Magnetoencephalography (MEG) measures human brain function via assessment of the magnetic fields generated by electrical activity in neurons. Despite providing high-quality spatiotemporal maps of ...electrophysiological activity, current MEG instrumentation is limited by cumbersome field sensing technologies, resulting in major barriers to utility. Here, we review a new generation of MEG technology that is beginning to lift many of these barriers. By exploiting quantum sensors, known as optically pumped magnetometers (OPMs), ‘OPM-MEG’ has the potential to dramatically outperform the current state of the art, promising enhanced data quality (better sensitivity and spatial resolution), adaptability to any head size/shape (from babies to adults), motion robustness (participants can move freely during scanning), and a less complex imaging platform (without reliance on cryogenics). We discuss the current state of this emerging technique and describe its far-reaching implications for neuroscience.
Magnetoencephalography (MEG) allows noninvasive electrophysiological imaging of human brain activity. However, current MEG technology has significant limitations.Optically pumped magnetometers (OPM)-MEG is a new type of MEG instrumentation, promising several advantages compared with conventional scanners: higher signal sensitivity, better spatial resolution, more uniform coverage, lifespan compliance, free movement of participants during scanning, and lower system complexity.We describe the principles underlying OPM-MEG and its components, including noncryogenic field sensors and magnetic shielding technologies.We discuss how the OPM-MEG technology is impacting neuroscience, enabling researchers to overcome limitations of conventional human imaging techniques and tackle new types of research questions.
Recently, optically pumped magnetometers (OPMs) using hybrid cells, which enclose two types of alkaline atoms, have been developed to homogenize sensor properties inside a hybrid cell. To measure ...very weak biomagnetic fields using the OPMs, it is necessary to suppress environmental magnetic noise. One of the effective ways to reduce the noise is differential measurements at more than two sensing locations. However, the frequency characteristics of hybrid OPMs are not well known, although those must be corrected to be unified. In this study, we carried out numerical simulation to correct the deviation of the resonance frequency for gradiometer configuration of a K-Rb hybrid OPM. We assumed that the static magnetic field was inhomogeneous, and considered the transfer function correcting the deviation of the frequency characteristics between two sensors. The results indicated that the correction improves the sensitivity of the differential output of the gradiometer due to noise reduction.
Double-beam atomic magnetometer (AM) working in spin-exchange relaxation-free (SERF) regime is drawing growing attention due to high sensitivity (femtotesla-level) and non-intrusion characteristics. ...Nowadays, chip integration of AMs in pursuit of dramatical reduction in volume has become a major trend as it is especially favorable for future high-spatial-resolution biomagnetism imaging. While micro-fabricated vapor cell with only two transparent windows (due to planar nano fabrication processes) has become the major obstacle to achieve double-beam scheme on chip. In this study, an ultra-compact on-chip double-beam scheme based on emerging metasurface is proposed for SERF atomic magnetometer application. With in-surface incident both pump light and probe light, this planar device enables optical-path manipulation of linearly-polarized probe beam to precise intersect with pump beam. Our method supports angle manipulation of probe light up to 45 degrees with efficiencies reaching 70%. The device is designed with silicon nitride with thickness of 0.6 um, which can be directly fabricated on the transparent window of vapor cell through basic CMOS compatible processes. In addition, there are more advantages of this method including dramatic volume reduction and potential low-cost mass fabrication, which is promising for future applications including high-resolution biomagnetism imaging and portable atomic devices.
•An ultra-compact on-chip double-beam scheme for atomic magnetometer application.•Metasurface enables optical-path manipulation of linearly-polarized beam.•Non-vertical double-beam scheme in chip-scale cells.•Supports angle manipulation of probe light up to 27 degrees with high efficiencies.•This device is compatible with nanofabrication platforms.
