Flexible High Performance Magnetic Field Sensors: On-Scalp Magnetoencephalography and Other Applications

Preface
Contents
About the Editors
Part I OPM and System Developments
1 Optically Pumped Magnetometers for Biomagnetic Measurements
1.1 Introduction
1.2 General Features of Atomic Magnetometer Operation
1.3 Sensitivity of Atomic Magnetometers
1.4 Alkali-Metal Atomic Magnetometers
1.4.1 Spin-Exchange Relaxation-Free Alkali-Metal Magnetometers
1.5 Practical Challenges in Operation of Atomic Magnetometers
1.6 Conclusions
References
2 Optically Pumped Magnetometers Compatible with Large Transient Magnetic Fields
2.1 Introduction
2.1.1 Brief Introduction to SERF OPMs
2.2 Methods for Stable Operation in a Noisy Environment
2.2.1 Closed-Loop Mode
2.2.2 Magnetic Gradiometry
2.3 Transcranial Magnetic Stimulation
2.4 Conclusion
References
3 Small Animal Biomagnetism Applications
3.1 Introduction
3.1.1 High Sensitivity Optically Pumped Magnetometers for Biomagnetic Recordings
3.1.2 Why Biomagnetic Recordings on Small Animals?
3.1.3 Examples of Animal Biomagnetic Recordings
3.1.4 Ethics and Legislation
3.2 Optically Pumped Magnetometer
3.3 Biomagnetic Recordings
3.3.1 Detection of Nerve Impulses
3.3.2 Cardiology Applications
3.3.3 Towards Imaging the Electrical Conductivity of the Heart
3.4 Conclusions
References
4 Supine OPM-MEG in Multilayer Cylindrical Shield
4.1 Introduction
4.2 Multichannel OPM Array
4.2.1 All-Optical OPM and Sensitivity
4.2.2 Multichannel Control System
4.3 Multilayer Cylindrical Shield
4.3.1 Magnetic Shielding for MEG
4.3.2 Finite Element Method
4.3.3 Performance of a Four-Layer Cylindrical Shield
4.4 Sensor-to-Brain Co-registration and Source Imaging
4.4.1 Sensor Localization and Co-registration
4.4.2 Multichannel Detection and Source Imaging
4.5 Summary and Future Work
References
5 Ambulatory MEG Arrays
5.1 Introduction
5.2 Background
5.3 OPM Arrays
5.4 OPM Helmet
5.5 Sensor Connections and Cable Management
5.6 Triaxial Operation
5.7 Electronics Miniaturization
5.8 System Architecture
5.9 Discussion and Future Outlook
References
Part II MEG Applications
6 Tri-axial Helium-4 Optically Pumped Magnetometers for MEG
6.1 Introduction
6.2 Helium Magnetometers for Space Exploration
6.3 Helium Magnetometers Transfer to Biomedical Imaging
6.3.1 Optically Pumped Magnetometers Based on Atomic Alignment
6.3.2 The Evolution of Aligned States in Parametric Resonance Magnetometers
6.4 First Demonstration of MCG
6.4.1 Phantom Measurement
6.4.2 MCG Measurements on Healthy Volunteers
6.5 First Demonstration of MEG
6.5.1 Simulated MEG Signals from a Brain Phantom
6.5.2 MEG Recordings on a Healthy Subject
6.6 An Array of Second-Generation Helium Magnetometers
6.6.1 Probe Configuration
6.6.2 Sensitivity and Bandwidth in Open-Loop Operation
6.6.3 Closed-Loop Operation: Principle and Intrinsic Noise
6.6.4 Correcting the Cross-Talks in Closed-Loop Operation
6.7 Alternative Magnetometer Configurations Based on Aligned Ensembles of Metastable Helium-4
6.7.1 An All-Optical Magnetometer Based on Hanle Effect on an Aligned Atomic Ensemble
6.7.2 A Parametric Resonance Magnetometer Based Both on Atomic Orientation and Alignment
6.8 Conclusion
References
7 Person-Sized Magnetoencephalography Systems with Optically Pumped Magnetometers
7.1 Introduction
7.2 Magnetic Shielding
7.2.1 Design of Our Person-Sized Shield
7.2.2 Magnetic Field Control Within the Shield
7.3 The Optically Pumped Magnetometer
7.3.1 OPM Design
7.3.2 Importance of Magnetic Field Control
7.3.3 The OPM-MEG System
7.3.4 Laser System
7.3.5 Temperature Controller
7.3.6 Signal Detection
7.3.7 Magnetic Field Generation
7.4 Testing with Human Subjects
7.4.1 Stimuli Presentation
7.4.2 Signal Processing Pipeline
7.4.2.1 Magnetoencephalography Data Processing
7.4.2.2 Constructing the Forward Model
