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Zahran S, Mahmoudzadeh M, Wallois F, Betrouni N, Derambure P, Le Prado M, Palacios-Laloy A, Labyt E. Performance Analysis of Optically Pumped 4He Magnetometers vs. Conventional SQUIDs: From Adult to Infant Head Models. SENSORS (BASEL, SWITZERLAND) 2022; 22:s22083093. [PMID: 35459077 PMCID: PMC9024855 DOI: 10.3390/s22083093] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 03/30/2022] [Accepted: 04/08/2022] [Indexed: 05/27/2023]
Abstract
Optically pumped magnetometers (OPMs) are new, room-temperature alternatives to superconducting quantum interference devices (SQUIDs) for measuring the brain's magnetic fields. The most used OPM in MagnetoEncephaloGraphy (MEG) are based on alkali atoms operating in the spin-exchange relaxation-free (SERF) regime. These sensors do not require cooling but have to be heated. Another kind of OPM, based on the parametric resonance of 4He atoms are operated at room temperature, suppressing the heat dissipation issue. They also have an advantageous bandwidth and dynamic range more suitable for MEG recordings. We quantitatively assessed the improvement (relative to a SQUID magnetometers array) in recording the magnetic field with a wearable 4He OPM-MEG system through data simulations. The OPM array and magnetoencephalography forward models were based on anatomical MRI data from an adult, a nine-year-old child, and 10 infants aged between one month and two years. Our simulations showed that a 4He OPMs array offers markedly better spatial specificity than a SQUID magnetometers array in various key performance areas (e.g., signal power, information content, and spatial resolution). Our results are also discussed regarding previous simulation results obtained for alkali OPM.
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Affiliation(s)
- Saeed Zahran
- INSERM, U1105, GRAMFC, Université de Picardie Jules Verne, CHU Sud, 80000 Amiens, France; (S.Z.); (M.M.); (F.W.)
| | - Mahdi Mahmoudzadeh
- INSERM, U1105, GRAMFC, Université de Picardie Jules Verne, CHU Sud, 80000 Amiens, France; (S.Z.); (M.M.); (F.W.)
| | - Fabrice Wallois
- INSERM, U1105, GRAMFC, Université de Picardie Jules Verne, CHU Sud, 80000 Amiens, France; (S.Z.); (M.M.); (F.W.)
| | - Nacim Betrouni
- INSERM, U1172, CHU de Lille, Université de Lille, Degenerative & Vascular Cognitive Disorders, 59000 Lille, France; (N.B.); (P.D.)
| | - Philippe Derambure
- INSERM, U1172, CHU de Lille, Université de Lille, Degenerative & Vascular Cognitive Disorders, 59000 Lille, France; (N.B.); (P.D.)
| | - Matthieu Le Prado
- Laboratoire d’Electronique et de Technologies de l’Information, CEA, 38054 Grenoble, France; (M.L.P.); (A.P.-L.)
- Mag4health, 9 Avenue Paul Verlaine, 38000 Grenoble, France
| | - Agustin Palacios-Laloy
- Laboratoire d’Electronique et de Technologies de l’Information, CEA, 38054 Grenoble, France; (M.L.P.); (A.P.-L.)
| | - Etienne Labyt
- Laboratoire d’Electronique et de Technologies de l’Information, CEA, 38054 Grenoble, France; (M.L.P.); (A.P.-L.)
