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Movement correction and clinical implementation of wearable magnetoencephalography (MEG)

Mellor, Stephanie; (2023) Movement correction and clinical implementation of wearable magnetoencephalography (MEG). Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Magnetoencephalography (MEG) is the non-invasive measurement of magnetic fields due to neuronal current flow. The magnitude of the magnetic fields (10 fT to 1000 fT) is millions of times smaller than the Earth’s static field. Consequently, highly sensitive magnetic sensors are required for MEG. Until recently, MEG systems have been based on sensors requiring cryogenic cooling. Hardware limitations from this cooling have made MEG systems large, immobile and expensive. In recent years, Optically Pumped Magnetometers (OPMs) have become viable sensors with which to measure neuromagnetic fields. These can be placed directly on the scalp. This wearability means that the participant is no longer required to remain still and the cost of the system, both financial and in terms of space, is generally lower. The freedom of movement opens up new neuroscientific and clinical applications. However, this new system is not without limitations. Movement in particular leads to artefacts unlike those previously seen in MEG; the OPM properties (gain, sensitive axis orientation, phase) are dependent on the ambient magnetic field at the sensor, which changes with position. In this thesis, we look at the impact of movement on OPM based MEG (OP-MEG) and how it can be reduced. In Chapter 2, we look into the cause of movement artefacts in OP-MEG, by mapping the spatial variation in the background magnetic field in our OP-MEG system. We show that the field varies both spatially and temporally, and that by modelling it we can reduce the interference in an OP-MEG recording. In Chapters 3 and 4, we correct for this changing field in real-time, first in simulation and then empirically. Based on the simulation results, we updated our empirical method to remove reliance on recording the position of the participant and to minimise time delays in providing the correction. Finally, in Chapters 5 and 6, we record interictal (between seizure) and ictal (seizure) OP-MEG in patients with epilepsy, while considering the impact movement has on the recordings and interictal event detection.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Movement correction and clinical implementation of wearable magnetoencephalography (MEG)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Imaging Neuroscience
URI: https://discovery.ucl.ac.uk/id/eprint/10168534
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