Requirements for coregistration accuracy in on-scalp MEG

Zetter, Rasmus; Iivanainen, Joonas; Stenroos, Matti; Parkkonen, Lauri

doi:10.1101/176545

Cited by 3 publications

(4 citation statements)

References 76 publications

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“…We have previously shown that the optical coregistration method we applied in the OPM measurement is sufficiently accurate for on‐scalp MEG (Zetter et al, , ). Thus, coregistration error should not be the limiting factor when improving OPM source estimates beyond those obtained from SQUID data.…”

Section: Discussionmentioning

confidence: 99%

“…With open‐loop OPMs—such as the ones used here—crosstalk mainly changes the gain of the sensor and the orientation of its sensitive axis (Tierney et al, ). If crosstalk is not taken into account, it will cause source‐estimation errors (Zetter et al, ). We do not believe that crosstalk will be a severe issue in dense open‐loop OPM arrays.…”

Section: Discussionmentioning

confidence: 99%

“…Forward models were computed using the MRI‐derived three‐shell boundary element models (see Section 2.2). OPMs were modeled as by Zetter, Iivanainen, Stenroos, and Parkkonen (), with eight integration points equally spaced within a 3‐mm cube corresponding to the sensitive volume of the sensor. SQUIDs were modeled as in the MNE software.…”

Section: Methodsmentioning

confidence: 99%

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Potential of on‐scalp MEG: Robust detection of human visual gamma‐band responses

Iivanainen

Zetter

Parkkonen

2019

Human Brain Mapping

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Electrophysiological signals recorded intracranially show rich frequency content spanning from near‐DC to hundreds of hertz. Noninvasive electromagnetic signals measured with electroencephalography (EEG) or magnetoencephalography (MEG) typically contain less signal power in high frequencies than invasive recordings. Particularly, noninvasive detection of gamma‐band activity (>30 Hz) is challenging since coherently active source areas are small at such frequencies and the available imaging methods have limited spatial resolution. Compared to EEG and conventional SQUID‐based MEG, on‐scalp MEG should provide substantially improved spatial resolution, making it an attractive method for detecting gamma‐band activity. Using an on‐scalp array comprised of eight optically pumped magnetometers (OPMs) and a conventional whole‐head SQUID array, we measured responses to a dynamic visual stimulus known to elicit strong gamma‐band responses. OPMs had substantially higher signal power than SQUIDs, and had a slightly larger relative gamma‐power increase over the baseline. With only eight OPMs, we could obtain gamma‐activity source estimates comparable to those of SQUIDs at the group level. Our results show the feasibility of OPMs to measure gamma‐band activity. To further facilitate the noninvasive detection of gamma‐band activity, the on‐scalp OPM arrays should be optimized with respect to sensor noise, the number of sensors and intersensor spacing.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Potential of on‐scalp MEG: Robust detection of human visual gamma‐band responses

Iivanainen

Zetter

Parkkonen

2019

Human Brain Mapping

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“…Optically pumped magnetometers (OPMs) have attracted increasing attention in neuroscientific research over the last few years (e.g., Alem et al, 2014;Boto et al, 2017Boto et al, , 2018Hill et al, 2019;Iivanainen et al, 2020;Roberts et al, 2019;Zetter et al, 2018). Without the need to be cooled to cryogenic temperatures like superconducting quantum interference device (SQUID) magnetometers, OPMs require relatively minimal insulation and do not need to be mounted at fixed locations within a dewar like traditional MEG.…”

Section: Introductionmentioning

confidence: 99%

Contactless recordings of retinal activity using optically pumped magnetometers

Westner

Lubell

Jensen

et al. 2021

Preprint

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Optically pumped magnetometers (OPMs) have been adopted for the recording of brain activity. Without the need to be cooled to cryogenic temperatures, an array of these sensors can be placed more flexibly, which allows for the recording of neuronal structures other than neocortex. Here we use eight OPM sensors to record human retinal activity following flash stimulation. We compare this magnetoretinographic (MRG) activity to the simultaneously recorded electroretinogram of the eight participants. The MRG shows the familiar flash-evoked potentials (a-wave and b-wave) and shares a highly significant amount of information with the electroretinogram recording (both in a simultaneous and separate recording). We conclude that OPM sensors have the potential to become a contactless alternative to fiber electrodes for the recording of retinal activity. Such a contactless solution can benefit both clinical and neuroscientific settings.

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

Iivanainen¹,

Zetter²,

Groen³

et al. 2018

Preprint

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The 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.

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Requirements for coregistration accuracy in on-scalp MEG

Cited by 3 publications

References 76 publications

Potential of on‐scalp MEG: Robust detection of human visual gamma‐band responses

Potential of on‐scalp MEG: Robust detection of human visual gamma‐band responses

Contactless recordings of retinal activity using optically pumped magnetometers

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

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