On-scalp magnetoencephalography: Theory, implementation and measurements

Joonas Iivanainen

On-scalp magnetoencephalography: Theory, implementation and measurements

Julkaisun otsikon käännös: Magnetoenkefalografian mittaaminen lähempää aivoja: Teoria ja toteutus

Joonas Iivanainen

Neurotieteen ja lääketieteellisen tekniikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Magnetoenkefalografia (MEG) on kajoamaton aivokuvantamismenetelmä, jossa aivojen sähköisestä toiminnasta syntyvä magneettikenttä mitataan pään ulkopuolella. Tämä neuromagneettinen kenttä sisältää ajallista ja paikallista informaatiota sen synnyttävistä aivolähteistä. Tätä informaatiota voidaan käyttää tulkitsemaan aivoja ja niiden toimintaa. MEG:n ajallinen tarkkuus on erinomainen, sillä magneettikenttä tarjoaa välitöntä informaatiota hermostollisesta aktivaatiosta fysiologisesti merkityksellisellä taajuuskaistalla. MEG:n paikkatarkkuus, tai paikkainformaation määrä, taas on rajoittunut tämänhetkisissä MEG-laitteissa, sillä nykyinen suprajohtava anturitekniikka ei salli magneettikentän mittaamista niin läheltä aivoja kuin vain kajoamattomasti mahdollista: nykyisissä laitteissa magneettikenttä mitataan ainakin kahden senttimetrin päästä pään pinnasta. Tällä etäisyydellä sekä magneettikentän voimakkuus että kentän vapausasteiden lukumäärä ovat kuitenkin jo laskeneet merkittävästi. Kvanttioptiikan kehitys on mahdollistanut magnetoenkefalografiaan soveltuvan anturityypin, jolla pystytään mittaamaan magneettikenttä millimetrien päästä pään pinnasta. Optisesti pumpattujen magnetometrien (OPM) avulla voidaan siis rakentaa pään pinnalla sijaitsevia anturistoja, joiden avulla MEG:n paikkatarkkuutta voidaan parantaa. Väitöskirjassa tutkitaan sekä laskennallisesti että kokeellisesti parannuksia signaalien voimakkuuksissa sekä mittauksen paikkatarkkuudessa, kun magneettikenttä mitataan pään pinnalla. Työssä tutkitaan teoreettisesti vaatimuksia magneettikentän näytteistämiselle paikan suhteen näiden parannusten saavuttamiseksi. Väitöskirjassa rakennetaan MEG-laitteisto, jossa OPM-antureita käytetään mittaamaan aivojen magneettikenttä suoraan pään pinnalta. Laitteisto käyttää aktiivista suojausta magneettisten häiriöiden vähentämiseksi. Systeemillä mitataan näköaivokuoren neuromagneettisia vasteita ja näitä vasteita verrataan suprajohtavilla antureilla mitattuihin. Väitöskirja näyttää OPM:iin pohjautuvien anturistojen potentiaalin magnetoenkefalografiassa sekä yleisesti että sen paikkatarkkuuden parantamisessa.

Julkaisun otsikon käännös	Magnetoenkefalografian mittaaminen lähempää aivoja: Teoria ja toteutus
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Parkkonen, Lauri, Vastuuprofessori Parkkonen, Lauri, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-8990-4
Sähköinen ISBN	978-952-60-8991-1
Tila	Julkaistu - 2020
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

magnetoenkefalografia
optisesti pumpattu magnetometri
magneettinen suojaus
aivokuvantaminen
näytteistys

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-8991-1

Aalto NeuroImaging Infrastructure
Jousmäki, V. (Manager)
Perustieteiden korkeakoulu
Laitteistot/tilat: Facility
Science-IT
Hakala, M. (Manager)
Perustieteiden korkeakoulu
Laitteistot/tilat: Facility

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@phdthesis{cf10d2212167466d8ce893d357805e75,

title = "On-scalp magnetoencephalography: Theory, implementation and measurements",

abstract = "Magnetoencephalography (MEG) is a noninvasive neuroimaging technique in which the magnetic fields of electrically active neuron populations in the brain are measured outside the head. The neuromagnetic field contains temporal and spatial information about the underlying neuronal sources. Measurements of this field can be used to make inference about brain function. The temporal resolution of MEG is excellent as the magnetic field gives an instantaneous measure of the neuronal activity at the physiologically relevant frequency range. However, the spatial resolution, or the amount of spatial information, is limited in the state-of-the-art MEG systems as the current superconducting sensor technology does not allow the field measurement as close to the neural sources as noninvasively possible but limits the measurement distance to a couple of centimeters from the subject's scalp. At that distance, the field amplitude as well as the number of spatial degrees of freedom in the field have decayed considerably. Recent developments in quantum optics have enabled sensors suitable for measuring the neuromagnetic field within millimetres from the scalp. With these optically-pumped magnetometers (OPMs), on-scalp sensor arrays can be constructed increasing the spatial resolution of MEG. In this Thesis, improvement in signal amplitude as well as in spatial resolution due to on-scalp field sensing is quantified both with simulations and measurements. Requirements for spatial sampling of the neuromagnetic field to achieve those improvements are theoretically investigated. To sense the neuromagnetic field on scalp, an OPM-based MEG system is constructed. The system uses active magnetic shielding with external coils to reduce interference in the measurements. Neuromagnetic responses to visual stimulation are measured using the OPM system and are compared to those obtained with a state-of-the-art cryogenic MEG system. The Thesis shows the potential of on-scalp sensor arrays implemented with OPMs to increase the spatial resolution and applicability of MEG.",