Green infrastructure (GI) is already known to be a suitable way to enhance air quality in urban environments. Living wall systems (LWS) can be implemented in locations where other forms of GI, such ...as trees or hedges, are not suitable. However, much debate remains about the variables that influence their particulate matter (PM) accumulation efficiency. This study attempts to clarify which plant species are relatively the most efficient in capturing PM and which traits are decisive when it comes to the implementation of a LWS. We investigated 11 plant species commonly used on living walls, located close to train tracks and roads. PM accumulation on leaves was quantified by magnetic analysis (Saturation Isothermal Remanent Magnetization (SIRM)). Several leaf morphological variables that could potentially influence PM capture were assessed, as well as the Wall Leaf Area Index. A wide range in SIRM values (2.74-417 μA) was found between all species. Differences in SIRM could be attributed to one of the morphological parameters, namely SLA (specific leaf area). This suggest that by just assessing SLA, one can estimate the PM capture efficiency of a plant species, which is extremely interesting for urban greeners. Regarding temporal variation, some species accumulated PM over the growing season, while others actually decreased in PM levels. This decrease can be attributed to rapid leaf expansion and variations in meteorology. Correct assessment of leaf age is important here; we suggest individual labeling of leaves for further studies. Highest SIRM values were found close to ground level. This suggests that, when traffic is the main pollution source, it is most effective when LWS are applied at ground level. We conclude that LWS can act as local sinks for PM, provided that species are selected correctly and systems are applied according to the state of the art.
With the widespread use of static magnetic fields (SMFs) in medicine, it is imperative to explore the biological effects of SMFs and the mechanisms underlying their effects on biological systems. The ...presence of magnetic materials within cells and organisms could affect various biological metabolism and processes, including stress responses, proliferation, and structural alignment. SMFs were generally found to be safe at the organ and organism levels. However. human subjects exposed to strong SMFs have reported side effects. In this review, we combined the magnetic properties of biological samples to illustrate the mechanism of action of SMFs on biological systems from a biophysical point of view. We suggest that the mechanisms of action of SMFs on biological systems mainly include the induction of electric fields and currents, generation of magnetic effects, and influence of electron spins. An electrolyte flowing in a static magnetic field generates an induced current and an electric field. Magnetomechanical effects include orientation effects upon subjecting biological samples to SMFs and movement of biological samples in strong field gradients. SMFs are thought to affect biochemical reaction rates and yields by influencing electron spin. This paper helps people how can harness the favorable biological effects of SMFs.
Following the rapid progress in the development of optically pumped magnetometer (OPM) technology for the measurement of magnetic fields in the femtotesla range, a successful assembly of individual ...sensors into an array of nearly identical sensors is within reach. Here, 25 microfabricated OPMs with footprints of 1 cm(3) were assembled into a conformal array. The individual sensors were inserted into three flexible belt-shaped holders and connected to their respective light sources and electronics, which reside outside a magnetically shielded room, through long optical and electrical cables. With this setup the fetal magnetocardiogram of a pregnant woman was measured by placing two sensor belts over her abdomen and one belt over her chest. The fetal magnetocardiogram recorded over the abdomen is usually dominated by contributions from the maternal magnetocardiogram, since the maternal heart generates a much stronger signal than the fetal heart. Therefore, signal processing methods have to be applied to obtain the pure fetal magnetocardiogram: orthogonal projection and independent component analysis. The resulting spatial distributions of fetal cardiac activity are in good agreement with each other. In a further exemplary step, the fetal heart rate was extracted from the fetal magnetocardiogram. Its variability suggests fetal activity. We conclude that microfabricated optically pumped magnetometers operating at room temperature are capable of complementing or in the future even replacing superconducting sensors for fetal magnetocardiography measurements.
In this paper we present a novel noninvasive approach to estimate current densities in the heart from magnetocardiography. The proposed algorithm uses nested optimization to model current densities ...in equally-sized voxels of myocardial tissue. First-order Thiran all-pass filters are used to describe the propagation between voxels.We demonstrate feasibility of the algorithm for a noise-free single-layer simulation. However, challenges remain, such as addressing measurement noise and optimizing propagation velocity. Overall, this approach has the potential to complement or replace invasive catheter-based electrophysiological studies for localization of arrhythmogenic tissue.
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