Quantum enabled functional neuroimaging: the why and how of magnetoencephalography using optically pumped magnetometers

Schofield, Holly; Boto, Elena; Shah, Vishal; Hill, Ryan M.; Osborne, James; Rea, Molly; Doyle, Cody; Holmes, Niall; Bowtell, Richard; Woolger, David; Brookes, Matthew J.

doi:10.1080/00107514.2023.2182950

Cited by 13 publications

(11 citation statements)

References 68 publications

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“…In recent years, MEG instrumentation has been revolutionised by the introduction of optically pumped magnetometers (OPMs). (See (Brookes et al, 2022;Schofield et al, 2023;Tierney et al, 2019) for reviews. )…”

Section: Introductionmentioning

confidence: 99%

“…This problem is notionally solved by operating sensors in a "closed-loop", mode, whereby sensors use negative feedback such that any changes in local field at the sensor are compensated by on-boardsensor electromagnetic coils. However, closed-loop operation is complicated since magnetic fields oriented in all three directions relative to the sensor affect the linearity of the response (Schofield et al, 2023;, meaning closed-loop operation is required on three independent axes. These limitations mean that OPM-MEG systems are not yet the "final product" and there remains significant scope for development.…”

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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Schofield,

Hill,

Feys

et al. 2024

Preprint

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“…[7,8], OPM-based MEG systems do not require expensive and bulky cooling equipment. These make them more costeffective and compact, thus expanding the application range of MEG [9,10]. In addition, the OPMs do not require cryogenics for cooling and can be placed closer to the scalp, facilitating the capture of finer spatial features [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Dynamic stabilisation of magnetic fields measured inside a magnetically shielded room using an external coil system ^*

Zhao,

Tian,

Sun

et al. 2024

J. Phys. D: Appl. Phys.

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Magnetoencephalography (MEG) system based on optically pumped magnetometers (OPMs) requires a magnetically shielded room (MSR) to establish a stable near-zero field environment. Affected by external environmental electromagnetic interference, the magnetic noise in the MSR will become very severe. In order to overcome this problem, this paper proposes a method for dynamic stabilisation of magnetic fields measured inside a MSR using an external coil system. Firstly, the field form of the external compensation coil was analyzed by taking the AC characteristics of the material into consideration. Then, the linear characteristic of the control system is studied and a high performance magnetic noise suppression controller is designed based on the environment noise characteristics. Finally, simulation and experimental are carried out through a self-developed 1250mm×1250mm×2100mm MSR, which indicates that the proposed method can effectively suppress dynamic magnetic fluctuation and noise.

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“…Since the 1960’s, MEG sensors have used superconducting quantum interference device (SQUID) technology, developing from single sensor recordings to commercially available whole-head high-density sensor arrays. Recent advances in the miniaturization of quantum sensors have seen the increased use of optically pumped magnetometer (OPM) technology for MEG recordings [5,6]. Studies of OPM MEG recordings indicate equivalent performance, as compared to SQUID MEG [7,8].…”

Section: Introductionmentioning

confidence: 99%

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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Quantum enabled functional neuroimaging: the why and how of magnetoencephalography using optically pumped magnetometers

Cited by 13 publications

References 68 publications

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

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

Dynamic stabilisation of magnetic fields measured inside a magnetically shielded room using an external coil system ^*

Noise Reduction and Localization Accuracy in a Mobile Magnetoencephalography System

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Quantum enabled functional neuroimaging: the why and how of magnetoencephalography using optically pumped magnetometers

Cited by 13 publications

References 68 publications

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

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

Dynamic stabilisation of magnetic fields measured inside a magnetically shielded room using an external coil system *

Noise Reduction and Localization Accuracy in a Mobile Magnetoencephalography System

Contact Info

Product

Resources

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Dynamic stabilisation of magnetic fields measured inside a magnetically shielded room using an external coil system ^*