7.4.2.3 Neuronal Current Source Localization
7.4.3 Magnetoencephalography Results
7.5 Conclusion
References
8 On-scalp MEG with High-Tc SQUIDs
8.1 Introduction
8.2 High-Tc SQUID Sensitivity
8.3 Spatial Sampling Theory: Maximizing the On-scalp Benefit
8.4 System Design Considerations
8.5 Technical Developments Toward Practical On-scalp MEG Measurements
8.6 Experimental Demonstrations of High-Tc SQUID-based On-scalp MEG Advantages
8.7 Conclusions and Future Prospects
References
9 Fiber-Coupled OPM in Purely Coil-Shielded Environment
9.1 Introduction
9.2 Bell-Bloom Atomic Magnetometer
9.3 Active Magnetic Field Stabilization
9.4 Unshielded MEG Measurements
9.5 Conclusions and Outlook
References
10 SERF-OPM Usability for MEG in Two-Layer-Shielded Rooms
10.1 Introduction
10.2 SERF-OPM-MEG Setup in a Two-Layer Actively Shielded Room
10.3 SERF-OPM Signal Characteristics in Empty Room
10.4 OPM-MEG Feasibility Demonstration with Subjects
10.5 Source Localization Comparison of OPM- and SQUID-MEG Data
10.6 Discussion and Conclusion
References
11 Turning OPM-MEG into a Wearable Technology
11.1 Introduction
11.1.1 An Overview of Conventional MEG
11.1.2 Why OPMs Are the Stand-Out Replacement
11.2 Technical Challenges
11.2.1 What an OPM for MEG Should Look Like
11.2.1.1 Single Axis vs Triaxial
11.2.1.2 Magnetometer vs. Gradiometer
11.2.1.3 Nascent OPM Designs
11.2.2 Designing OPM Sensor Arrays for MEG
11.2.2.1 Region-Specific OPM-MEG Arrays
11.2.2.2 Fixed or Wearable Arrays
11.2.2.3 3D-Printed Individual Scanner Casts
11.2.2.4 Generic Caps and Helmets
11.2.2.5 Crosstalk
11.2.3 Suppressing Background Magnetic Fields
11.2.3.1 Magnetically Shielded Environments
11.2.3.2 Using Coils to Null the Static Remnant Magnetic Field
11.2.3.3 Nulling Dynamic Magnetic Fields
11.3 Applications
11.3.1 Novel Paradigms
11.3.2 New Subject Cohorts
11.3.3 Creative Sensor Placement
11.4 Conclusion and Future Outlook
References
Part III MCG, MRX, and Other Applications
12 OPM Gradiometer for Magnetorelaxometry
12.1 Introduction
12.1.1 Magnetic Nanoparticles and Relaxation
12.1.2 Magnetorelaxometry Principles
12.1.3 Application of MNP Relaxation to Biological Processes
12.2 Development of a System for Magnetorelaxometry in Samples and Small Animals
12.3 State of the Art and Perspectives
12.4 Conclusion
References
13 Unshielded High-Bandwidth Magnetorelaxometry of Magnetic Nanoparticles with Optically PumpedMagnetometers
13.1 Introduction
13.2 The Need for High Bandwidth in MRX
13.3 OPM Operation Modes for High Bandwidth and Unshielded Operation
13.4 MRX with Feedback-Controlled OPMs in Weakly Shielded Environments
13.5 Free Spin Precession OPM
13.6 Unshielded MRX with a Commercially Available Free Spin Precession OPM
13.7 Conclusion and Outlook
References
14 Adult Magnetocardiography: Principles and Clinical Practice
14.1 Introduction
14.2 Implementation of OPM-MCG
14.2.1 Hardware Overview and Common Practice
14.2.2 Data Analysis
14.3 Adult Magnetocardiography in Clinical Practice: A Review of SQUID and OPM Paradigms and Analysis
References
15 Fetal Magnetocardiography with OPMs
15.1 Overview of fMCG
15.2 fMCG System Design Considerations
15.2.1 fMCG Signal Characteristics
15.2.2 fMCG System Components
15.2.2.1 Magnetic Sensors
15.2.2.2 Magnetic Shielding
15.2.2.3 Signal Processing Techniques
15.3 A Prototype OPM fMCG System
15.3.1 Person-Sized Shield
15.3.2 OPM Sensor Array
15.3.3 Performance Assessment
15.3.3.1 Signal-to-Noise Ratio
15.3.3.2 Diagnostic Information
15.3.3.3 Subject Comfort
15.4 Conclusions
15.5 Future Directions
References
16 Emerging MR Sensors for Biomagnetic Measurements
16.1 Magnetoresistive Device-Based Magnetic Flux Sensors
16.2 Calibration of Sensor Array
16.3 Magnetocardiographic Measurements by MR Sensors
16.4 Magnetoneurographic Measurements by MR Sensors
16.5 Conclusion
References
Index