- CEA Tech Hauts de France, 59000 Lille, France
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Marhl U, Jodko-Władzińska A, Brühl R, Sander T, Jazbinšek V. Transforming and comparing data between standard SQUID and OPM-MEG systems. PLoS One 2022; 17:e0262669. [PMID: 35045107 PMCID: PMC8769297 DOI: 10.1371/journal.pone.0262669] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Accepted: 01/03/2022] [Indexed: 11/18/2022] Open
Abstract
Optically pumped magnetometers (OPMs) have recently become so sensitive that they are suitable for use in magnetoencephalography (MEG). These sensors solve operational problems of the current standard MEG, where superconducting quantum interference device (SQUID) gradiometers and magnetometers are being used. The main advantage of OPMs is that they do not require cryogenics for cooling. Therefore, they can be placed closer to the scalp and are much easier to use. Here, we measured auditory evoked fields (AEFs) with both SQUID- and OPM-based MEG systems for a group of subjects to better understand the usage of a limited sensor count OPM-MEG. We present a theoretical framework that transforms the within subject data and equivalent simulation data from one MEG system to the other. This approach works on the principle of solving the inverse problem with one system, and then using the forward model to calculate the magnetic fields expected for the other system. For the source reconstruction, we used a minimum norm estimate (MNE) of the current distribution. Two different volume conductor models were compared: the homogeneous conducting sphere and the three-shell model of the head. The transformation results are characterized by a relative error and cross-correlation between the measured and the estimated magnetic field maps of the AEFs. The results for both models are encouraging. Since some commercial OPMs measure multiple components of the magnetic field simultaneously, we additionally analyzed the effect of tangential field components. Overall, our dual-axis OPM-MEG with 15 sensors yields similar information to a 62-channel SQUID-MEG with its field of view restricted to the right hemisphere.
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Affiliation(s)
- Urban Marhl
- Institute of Mathematics, Physics and Mechanics, Ljubljana, Slovenia
- Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor, Slovenia
- * E-mail:
| | - Anna Jodko-Władzińska
- Warsaw University of Technology, Warsaw, Poland
- Physikalisch-Technische Bundesanstalt, Berlin, Germany
| | - Rüdiger Brühl
- Physikalisch-Technische Bundesanstalt, Berlin, Germany
| | | | - Vojko Jazbinšek
- Institute of Mathematics, Physics and Mechanics, Ljubljana, Slovenia
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Triaxial detection of the neuromagnetic field using optically-pumped magnetometry: feasibility and application in children. Neuroimage 2022; 252:119027. [PMID: 35217205 PMCID: PMC9135302 DOI: 10.1016/j.neuroimage.2022.119027] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Revised: 01/11/2022] [Accepted: 02/21/2022] [Indexed: 12/02/2022] Open
Abstract
Optically-pumped magnetometers (OPMs) are an established alternative to superconducting sensors for magnetoencephalography (MEG), offering significant advantages including flexibility to accommodate any head size, uniform coverage, free movement during scanning, better data quality and lower cost. However, OPM sensor technology remains under development; there is flexibility regarding OPM design and it is not yet clear which variant will prove most effective for MEG. Most OPM-MEG implementations have either used single-axis (equivalent to conventional MEG) or dual-axis magnetic field measurements. Here we demonstrate use of a triaxial OPM formulation, able to characterise the full 3D neuromagnetic field vector. We show that this novel sensor is able to characterise magnetic fields with high accuracy and sensitivity that matches conventional (dual-axis) OPMs. We show practicality via measurement of biomagnetic fields from both the heart and the brain. Using simulations, we demonstrate how triaxial measurement offers improved cortical coverage, especially in infants. Finally, we introduce a new 3D-printed child-friendly OPM-helmet and demonstrate feasibility of triaxial measurement in a five-year-old. In sum, the data presented demonstrate that triaxial OPMs offer a significant improvement over dual-axis variants and are likely to become the sensor of choice for future MEG systems, particularly for deployment in paediatric populations.
