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2. Interference suppression techniques for OPM-based MEG: Opportunities and challenges

Author

Seymour, Robert A, Alexander, Nicholas, Mellor, Stephanie, O'Neill, George C, Tierney, Tim M, Barnes, Gareth R, and Maguire, Eleanor A

Subjects
Quantitative Biology - Neurons and Cognition, Quantitative Biology - Quantitative Methods
Abstract

One of the primary technical challenges facing magnetoencephalography (MEG) is that the magnitude of neuromagnetic fields is several orders of magnitude lower than interfering signals. Recently, a new type of sensor has been developed - the optically pumped magnetometer (OPM). These sensors can be placed directly on the scalp and move with the head during participant movement, making them wearable. This opens up a range of exciting experimental and clinical opportunities for OPM-based MEG experiments, including paediatric studies, and the incorporation of naturalistic movements into neuroimaging paradigms. However, OPMs face some unique challenges in terms of interference suppression, especially in situations involving mobile participants, and when OPMs are integrated with electrical equipment required for naturalistic paradigms, such as motion capture systems. Here we briefly review various hardware solutions for OPM interference suppression. We then outline several signal processing strategies aimed at increasing the signal from neuromagnetic sources. These include regression-based strategies, temporal filtering and spatial filtering approaches. The focus is on the practical application of these signal processing algorithms to OPM data. In a similar vein, we include two worked-through experiments using OPM data collected from a whole-head sensor array. These tutorial-style examples illustrate how the steps for suppressing external interference can be implemented, including the associated data and code so that researchers can try the pipelines for themselves. With the popularity of OPM-based MEG rising, there will be an increasing need to deal with interference suppression. We hope this practical paper provides a resource for OPM-based MEG researchers to build upon., Comment: 56 pages, 19 figures, supplementary materials available on request

Published
2021

8. A lightweight magnetically shielded room with active shielding

Author

Holmes, Niall, Rea, Molly, Chalmers, James, Leggett, James, Edwards, Lucy J., Nell, Paul, Pink, Stephen, Patel, Prashant, Wood, Jack, Murby, Nick, Woolger, David, Dawson, Eliot, Mariani, Christopher, Tierney, Tim M., Mellor, Stephanie, O’Neill, George C., Boto, Elena, Hill, Ryan M., Shah, Vishal, Osborne, James, Pardington, Rosemarie, Fierlinger, Peter, Barnes, Gareth R., Glover, Paul, Brookes, Matthew J., and Bowtell, Richard

Published
2022
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9. Towards non-invasive imaging through spinal-cord generated magnetic fields.

Author

Spedden, Meaghan E., O'Neill, George C., Tierney, Tim M., West, Timothy O., Schmidt, Maike, Mellor, Stephanie, Farmer, Simon F., Bestmann, Sven, and Barnes, Gareth R.

Subjects
SPINAL cord physiology, SPINAL cord diseases, OPTICS, ULTRASONIC encephalography, MAGNETIC resonance imaging, MAGNETICS, CRYOSURGERY, MINIMALLY invasive procedures, LARGE-scale brain networks, NEURORADIOLOGY, BIOMARKERS
Abstract

Non-invasive imaging of the human spinal cord is a vital tool for understanding the mechanisms underlying its functions in both healthy and pathological conditions. However, non-invasive imaging presents a significant methodological challenge because the spinal cord is difficult to access with conventional neurophysiological approaches, due to its proximity to other organs and muscles, as well as the physiological movements caused by respiration, heartbeats, and cerebrospinal fluid (CSF) flow. Here, we discuss the present state and future directions of spinal cord imaging, with a focus on the estimation of current flow through magnetic field measurements. We discuss existing cryogenic (superconducting) and non-cryogenic (optically-pumped magnetometer-based, OPM) systems, and highlight their strengths and limitations for studying human spinal cord function. While significant challenges remain, particularly in source imaging and interference rejection, magnetic field-based neuroimaging offers a novel avenue for advancing research in various areas. These include sensorimotor processing, cortico-spinal interplay, brain and spinal cord plasticity during learning and recovery from injury, and pain perception. Additionally, this technology holds promise for diagnosing and optimizing the treatment of spinal cord disorders. [ABSTRACT FROM AUTHOR]

Published
2024
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14. Is Bonferroni correction more sensitive than Random Field Theory for most fMRI studies?

Author

Tierney, Tim M., Clark, Christopher A., and Carmichael, David W.