keywords = "magnetoencephalography, optically-pumped magnetometer, on scalp, magnetic shielding, neuroimaging, sampling, magnetoenkefalografia, optisesti pumpattu magnetometri, magneettinen suojaus, aivokuvantaminen, n{\"a}ytteistys, magnetoencephalography, optically-pumped magnetometer, on scalp, magnetic shielding, neuroimaging, sampling",

author = "Joonas Iivanainen",

year = "2020",

language = "English",

isbn = "978-952-60-8990-4",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "38",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - On-scalp magnetoencephalography: Theory, implementation and measurements

AU - Iivanainen, Joonas

PY - 2020

Y1 - 2020

N2 - Magnetoencephalography (MEG) is a noninvasive neuroimaging technique in which the magnetic fields of electrically active neuron populations in the brain are measured outside the head. The neuromagnetic field contains temporal and spatial information about the underlying neuronal sources. Measurements of this field can be used to make inference about brain function. The temporal resolution of MEG is excellent as the magnetic field gives an instantaneous measure of the neuronal activity at the physiologically relevant frequency range. However, the spatial resolution, or the amount of spatial information, is limited in the state-of-the-art MEG systems as the current superconducting sensor technology does not allow the field measurement as close to the neural sources as noninvasively possible but limits the measurement distance to a couple of centimeters from the subject's scalp. At that distance, the field amplitude as well as the number of spatial degrees of freedom in the field have decayed considerably. Recent developments in quantum optics have enabled sensors suitable for measuring the neuromagnetic field within millimetres from the scalp. With these optically-pumped magnetometers (OPMs), on-scalp sensor arrays can be constructed increasing the spatial resolution of MEG. In this Thesis, improvement in signal amplitude as well as in spatial resolution due to on-scalp field sensing is quantified both with simulations and measurements. Requirements for spatial sampling of the neuromagnetic field to achieve those improvements are theoretically investigated. To sense the neuromagnetic field on scalp, an OPM-based MEG system is constructed. The system uses active magnetic shielding with external coils to reduce interference in the measurements. Neuromagnetic responses to visual stimulation are measured using the OPM system and are compared to those obtained with a state-of-the-art cryogenic MEG system. The Thesis shows the potential of on-scalp sensor arrays implemented with OPMs to increase the spatial resolution and applicability of MEG.

AB - Magnetoencephalography (MEG) is a noninvasive neuroimaging technique in which the magnetic fields of electrically active neuron populations in the brain are measured outside the head. The neuromagnetic field contains temporal and spatial information about the underlying neuronal sources. Measurements of this field can be used to make inference about brain function. The temporal resolution of MEG is excellent as the magnetic field gives an instantaneous measure of the neuronal activity at the physiologically relevant frequency range. However, the spatial resolution, or the amount of spatial information, is limited in the state-of-the-art MEG systems as the current superconducting sensor technology does not allow the field measurement as close to the neural sources as noninvasively possible but limits the measurement distance to a couple of centimeters from the subject's scalp. At that distance, the field amplitude as well as the number of spatial degrees of freedom in the field have decayed considerably. Recent developments in quantum optics have enabled sensors suitable for measuring the neuromagnetic field within millimetres from the scalp. With these optically-pumped magnetometers (OPMs), on-scalp sensor arrays can be constructed increasing the spatial resolution of MEG. In this Thesis, improvement in signal amplitude as well as in spatial resolution due to on-scalp field sensing is quantified both with simulations and measurements. Requirements for spatial sampling of the neuromagnetic field to achieve those improvements are theoretically investigated. To sense the neuromagnetic field on scalp, an OPM-based MEG system is constructed. The system uses active magnetic shielding with external coils to reduce interference in the measurements. Neuromagnetic responses to visual stimulation are measured using the OPM system and are compared to those obtained with a state-of-the-art cryogenic MEG system. The Thesis shows the potential of on-scalp sensor arrays implemented with OPMs to increase the spatial resolution and applicability of MEG.

KW - magnetoencephalography

KW - optically-pumped magnetometer

KW - on scalp

KW - magnetic shielding

KW - neuroimaging

KW - sampling

KW - magnetoenkefalografia

KW - optisesti pumpattu magnetometri

KW - magneettinen suojaus

KW - aivokuvantaminen

KW - näytteistys

KW - magnetoencephalography

KW - optically-pumped magnetometer

KW - on scalp

KW - magnetic shielding

KW - neuroimaging

KW - sampling

M3 - Doctoral Thesis

SN - 978-952-60-8990-4

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

On-scalp magnetoencephalography: Theory, implementation and measurements

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

Laitteet

Aalto NeuroImaging Infrastructure

Science-IT

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