scholarly journals On-scalp MEG system utilizing an actively shielded array of optically-pumped magnetometers

2018 ◽  
Author(s):  
Joonas Iivanainen ◽  
Rasmus Zetter ◽  
Mikael Grön ◽  
Karoliina Hakkarainen ◽  
Lauri Parkkonen
Keyword(s):  
Spin Exchange ◽  
Dynamic Control ◽  
Sensor Arrays ◽  
Low Frequency ◽  
Sensor Calibration ◽  
Optically Pumped ◽  
Magnetic Shields ◽  
Brain Responses ◽  
Shielding Factor ◽  
Magnetically Shielded Room

AbstractThe spatial resolution of magnetoencephalography (MEG) can be increased from that of conventional SQUID-based systems by employing on-scalp sensor arrays of e.g. optically-pumped magnetometers (OPMs). However, OPMs reach sufficient sensitivity for neuromagnetic measurements only when operated in a very low absolute magnetic field of few nanoteslas or less, usually not reached in a typical magnetically shielded room constructed for SQUID-based MEG. Moreover, field drifts affect the calibration of OPMs. Static and dynamic control of the ambient field is thus necessary for good-quality neuromagnetic measurements with OPMs. Here, we describe an on-scalp MEG system that utilizes OPMs and external compensation coils that provide static and dynamic shielding against ambient fields.In a conventional two-layer magnetically shielded room, our coil system reduced the maximum remanent DC-field component within an 8-channel OPM array from 70 to less than 1 nT, enabling the sensors to operate in the sensitive spin exchange relaxation-free regime. When compensating field drifts below 4 Hz, a low-frequency shielding factor of 22 dB was achieved, which reduced the peak-to-peak drift from 1.3 to 0.4 nT and thereby the standard deviation of the sensor calibration from 1.6% to 0.4%. Without band-limiting the field that is compensated, a low-frequency shielding factor of 43 dB was achieved.We validated the system by measuring brain responses to electric stimulation of the median nerve. With dynamic shielding and digital interference suppression methods, single-trial somatosensory evoked responses could be detected. Our results advance the deployment of OPM-based on-scalp MEG in lighter magnetic shields.

scholarly journals Compensation System for Biomagnetic Measurements with Optically Pumped Magnetometers inside a Magnetically Shielded Room

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4563 ◽  
Author(s):  
Anna Jodko-Władzińska ◽  
Krzysztof Wildner ◽  
Tadeusz Pałko ◽  
Michał Władziński
Keyword(s):  
Magnetic Field ◽  
Quantum Interference ◽  
Spin Exchange ◽  
Initial Conditions ◽  
Sensor Arrays ◽  
Compensation System ◽  
Zero Field ◽  
Optically Pumped ◽  
Ambient Magnetic Field ◽  
Magnetically Shielded Room

Magnetography with superconducting quantum interference device (SQUID) sensor arrays is a well-established technique for measuring subtle magnetic fields generated by physiological phenomena in the human body. Unfortunately, the SQUID-based systems have some limitations related to the need to cool them down with liquid helium. The room-temperature alternatives for SQUIDs are optically pumped magnetometers (OPM) operating in spin exchange relaxation-free (SERF) regime, which require a very low ambient magnetic field. The most common two-layer magnetically shielded rooms (MSR) with residual magnetic field of 50 nT may not be sufficiently magnetically attenuated and additional compensation of external magnetic field is required. A cost-efficient compensation system based on square Helmholtz coils was designed and successfully used for preliminary measurements with commercially available zero-field OPM. The presented setup can reduce the static ambient magnetic field inside a magnetically shielded room, which improves the usability of OPMs by providing a proper environment for them to operate, independent of initial conditions in MSR.

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.

scholarly journals Depressive rumination is correlated with brain responses during self-related processing

2021 ◽  
Author(s):  
Tzu-Yu Hsu ◽  
Tzu-Ling Liu ◽  
Paul Z. Cheng ◽  
Hsin-Chien Lee ◽  
Timothy J. Lane ◽  
...  
Keyword(s):  
Depressive Symptoms ◽  
Low Frequency ◽  
Event Related Potentials ◽  
Unipolar Depression ◽  
Brain Responses ◽  
Late Event ◽  
Oscillatory Power ◽  
Related Aspect ◽  
Related Potentials ◽  
Central Symptom

