sources closely located and overlapped in time such as in magnetocardiogram(MCG) and magnetoencephalogram (MEG), using frequency and phase analysis. 3D MCG measurements with 48 positions on the chest wall were carried out on normal subjects and on a patient with Wolff-Parkinson-White (WPW) syndrome using a 3D vector second-order gradiometer connected to 39-channel SQUIDs, which can simultaneously detect magnetic fields perpendicular (Bz) and tangential (Bx, By) to the chest wall. To discriminate multiple sources activating in the heart we developed a signal processing method consisting of singular value decomposition(SVD) to estimate the number of equivalent sources, time-frequency analysis to calculate the frequency spectrum of 3D MCG wave-forms, and coherency analysis to calculate phase coherency at each measurement position. We were able to discriminate multiple sources consisting of the source of an accessory pathway and the source of a normal pathway hidden by an intense signal such as the delta wave of the WPW patient, using coherency analysis with the tangential component (Bx, By) added to the normal component(Bz).

Development of a Highly Sensitive Optically Pumped Atomic Magnetometer for Biomagnetic Field Measurements: A Phantom Study

We developed a highly sensitive optically pumped atomic magnetometer for measuring biomagnetic fields from the human body noninvasively. The sensor head was a cubic Pyrex glass cell containing potassium metal and buffer gases. A pump laser beam for spin-polarizing potassium atoms and a probe laser beam for detecting magneto-optical rotation crossed at right angles in the cell, which was heated in an oven to vaporize potassium atoms. The sensitivity of the magnetometer reached to 10-100 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at frequencies below several hundred hertz. To test system performance, we made a phantom which models the human brain, taking into account the contribution of distributed electric currents. First, we tested the phantom by a 306-channel whole-head MEG system and confirmed good agreement of the measured field distributions with theoretical calculations. Subsequently, we measured magnetic field distribution with the phantom scanning two-dimensionally above the oven. The signal source location was estimated by least squares fitting to the measured distribution. The goodness of fit value between the measured and the theoretical distributions was 97.9%.

On the feasibility of neurocurrent imaging by low-field nuclear magnetic resonance

We describe a nuclear magnetic resonance (NMR) spectrometer operating at 20 μT with a frequency resolution of 2 mHz to determine the intrinsic linewidth of the proton resonance in the human brain to be about 3 Hz. Using the same system we measured a biomagnetic field of 0.5 to 1 pT amplitude, which was generated by sustained brain activity evoked during repetitive median nerve stimulation. From these data, the effect of neuronal currents on the proton NMR signal was estimated. We conclude that neuronal currents may cause a measurable shift of the proton NMR line of brain tissue in low-fields.

Mapping the cardiomagnetic field with 19 room temperature second-order gradiometers

Event Abstract Back to Event Mapping the cardiomagnetic field with 19 room temperature second-order gradiometers Antoine Weis1*, Georg Bison2, Natascia Castagna1, Adrian Hofer1, Paul Knowles1, Jean-Luc Schenker1 and Malgorzata Kasprzak1 1 University of Fribourg, Switzerland 2 Friedrich-Schiller-University, Biomagnetic Center, Germany Objective: Optically pumped atomic magnetometers (LOPM) have become competitive with the well-established SQUID technology for recording biomagnetic fields. Since our first demonstration in 2003 [1] that a single gradiometer of two laser optically-pumped atomic magnetometers (LOPM) can be used for MCG mapping, we have struggled to develop multisensor arrays for recording field maps in clinically adapted measurement times. Methods: The field sensing element is a room-temperature Cs vapor contained in paraffin-coated cells [2]. The LOPM combines optical pumping by resonant laser light, rf-driven magnetic resonance, and laser readout to measure the magnetic field via spin precession. Digital phase detectors are used to either lock the field to the rf drive, or vice-versa. Coils permit feedback stabilization of the field in each sensor. With a set of feedback loops we have made 19 second order gradiometers (19+3+3 sensors in three planes) operated in an Al shielding room. RESULTS: The system has been successfully used [3] for recording heart field maps of more than 20 healthy subjects. Measurements on cardiac patients are in preparation and results shall be presented. Conclusion: We have demonstrated that a multisensor arrangement of laser pumped atomic magnetometers can be used for the simultaneous recording of cardiomagnetic field maps at 19 grid points in less than 2 minutes.