scholarly journals Improved spatio-temporal measurements of visually evoked fields using optically-pumped magnetometers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Aikaterini Gialopsou ◽  
Christopher Abel ◽  
T. M. James ◽  
Thomas Coussens ◽  
Mark G. Bason ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Quantum Interference ◽  
Time Lag ◽  
Operating Conditions ◽  
Pattern Reversal ◽  
Optically Pumped ◽  
Signal Tracking ◽  
Brain Responses ◽  
Recent Developments ◽  
Spatio Temporal

AbstractRecent developments in performance and practicality of optically-pumped magnetometers (OPMs) have enabled new capabilities in non-invasive brain function mapping through magnetoencephalography. In particular, the lack of cryogenic operating conditions allows for more flexible placement of sensor heads closer to the brain, leading to improved spatial resolution and source localisation capabilities. Through recording visually evoked brain fields (VEFs), we demonstrate that the closer sensor proximity can be exploited to improve temporal resolution. We use OPMs, and superconducting quantum interference devices (SQUIDs) for reference, to measure brain responses to flash and pattern reversal stimuli. We find highly reproducible signals with consistency across multiple participants, stimulus paradigms and sensor modalities. The temporal resolution advantage of OPMs is manifest in a twofold improvement, compared to SQUIDs. The capability for improved spatio-temporal signal tracing is illustrated by simultaneous vector recordings of VEFs in the primary and associative visual cortex, where a time lag on the order of 10–20 ms is consistently found. This paves the way for further spatio-temporal studies of neurophysiological signal tracking in visual stimulus processing, and other brain responses, with potentially far-reaching consequences for time-critical mapping of functionality in healthy and pathological brains.

scholarly journals Improved spatio-temporal measurements of visually evoked fields using optically-pumped magnetometers

2021 ◽  
Author(s):  
Aikaterini Gialopsou ◽  
Christopher Abel ◽  
Timothy M. James ◽  
Thomas Coussens ◽  
Mark G. Bason ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Quantum Interference ◽  
Time Lag ◽  
Peak Height ◽  
Operating Conditions ◽  
Pattern Reversal ◽  
Optically Pumped ◽  
Brain Surface ◽  
Brain Responses ◽  
Spatio Temporal

Recent developments in performance and practicality of optically pumped magnetometers have enabled new capabilities in non-invasive brain function mapping through magnetoencephalography (MEG). In particular the lack of need of cryogenic operating conditions allows for more flexible placement of the sensor heads closer to the brain surface, leading to improved spatial measurement resolution and increased source localisation capabilities. Through recordings of visually evoked brain fields (VEF) we demonstrate that the greater sensor proximity can be further exploited to improve the temporal resolution. We use an OPM and for reference a superconducting quantum interference device (SQUID) setup to measure brain responses to standard flash and pattern reversal stimuli. We find highly reproducible signals with consistency across multiple healthy participants, stimulus paradigms and sensor modalities. The temporal resolution advantage of OPMs is manifest in a fourfold enhanced ratio of magnetic signal peak height to temporal width as compared to SQUIDs. The resulting capability of improved spatio-temporal signal tracing is illustrated by simultaneous vector recordings of VEFs in the V1 and V2 areas of the visual cortex, where a time lag on the order of 10-20 ms is consistently found. This paves the way for further studies of spatio-temporal neurophysiological signal tracking in visual stimulus processing and other brain responses with potentially far-reaching consequences for time-critical mapping of functionality in the healthy and pathological brain.

scholarly journals Detection of the 40-Hz Auditory Steady-state Response with Optically Pumped Magnetometers

2021 ◽  
Author(s):  
Kyung-min An ◽  
Jung Hyun Shim ◽  
Hyukchan Kwon ◽  
Young-Ho Lee ◽  
Kwon-Kyu Yu ◽  
...  
Keyword(s):  
Steady State ◽  
Quantum Interference ◽  
Functional Neuroimaging ◽  
Cryogenic Cooling ◽  
Optically Pumped ◽  
Temporal Area ◽  
Brain Responses ◽  
Steady State Responses ◽  
Auditory Steady State Responses ◽  
40 Hz

Magnetoencephalography (MEG) is a functional neuroimaging technique that noninvasively detects the brain magnetic field from neuronal activations. Conventional MEG measures brain signals using superconducting quantum interference devices (SQUIDs). SQUID based MEG requires a cryogenic environment involving a bulky non-magnetic dewar and the consumption of liquid helium, which restricts the variability of the sensor array and the gap between the cortical sources and sensors. Recently, miniature optically pumped magnetometers (OPMs) have been developed and commercialized. OPMs do not require cryogenic cooling and can be placed within millimeters from the scalp. In the present study, we arranged six OPM sensors on the temporal area to detect auditory related brain responses in a two layer magnetically shielded room. We presented the auditory stimuli of 1 kHz pure tone bursts with 200 ms duration and obtained the M50 and M100 components of auditory evoked fields. We delivered the periodic stimuli with a 40 Hz repetition rate and observed the gamma band power changes and inter trial phase coherence of auditory steady state responses at 40 Hz. We found that the OPM sensors have a performance comparable to that of conventional SQUID based MEG sensors, and our results suggest the feasibility of using OPM sensors for functional neuroimaging and brain computer interface applications.