Subjects
Statistics - Applications, Physics - Medical Physics
Abstract

Random Field Theory has been used in the fMRI literature to address the multiple comparisons problem. The method provides an analytical solution for the computation of precise p-values when its assumptions are met. When its assumptions are not met the thresholds generated by Random Field Theory can be more conservative than Bonferroni corrections, which are arguably too stringent for use in fMRI. As this has been well documented theoretically it is surprising that a majority of current studies (~80%) would not meet the assumptions of Random Field Theory and therefore would have reduced sensitivity. Specifically most data is not smooth enough to meet the good lattice assumption. Current studies smooth data on average by twice the voxel size which is rarely sufficient to meet the good lattice assumption. The amount of smoothing required for Random Field Theory to produce accurate p-values increases with image resolution and decreases with degrees of freedom. There is no rule of thumb that is valid for all study designs but for typical data (3mm resolution, and greater than 20 subjects) residual smoothness with FWHM = 4 times voxel size should produce valid results. However, it should be stressed that for higher spatial resolution and lower degrees of freedom the critical smoothness required will increase sharply. This implies that researchers should carefully choose appropriate smoothing kernels. This can be facilitated by the simulations we provide that identify the critical smoothness at which the application of RFT becomes appropriate. For some applications such as presurgical mapping or, imaging of small structures, probing the laminar/columnar structure of the cortex these smoothness requirements may be too great to preserve spatial structure. As such, this study suggests developments are needed in Random Field Theory to fully exploit the resolution of modern neuroimaging.

Published
2016

15. Mouth magnetoencephalography: A unique perspective on the human hippocampus

Author

Tierney, Tim M., Levy, Andrew, Barry, Daniel N., Meyer, Sofie S., Shigihara, Yoshihito, Everatt, Matt, Mellor, Stephanie, Lopez, Jose David, Bestmann, Sven, Holmes, Niall, Roberts, Gillian, Hill, Ryan M, Boto, Elena, Leggett, James, Shah, Vishal, Brookes, Matthew J., Bowtell, Richard, Maguire, Eleanor A., and Barnes, Gareth R.

Published
2021
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20. Magnetoencephalography Using Optically Pumped Magnetometers

Author

Boto, Elena, primary, Holmes, Niall, additional, Tierney, Tim M., additional, Leggett, James, additional, Hill, Ryan, additional, Mellor, Stephanie, additional, Roberts, Gillian, additional, Barnes, Gareth R., additional, Bowtell, Richard, additional, and Brookes, Matthew J., additional

Published
2020
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24. Combining video telemetry and wearable MEG for naturalistic imaging

Author

O'Neill, George C, primary, Seymour, Robert A, additional, Mellor, Stephanie, additional, Alexander, Nicholas, additional, Tierney, Tim M, additional, Bernachot, Lea, additional, Fahimi Hnazee, Mansoureh, additional, Spedden, Meaghan E, additional, Timms, Ryan C, additional, Bestmann, Sven, additional, Brookes, Matthew J, additional, and Barnes, Gareth R, additional

Published
2023
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27. Non-invasive measurements of ictal and interictal epileptiform activity using optically pumped magnetometers

Author

ZL Cerebrovasculaire Ziekten Medisch, Neurologen, Brain, Hillebrand, Arjan, Holmes, Niall, Sijsma, Ndedi, O’Neill, George C., Tierney, Tim M., Liberton, Niels, Stam, Anine H., van Klink, Nicole, Stam, Cornelis J., Bowtell, Richard, Brookes, Matthew J., Barnes, Gareth R., ZL Cerebrovasculaire Ziekten Medisch, Neurologen, Brain, Hillebrand, Arjan, Holmes, Niall, Sijsma, Ndedi, O’Neill, George C., Tierney, Tim M., Liberton, Niels, Stam, Anine H., van Klink, Nicole, Stam, Cornelis J., Bowtell, Richard, Brookes, Matthew J., and Barnes, Gareth R.

Published
2023

31. Improved non-invasive detection of ictal and interictal epileptiform activity using Optically Pumped Magnetometers

Author

Hillebrand, Arjan, primary, Holmes, Niall, additional, Sijsma, Ndedi, additional, O'Neill, George C, additional, Tierney, Tim M, additional, Liberton, Niels, additional, Stam, Anine H, additional, van Klink, Nicole, additional, Stam, Cornelis J, additional, Bowtell, Richard, additional, Brookes, Matthew J, additional, and Barnes, Gareth R, additional

Published
2022
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35. Magnetic Field Mapping and Correction for Moving OP-MEG

Author

Mellor, Stephanie, primary, Tierney, Tim M., additional, O'Neill, George C., additional, Alexander, Nicholas, additional, Seymour, Robert A., additional, Holmes, Niall, additional, Lopez, Jose D., additional, Hill, Ryan M., additional, Boto, Elena, additional, Rea, Molly, additional, Roberts, Gillian, additional, Leggett, James, additional, Bowtell, Richard, additional, Brookes, Matthew J., additional, Maguire, Eleanor A., additional, Walker, Matthew C., additional, and Barnes, Gareth R., additional

Published
2022
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39. Moving magnetoencephalography towards real-world applications with a wearable system

Author

Boto, Elena, Holmes, Niall, Leggett, James, Roberts, Gillian, Shah, Vishal, Meyer, Sofie S., Muoz, Leonardo Duque, Mullinger, Karen J., Tierney, Tim M., Bestmann, Sven, Barnes, Gareth R., Bowtell, Richard, and Brookes, Matthew J.

