Enabling ambulatory movement in wearable magnetoencephalography with matrix coil active magnetic shielding

Holmes, Niall; Rea, Molly; Hill, Ryan M.; Leggett, James; Edwards, Lucy J; Hobson, P. J.; Boto, Elena; Tierney, Tim M.; Rier, Lukas; Rivero, G.; Shah, Vishal; Osborne, James; Fromhold, T. M.; Glover, Paul; Brookes, Matthew J.; Bowtell, Richard

doi:10.1016/j.neuroimage.2023.120157

Cited by 33 publications

(24 citation statements)

References 63 publications

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“…A similar dry phantom design resulted in 1-2mm localization error when used in a whole head SQUID MEG system, although this accuracy was achieved after re-calibration of the phantom [20]. In OPM MEG, similar or better localization accuracy has been reported for a dry phantom, however dipole magnitudes in this case were on the order of 1 uAm, which is two orders of magnitude larger than brain activity [14,33]. Phantom localization error of 5 mm was found for a 1-cm current source inside of a saline solution sphere using OPM MEG sensors [10].…”

Section: Discussionmentioning

confidence: 62%

Noise Reduction and Localization Accuracy in a Mobile Magnetoencephalography System

Bardouille,

Smith,

Vajda

et al. 2024

Preprint

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Magnetoencephalography (MEG) non-invasively provides important information about human brain electrophysiology. The growing use of optically pumped magnetometers (OPM) for MEG, as opposed to fixed arrays of cryogenic sensors, has opened the door for innovation in system design and use cases. For example, cryogenic MEG systems are housed in large shielded rooms to provide sufficient space for the system dewar. Here, we investigate the performance of OPM recordings inside of a cylindrical shield with a 1×2 m2footprint. The efficacy of shielding was measured in terms of field attenuation and isotropy, and the value of post hoc noise reduction algorithms was also investigated. Localization accuracy was quantified for 104 OPM sensors mounted on a fixed helmet array based on simulations and recordings from a bespoke current dipole phantom. Passive shielding attenuated direct current (DC) and power line (60 Hz) fields by approximately 60 dB, and all other frequencies by 80-90 dB. Post hoc noise reduction provided an additional 5-15 dB attenuation. Substantial field anisotropy remained in the volume encompassing the sensor array. The consistency of the anisotropy over months suggests that a field nulling solution could be readily applied. A current dipole phantom generating source activity at an appropriate magnitude for the human brain generated field fluctuations on the order of 0.5-1 pT. Phantom signals were localized with 3 mm localization accuracy and no significant bias in localization was observed, which is in line with performance for cryogenic and OPM MEG systems. This validation of the performance of a small footprint MEG system opens the door for lower cost MEG installations in terms of raw materials and facility space, as well as mobile imaging systems (e.g., truck-based). Such implementations are relevant for global adoption of MEG outside of highly resourced research and clinical institutions.

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Section: Discussionmentioning

confidence: 62%

Noise Reduction and Localization Accuracy in a Mobile Magnetoencephalography System

Bardouille,

Smith,

Vajda

et al. 2024

Preprint

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“…Secondly, closed-loop operation means that sensor output remains linear even when the sensors move through a large background field; this enables sensors to keep working when the subject moves (as demonstrated in Figure 4). In previous demonstrations of free movement (Holmes et al, 2018(Holmes et al, , 2023Rea et al, 2022), sensor linearity has been enabled by the use of large coils -either mounted on planes each side of the subject, or within the MSR walls -which create a zero field volume enclosing the head. In principle, closed-loop operation offers an alternative to use of such coils.…”