AbstractBackgroundRumination, a tendency to focus on negative self-related thoughts, is a central symptom of depression. Studying the self-related aspect of such symptoms is challenging due to the need to distinguish self effects per se from the emotional content of task stimuli. This study employs an emotionally neutral self-related paradigm to investigate possible altered self processing in depression and its link to rumination.MethodsPeople with unipolar depression (MDD; n = 25) and controls (n = 25) underwent task-based EEG recording. Late event-related potentials were studied along with low frequency oscillatory power. EEG metrics were compared between groups and correlated with depressive symptoms and reported rumination.ResultsThe MDD group displayed a difference in late potentials across fronto-central electrodes between self-related and non-self-related conditions. No such difference was seen in controls. The magnitude of this difference was positively related with depressive symptoms and reported rumination. MDD also had elevated theta oscillation power at central electrodes in self-related conditions, which was not seen in controls.ConclusionsRumination appears linked to altered self-related processing in depression, independently of stimuli-related emotional confounds. This connection between self-related processing and depression may point to self-disorder being a core component of the condition.

scholarly journals Low frequency steady-state brain responses modulate large scale functional networks in a frequency-specific means

2015 ◽  
Vol 37 (1) ◽  
pp. 381-394 ◽  
Author(s):  
Yi-Feng Wang ◽  
Zhiliang Long ◽  
Qian Cui ◽  
Feng Liu ◽  
Xiu-Juan Jing ◽  
...  
Keyword(s):  
Steady State ◽  
Large Scale ◽  
Low Frequency ◽  
Functional Networks ◽  
Brain Responses

Enhancement of optically pumped spin orientation via spin-exchange collisions at low vapor density

2012 ◽  
Vol 85 (4) ◽  
Author(s):  
W. Chalupczak ◽  
R. M. Godun ◽  
P. Anielski ◽  
A. Wojciechowski ◽  
S. Pustelny ◽  
...  
Keyword(s):  
Spin Exchange ◽  
Vapor Density ◽  
Optically Pumped ◽  
Spin Orientation

Behavioral and Brain Responses Highlight the Role of Usage in the Preparation of Multiword Utterances for Production

2021 ◽  
pp. 1-34
Author(s):  
Hyein Jeong ◽  
Emiel van den Hoven ◽  
Sylvain Madec ◽  
Audrey Bürki
Keyword(s):  
Language Processing ◽  
Time Windows ◽  
Low Frequency ◽  
Balanced Design ◽  
Brain Responses ◽  
Functional Locus ◽  
Linguistic Representations ◽  
Electrophysiological Signal ◽  
The Brain ◽  
Naming Latencies

Abstract Usage-based theories assume that all aspects of language processing are shaped by the distributional properties of the language. The frequency not only of words but also of larger chunks plays a major role in language processing. These theories predict that the frequency of phrases influences the time needed to prepare these phrases for production and their acoustic duration. By contrast, dominant psycholinguistic models of utterance production predict no such effects. In these models, the system keeps track of the frequency of individual words but not of co-occurrences. This study investigates the extent to which the frequency of phrases impacts naming latencies and acoustic duration with a balanced design, where the same words are recombined to build high- and low-frequency phrases. The brain signal of participants is recorded so as to obtain information on the electrophysiological bases and functional locus of frequency effects. Forty-seven participants named pictures using high- and low-frequency adjective–noun phrases. Naming latencies were shorter for high-frequency than low-frequency phrases. There was no evidence that phrase frequency impacted acoustic duration. The electrophysiological signal differed between high- and low-frequency phrases in time windows that do not overlap with conceptualization or articulation processes. These findings suggest that phrase frequency influences the preparation of phrases for production, irrespective of the lexical properties of the constituents, and that this effect originates at least partly when speakers access and encode linguistic representations. Moreover, this study provides information on how the brain signal recorded during the preparation of utterances changes with the frequency of word combinations.

Polarization of3Heby Spin Exchange with Optically Pumped Rb and K Vapors

1998 ◽  
Vol 80 (13) ◽  
pp. 2801-2804 ◽  
Author(s):  
A. Ben-Amar Baranga ◽  
S. Appelt ◽  
M. V. Romalis ◽  
C. J. Erickson ◽  
A. R. Young ◽  
...  
Keyword(s):  
Spin Exchange ◽  
Optically Pumped

scholarly journals Technique for high axial shielding factor performance of large-scale, thin, open-ended, cylindrical Metglas magnetic shields

2011 ◽  
Vol 82 (7) ◽  
pp. 075104 ◽  
Author(s):  
S. Malkowski ◽  
R. Adhikari ◽  
B. Hona ◽  
C. Mattie ◽  
D. Woods ◽  
...  
Keyword(s):  
Large Scale ◽  
Magnetic Shields ◽  
Shielding Factor
Sign in / Sign up

Export Citation Format

Share Document