Subjects
Magnetoencephalography -- Methods -- Equipment and supplies, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Author(s): Elena Boto [1]; Niall Holmes [1]; James Leggett [1]; Gillian Roberts [1]; Vishal Shah [2]; Sofie S. Meyer [3, 4]; Leonardo Duque Muoz [3]; Karen J. Mullinger [1, 5]; [...]

Published
2018
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41. Magnetic Field Mapping and Correction for Moving OP-MEG

Author

Mellor, Stephanie, primary, Tierney, Tim M., additional, O’Neill, George C., additional, Alexander, Nicholas, additional, Seymour, Robert A., additional, Holmes, Niall, additional, López, José D., additional, Hill, Ryan M., additional, Boto, Elena, additional, Rea, Molly, additional, Roberts, Gillian, additional, Leggett, James, additional, Bowtell, Richard, additional, Brookes, Matthew J., additional, Maguire, Eleanor A., additional, Walker, Matthew C., additional, and Barnes, Gareth R., additional

Published
2021
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46. Mouth magnetoencephalography: A unique perspective on the human hippocampus

Author

Tierney, Tim M., primary, Levy, Andrew, additional, Barry, Daniel N., additional, Meyer, Sofie S., additional, Shigihara, Yoshihito, additional, Everatt, Matt, additional, Mellor, Stephanie, additional, Lopez, Jose David, additional, Bestmann, Sven, additional, Holmes, Niall, additional, Roberts, Gillian, additional, Hill, Ryan M, additional, Boto, Elena, additional, Leggett, James, additional, Shah, Vishal, additional, Brookes, Matthew J., additional, Bowtell, Richard, additional, Maguire, Eleanor A., additional, and Barnes, Gareth R., additional

Published
2020
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47. Optically pumped magnetoencephalography in epilepsy

Author

Vivekananda, Umesh, primary, Mellor, Stephanie, additional, Tierney, Tim M., additional, Holmes, Niall, additional, Boto, Elena, additional, Leggett, James, additional, Roberts, Gillian, additional, Hill, Ryan M., additional, Litvak, Vladimir, additional, Brookes, Matthew J., additional, Bowtell, Richard, additional, Barnes, Gareth R., additional, and Walker, Matthew C., additional

Published
2020
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48. Pragmatic spatial sampling for wearable MEG arrays

Author

Tierney, Tim M, primary, Mellor, Stephanie, additional, O’Neill, George C, additional, Holmes, Niall, additional, Boto, Elena, additional, Roberts, Gillian, additional, Hill, Ryan M, additional, Leggett, James, additional, Bowtell, Richard, additional, Brookes, Matthew J, additional, and Barnes, Gareth R, additional

Published
2019
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49. Optically Pumped Magnetoencephalography in Epilepsy

Author

Vivekananda, Umesh, primary, Mellor, Stephanie, additional, Tierney, Tim M, additional, Holmes, Niall, additional, Boto, Elena, additional, Leggett, James, additional, Roberts, Gillian, additional, Hill, Ryan, additional, Litvak, Vladimir, additional, Brookes, Matthew J., additional, Bowtell, Richard, additional, Barnes, Gareth R, additional, and Walker, Matthew C, additional

Published
2019
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50. Data?driven model optimization for optically pumped magnetometer sensor arrays

Author

Tierney, Tim M., Meyer, Sofie S., Boto, Elena, Holmes, Niall, Roberts, Gillian, Leggett, James, Vargas?Bonilla, J. F., Bowtell, Richard, Brookes, Matthew J., and Barnes, Gareth R.

Subjects
Radiological and Ultrasound Technology, Neurology, Radiology Nuclear Medicine and imaging, Clinical Neurology, Anatomy
Abstract

© 2019 The Authors. Human Brain Mapping published by Wiley Periodicals, Inc. Optically pumped magnetometers (OPMs) have reached sensitivity levels that make them viable portable alternatives to traditional superconducting technology for magnetoencephalography (MEG). OPMs do not require cryogenic cooling and can therefore be placed directly on the scalp surface. Unlike cryogenic systems, based on a well-characterised fixed arrays essentially linear in applied flux, OPM devices, based on different physical principles, present new modelling challenges. Here, we outline an empirical Bayesian framework that can be used to compare between and optimise sensor arrays. We perturb the sensor geometry (via simulation) and with analytic model comparison methods estimate the true sensor geometry. The width of these perturbation curves allows us to compare different MEG systems. We test this technique using simulated and real data from SQUID and OPM recordings using head-casts and scanner-casts. Finally, we show that given knowledge of underlying brain anatomy, it is possible to estimate the true sensor geometry from the OPM data themselves using a model comparison framework. This implies that the requirement for accurate knowledge of the sensor positions and orientations a priori may be relaxed. As this procedure uses the cortical manifold as spatial support there is no co-registration procedure or reliance on scalp landmarks.

Published
2019

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