Helium-4 magnetometers for room-temperature biomedical imaging: toward collective operation and photon-noise limited sensitivity

Fourcault, William; Romain, Rudy; Gal, G. Le; Bertrand, F.; Josselin, V.; Prado, Matthieu Le; Labyt, Étienne; Palacios-Laloy, Agustin

doi:10.1364/oe.420031

Cited by 40 publications

(34 citation statements)

References 32 publications

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“… Holmes et al., 2018 , 2019 ). Alternatively, OPMs could be adapted to operate in a ‘closed-loop’ mode, where the remnant magnetic fields are continuously modelled (for example, using a spherical harmonic field model (as in Mellor et al., 2021 ) and cancelled ( Fourcault et al., 2021 ; Nardelli et al., 2020 ).…”

Section: Discussionmentioning

confidence: 99%

Using OPMs to measure neural activity in standing, mobile participants

et al. 2021

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Optically pumped magnetometer-based magnetoencephalography (OP-MEG) can be used to measure neuromagnetic fields while participants move in a magnetically shielded room. Head movements in previous OP-MEG studies have been up to 20 cm translation and ∼30° rotation in a sitting position. While this represents a step-change over stationary MEG systems, naturalistic head movement is likely to exceed these limits, particularly when participants are standing up. In this proof-of-concept study, we sought to push the movement limits of OP-MEG even further. Using a 90 channel (45-sensor) whole-head OP-MEG system and concurrent motion capture, we recorded auditory evoked fields while participants were: (i) sitting still, (ii) standing up and still, and (iii) standing up and making large natural head movements continuously throughout the recording – maximum translation 120 cm, maximum rotation 198°. Following pre-processing, movement artefacts were substantially reduced but not eliminated. However, upon utilisation of a beamformer, the M100 event-related field localised to primary auditory regions. Furthermore, the event-related fields from auditory cortex were remarkably consistent across the three conditions. These results suggest that a wide range of movement is possible with current OP-MEG systems. This in turn underscores the exciting potential of OP-MEG for recording neural activity during naturalistic paradigms that involve movement (e.g. navigation), and for scanning populations who are difficult to study with stationary MEG (e.g. young children).

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Section: Discussionmentioning

confidence: 99%

Using OPMs to measure neural activity in standing, mobile participants

et al. 2021

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“…The architecture of the sensor detailed here directly derives from the ones developed in our laboratory for MEG applications whose detailed description can be found in [21], and the typical noise obtained with this technology is around 50 fT/√Hz for the X and Y axes, and 200 fT/√Hz for the third axis Z.…”

Section: Designmentioning

confidence: 99%

“…The required dynamic range of ±70 µT is by far much larger than the FWHM of the parametric resonances, so that a closed-loop mode operation of the sensor is mandatory [21]. This mode also provides better linearity characteristics to the OPM instrument, where open-loop cross-axis effects are also avoided.…”

Section: B Design Of the Electronicsmentioning

confidence: 99%

“…Most of these sensors rely on alkali operating in the SERF regime and have dynamic ranges of a few nT. Even if compensation of the magnetic field can improve this figure [18,21,22] the dynamic range is far from reaching the Earth field. Thus MCG and MEG recordings out of shieldings have been performed with scalar magnetometers [23,24], but scalar data is poorer than vector data [25,26].…”

Section: Introductionmentioning

confidence: 99%

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A 4He vector zero-field optically pumped magnetometer operated in the Earth-field

Bertrand

Boness

Fourcault

et al. 2021

Review of Scientific Instruments

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Low intrinsic noise, high bandwidth and high accuracy vector magnetometers are key components for many ground or space geophysical applications. Here we report the design and the test of a 4 He vector optically pumped magnetometer specifically dedicated to these needs. It is based on a parametric resonance magnetometer architecture operated in the Earth magnetic field with closed-loop compensation of the 3 components of the magnetic field. It provides offset-free vector measurements in a ±70 µT range with a DC to 1 kHz bandwidth. We demonstrate a vector sensitivity up to 130 fT/√Hz, which is about ten times better than the best available fluxgate magnetometers currently available for the same targeted applications.

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“…1). It is partially for this reason that alpha (8)(9)(10)(11)(12)(13)(14)(15), beta (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) and gamma (>30 Hz) activity has successfully been recorded with OP-MEG during movement [9], [10], [15], theta (4-8 Hz) has been recorded while the participant was unconstrained [16], but delta and infra-slow waves (<4 Hz) remain a topic of future research. A number of methods have been suggested for minimizing changes in the background magnetic field during an OP-MEG experiment, with the most successful involving the placement of electromagnetic coils around the participant [13], [17]- [19].…”

Section: Introductionmentioning

confidence: 99%

Magnetic Field Mapping and Correction for Moving OP-MEG

Mellor

Tierney

O'Neill

et al. 2022

IEEE Trans. Biomed. Eng.

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Background: Optically pumped magnetometers (OPMs) have made moving, wearable magnetoencephalography (MEG) possible. The OPMs typically used for MEG require a low background magnetic field to operate, which is achieved using both passive and active magnetic shielding. However, the background magnetic field is never truly zero Tesla, and so the field at each of the OPMs changes as the participant moves. This leads to position and orientation dependent changes in the measurements, which manifest as low frequency artefacts in MEG data. Objective: We modelled the spatial variation in the magnetic field and used the model to predict the movement artefact found in a dataset. Methods: We demonstrate a method for modelling this field with a triaxial magnetometer, then showed that we can use the same technique to predict the movement artefact in a real OPM-based MEG (OP-MEG) dataset. Results: Using an 86channel OP-MEG system, we found that this modelling method maximally reduced the power spectral density of the data by 27.8 ± 0.6 dB at 0 Hz, when applied over 5 s non-overlapping windows. Conclusion:The magnetic field inside our state-of-the art magnetically shielded room can be well described by low-order spherical harmonic functions. We achieved a large reduction in movement noise when we applied this model to OP-MEG data. Significance: Real-time implementation of this method could reduce passive shielding requirements for OP-MEG recording and allow the measurement of low-frequency brain activity during natural participant movement.

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Helium-4 magnetometers for room-temperature biomedical imaging: toward collective operation and photon-noise limited sensitivity

Cited by 40 publications

References 32 publications

Using OPMs to measure neural activity in standing, mobile participants

Using OPMs to measure neural activity in standing, mobile participants

A 4He vector zero-field optically pumped magnetometer operated in the Earth-field

Magnetic Field Mapping and Correction for Moving OP-MEG

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