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Theoretical advantages of a triaxial optically pumped magnetometer magnetoencephalography system. Neuroimage 2021; 236:118025. [PMID: 33838266 PMCID: PMC8249355 DOI: 10.1016/j.neuroimage.2021.118025] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 02/10/2021] [Accepted: 03/25/2021] [Indexed: 01/10/2023] Open
Abstract
The optically pumped magnetometer (OPM) is a viable means to detect magnetic fields generated by human brain activity. Compared to conventional detectors (superconducting quantum interference devices) OPMs are small, lightweight, flexible, and operate without cryogenics. This has led to a step change in instrumentation for magnetoencephalography (MEG), enabling a "wearable" scanner platform, adaptable to fit any head size, able to acquire data whilst subjects move, and offering improved data quality. Although many studies have shown the efficacy of 'OPM-MEG', one relatively untapped advantage relates to improved array design. Specifically, OPMs enable the simultaneous measurement of magnetic field components along multiple axes (distinct from a single radial orientation, as used in most conventional MEG systems). This enables characterisation of the magnetic field vector at all sensors, affording extra information which has the potential to improve source reconstruction. Here, we conduct a theoretical analysis of the critical parameters that should be optimised for effective source reconstruction. We show that these parameters can be optimised by judicious array design incorporating triaxial MEG measurements. Using simulations, we demonstrate how a triaxial array offers a dramatic improvement on our ability to differentiate real brain activity from sources of magnetic interference (external to the brain). Further, a triaxial system is shown to offer a marked improvement in the elimination of artefact caused by head movement. Theoretical results are supplemented by an experimental recording demonstrating improved interference reduction. These findings offer new insights into how future OPM-MEG arrays can be designed with improved performance.
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Lau S, Güllmar D, Flemming L, Grayden DB, Cook MJ, Wolters CH, Haueisen J. Skull Defects in Finite Element Head Models for Source Reconstruction from Magnetoencephalography Signals. Front Neurosci 2016; 10:141. [PMID: 27092044 PMCID: PMC4823312 DOI: 10.3389/fnins.2016.00141] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 03/18/2016] [Indexed: 11/24/2022] Open
Abstract
Magnetoencephalography (MEG) signals are influenced by skull defects. However, there is a lack of evidence of this influence during source reconstruction. Our objectives are to characterize errors in source reconstruction from MEG signals due to ignoring skull defects and to assess the ability of an exact finite element head model to eliminate such errors. A detailed finite element model of the head of a rabbit used in a physical experiment was constructed from magnetic resonance and co-registered computer tomography imaging that differentiated nine tissue types. Sources of the MEG measurements above intact skull and above skull defects respectively were reconstructed using a finite element model with the intact skull and one incorporating the skull defects. The forward simulation of the MEG signals reproduced the experimentally observed characteristic magnitude and topography changes due to skull defects. Sources reconstructed from measured MEG signals above intact skull matched the known physical locations and orientations. Ignoring skull defects in the head model during reconstruction displaced sources under a skull defect away from that defect. Sources next to a defect were reoriented. When skull defects, with their physical conductivity, were incorporated in the head model, the location and orientation errors were mostly eliminated. The conductivity of the skull defect material non-uniformly modulated the influence on MEG signals. We propose concrete guidelines for taking into account conducting skull defects during MEG coil placement and modeling. Exact finite element head models can improve localization of brain function, specifically after surgery.