scholarly journals A data reduction and compression description for high throughput time-resolved electron microscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Abhik Datta ◽  
Kian Fong Ng ◽  
Deepan Balakrishnan ◽  
Melissa Ding ◽  
See Wee Chee ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Temporal Resolution ◽  
Data Reduction ◽  
Accurate Estimation ◽  
Data Streaming ◽  
Compression Scheme ◽  
Raw Data ◽  
Time Resolved ◽  
Detection And Counting ◽  
Spatio Temporal

AbstractFast, direct electron detectors have significantly improved the spatio-temporal resolution of electron microscopy movies. Preserving both spatial and temporal resolution in extended observations, however, requires storing prohibitively large amounts of data. Here, we describe an efficient and flexible data reduction and compression scheme (ReCoDe) that retains both spatial and temporal resolution by preserving individual electron events. Running ReCoDe on a workstation we demonstrate on-the-fly reduction and compression of raw data streaming off a detector at 3 GB/s, for hours of uninterrupted data collection. The output was 100-fold smaller than the raw data and saved directly onto network-attached storage drives over a 10 GbE connection. We discuss calibration techniques that support electron detection and counting (e.g., estimate electron backscattering rates, false positive rates, and data compressibility), and novel data analysis methods enabled by ReCoDe (e.g., recalibration of data post acquisition, and accurate estimation of coincidence loss).

scholarly journals Towards the Hydrogen Economy—A Review of the Parameters That Influence the Efficiency of Alkaline Water Electrolyzers

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3193
Author(s):  
Ana L. Santos ◽  
Maria-João Cebola ◽  
Diogo M. F. Santos
Keyword(s):  
Energy Content ◽  
Water Electrolysis ◽  
High Energy ◽  
Operating Conditions ◽  
Energy Sources ◽  
Alkaline Water Electrolysis ◽  
Alkaline Water ◽  
New Energy ◽  
Recent Developments ◽  
Cell Components

Environmental issues make the quest for better and cleaner energy sources a priority. Worldwide, researchers and companies are continuously working on this matter, taking one of two approaches: either finding new energy sources or improving the efficiency of existing ones. Hydrogen is a well-known energy carrier due to its high energy content, but a somewhat elusive one for being a gas with low molecular weight. This review examines the current electrolysis processes for obtaining hydrogen, with an emphasis on alkaline water electrolysis. This process is far from being new, but research shows that there is still plenty of room for improvement. The efficiency of an electrolyzer mainly relates to the overpotential and resistances in the cell. This work shows that the path to better electrolyzer efficiency is through the optimization of the cell components and operating conditions. Following a brief introduction to the thermodynamics and kinetics of water electrolysis, the most recent developments on several parameters (e.g., electrocatalysts, electrolyte composition, separator, interelectrode distance) are highlighted.

Optically pumped magnetometers enable a new level of biomagnetic measurements

2020 ◽  
Vol 9 (5) ◽  
pp. 247-251
Author(s):  
Tilmann Sander ◽  
Anna Jodko-Władzińska ◽  
Stefan Hartwig ◽  
Rüdiger Brühl ◽  
Thomas Middelmann
Keyword(s):  
Quantum Interference ◽  
High Sensitivity ◽  
High Temporal Resolution ◽  
Optically Pumped ◽  
New Class ◽  
Magnetic Shields ◽  
Highly Sensitive ◽  
Electric And Magnetic Fields ◽  
Auditory Evoked Fields

AbstractThe electrophysiological activities in the human body generate electric and magnetic fields that can be measured noninvasively by electrodes on the skin, or even, not requiring any contact, by magnetometers. This includes the measurement of electrical activity of brain, heart, muscles and nerves that can be measured in vivo and allows to analyze functional processes with high temporal resolution. To measure these extremely small magnetic biosignals, traditionally highly sensitive superconducting quantum-interference devices have been used, together with advanced magnetic shields. Recently, they have been complemented in usability by a new class of sensors, optically pumped magnetometers (OPMs). These quantum sensors offer a high sensitivity without requiring cryogenic temperatures, allowing the design of small and flexible sensors for clinical applications. In this letter, we describe the advantages of these upcoming OPMs in two exemplary applications that were recently carried out at Physikalisch-Technische Bundesanstalt (PTB): (1) magnetocardiography (MCG) recorded during exercise and (2) auditory-evoked fields registered by magnetoencephalography.

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