Section: Discussionmentioning

confidence: 99%

“…Adaptability also means arrays can be designed to optimise sensitivity to specific effects (Hill et al, 2024) or brain areas (Lin et al, 2019; Tierney, Levy, et al, 2021). As the sensors move with the head, participants can move freely during recordings (assuming background fields are well controlled) (Holmes et al, 2018, 2019, 2023; Rea et al, 2021). This enables the recording of data during novel tasks (Boto et al, 2018; Rea et al, 2022) or even epileptic seizures (Feys, et al, 2023; Hillebrand et al, 2023).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, when systems have large sensor counts, cabling becomes cumbersome with large numbers of wires trailing from the subject. While this is fine for static systems, for systems where the aim is to allow the subject to move freely (even to walk around a room (Holmes et al, 2023)), having heavy cabling draped around a participant is impractical – particularly in the case of patients.…”

Section: Introductionmentioning

confidence: 99%

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A Novel, Robust, and Portable Platform for Magnetoencephalography using Optically Pumped Magnetometers

Schofield,

Hill,

Feys

et al. 2024

Preprint

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Magnetoencephalography (MEG) measures brain function via assessment of magnetic fields generated by neural currents. Conventional MEG uses superconducting sensors, which place significant limitations on performance, practicality, and deployment; however, the field has been revolutionised in recent years by the introduction of optically-pumped-magnetometers (OPMs). OPMs enable measurement of the MEG signal without cryogenics, and consequently the conception of ‘OPM-MEG’ systems which ostensibly allow increased sensitivity and resolution, lifespan compliance, free subject movement, and lower cost. However, OPM-MEG remains in its infancy with limitations on both sensor and system design. Here, we report a new OPM-MEG design with miniaturised and integrated electronic control, a high level of portability, and improved sensor dynamic range (arguably the biggest limitation of existing instrumentation). We show that this system produces equivalent measures when compared to an established instrument; specifically, when measuring task-induced beta-band, gamma-band and evoked neuro-electrical responses, source localisations from the two systems were highly comparable and temporal correlation was >0.7 at the individual level and >0.9 for groups. Using an electromagnetic phantom, we demonstrate improved dynamic range by running the system in background fields up to 8 nT. We show that the system is effective in gathering data during free movement (including a sitting-to-standing paradigm) and that it is compatible with simultaneous electroencephalography (EEG – the clinical standard). Finally, we demonstrate portability by moving the system between two laboratories. Overall, our new system is shown to be a significant step forward for OPM-MEG technology and offers an attractive platform for next generation functional medical imaging.

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“…MEG normally requires the detection of both magnetic fields and magnetic field gradients, with the latter enabling higher spatial resolution and better localization of the biomagnetic source [25][26][27][28]. In general, the measurement of the small magnetic fields produced by the human body is strongly affected by environmental magnetic field noise, whose cancellation and shielding is expensive and cumbersome [21,[29][30][31]. Measuring magnetic field gradients can help in circumventing or simplifying this problem.…”

Section: Introductionmentioning

confidence: 99%

An optically pumped magnetic gradiometer for the detection of human biomagnetism

Cook,

Bezsudnova,

Koponen

et al. 2024

Quantum Sci. Technol.

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We realise an intrinsic optically pumped magnetic gradiometer based on non-linear magneto-optical rotation. We show that our sensor can reach a gradiometric sensitivity of 18 fT/cm/√Hz and can reject common mode homogeneous magnetic field noise with up to 30 dB attenuation. We demonstrate that our magnetic field gradiometer is sufficiently sensitive and resilient to be employed in biomagnetic applications. In particular, we are able to record the auditory evoked response of the human brain, and to perform real-time magnetocardiography in the presence of external magnetic field disturbances. Our gradiometer provides complementary capabilities in human biomagnetic sensing to optically pumped magnetometers, and opens new avenues in the detection of human biomagnetism.

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Enabling ambulatory movement in wearable magnetoencephalography with matrix coil active magnetic shielding

Cited by 33 publications

References 63 publications

Noise Reduction and Localization Accuracy in a Mobile Magnetoencephalography System

Noise Reduction and Localization Accuracy in a Mobile Magnetoencephalography System

A Novel, Robust, and Portable Platform for Magnetoencephalography using Optically Pumped Magnetometers

An optically pumped magnetic gradiometer for the detection of human biomagnetism

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