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Affiliation(s)
- Stephan Lau
- Institute of Biomedical Engineering and Informatics, Technical University IlmenauIlmenau, Germany; Department of Neurology, Biomagnetic Center, University Hospital JenaJena, Germany; NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of MelbourneParkville, VIC, Australia; Centre for Neural Engineering, University of MelbourneParkville, VIC, Australia; Department of Medicine - St. Vincent's Hospital, University of MelbourneFitzroy, VIC, Australia
| | - Daniel Güllmar
- Medical Physics Group, Department of Diagnostic and Interventional Radiology, University Hospital Jena Jena, Germany
| | - Lars Flemming
- Department of Neurology, Biomagnetic Center, University Hospital Jena Jena, Germany
| | - David B Grayden
- NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of MelbourneParkville, VIC, Australia; Centre for Neural Engineering, University of MelbourneParkville, VIC, Australia
| | - Mark J Cook
- Department of Medicine - St. Vincent's Hospital, University of Melbourne Fitzroy, VIC, Australia
| | - Carsten H Wolters
- Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster Münster, Germany
| | - Jens Haueisen
- Institute of Biomedical Engineering and Informatics, Technical University Ilmenau Ilmenau, Germany
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Götz T, Milde T, Curio G, Debener S, Lehmann T, Leistritz L, Witte OW, Witte H, Haueisen J. Primary somatosensory contextual modulation is encoded by oscillation frequency change. Clin Neurophysiol 2015; 126:1769-79. [PMID: 25670344 DOI: 10.1016/j.clinph.2014.12.028] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Revised: 11/14/2014] [Accepted: 12/01/2014] [Indexed: 10/24/2022]
Abstract
OBJECTIVE This study characterized thalamo-cortical communication by assessing the effect of context-dependent modulation on the very early somatosensory evoked high-frequency oscillations (HF oscillations). METHODS We applied electrical stimuli to the median nerve together with an auditory oddball paradigm, presenting standard and deviant target tones representing differential cognitive contexts to the constantly repeated electrical stimulation. Median nerve stimulation without auditory stimulation served as unimodal control. RESULTS A model consisting of one subcortical (near thalamus) and two cortical (Brodmann areas 1 and 3b) dipolar sources explained the measured HF oscillations. Both at subcortical and the cortical levels HF oscillations were significantly smaller during bimodal (somatosensory plus auditory) than unimodal (somatosensory only) stimulation. A delay differential equation model was developed to investigate interactions within the 3-node thalamo-cortical network. Importantly, a significant change in the eigenfrequency of Brodmann area 3b was related to the context-dependent modulation, while there was no change in the network coupling. CONCLUSION This model strongly suggests cortico-thalamic feedback from both cortical Brodmann areas 1 and 3b to the thalamus. With the 3-node network model, thalamo-cortical feedback could be described. SIGNIFICANCE Frequency encoding plays an important role in contextual modulation in the somatosensory thalamo-cortical network.
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Affiliation(s)
- T Götz
- Biomagnetic Center, Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; Center for Sepsis Control and Care, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany
| | - T Milde
- Institute of Medical Statistics, Computer Sciences and Documentation, Jena University Hospital, Bachstrasse 18, 07740 Jena, Germany
| | - G Curio
- Neurophysics Group, Department of Neurology, Campus Benjamin Franklin, Charité - University Medicine Berlin, Hindenburgdamm 30, 12200 Berlin, Germany
| | - S Debener
- Faculty VI, Department of Psychology, Neuropsychology Lab, University of Oldenburg, 26111 Oldenburg, Germany
| | - T Lehmann
- Institute of Medical Statistics, Computer Sciences and Documentation, Jena University Hospital, Bachstrasse 18, 07740 Jena, Germany
| | - L Leistritz
- Institute of Medical Statistics, Computer Sciences and Documentation, Jena University Hospital, Bachstrasse 18, 07740 Jena, Germany
| | - O W Witte
- Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; Center for Sepsis Control and Care, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany
| | - H Witte
- Institute of Medical Statistics, Computer Sciences and Documentation, Jena University Hospital, Bachstrasse 18, 07740 Jena, Germany
| | - J Haueisen
- Biomagnetic Center, Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; Institute of Biomedical Engineering and Informatics, Faculty of Computer Science and Automation, Technical University Ilmenau, Gustav-Kirchhoff-Straße 2, 98693 Ilmenau, Germany.
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Nurminen J, Taulu S, Nenonen J, Helle L, Simola J, Ahonen A. Improving MEG Performance With Additional Tangential Sensors. IEEE Trans Biomed Eng 2013; 60:2559-66. [DOI: 10.1109/tbme.2013.2260541] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Radial and tangential components of dipolar sources and their magnetic fields. Clin Neurophysiol 2012; 123:1477-8. [PMID: 22321297 DOI: 10.1016/j.clinph.2012.01.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 01/10/2012] [Accepted: 01/10/2012] [Indexed: 11/22/2022]
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