2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 1 Development of Complex Curricula for Molecular Bionics and Infobionics Programs within a consortial* framework** Consortium leader PETER PAZMANY CATHOLIC UNIVERSITY Consortium members SEMMELWEIS UNIVERSITY, DIALOG CAMPUS PUBLISHER The Project has been realised with the support of the European Union and has been co-financed by the European Social Fund *** **Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben ***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg. PETER PAZMANY CATHOLIC UNIVERSITY SEMMELWEIS UNIVERSITY sote_logo.jpg dk_fejlec.gif INFOBLOKK 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2 Peter Pazmany Catholic University Faculty of Information Technology ELECTROPHYSIOLOGICAL METHODS OF THE STUDY OF THE NERVOUS-AND MUSCULAR SYSTEM LECTURE10 MAGNETOENCEPHALOGRAPHY www.itk.ppke.hu Az ideg-és izomrendszer elektrofiziológiai vizsgálómódszerei (Magnetoenkefalográfia) BALÁZS DOMBOVÁRIand GYÖRGY KARMOS Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 3 • Inthislecturethestudentswilllearn:– Definitionof magnetoencephalography – The originof theMEG signal – The basicfunctionof MEG – The basicequipmentsforMEG measures. – Howdoesa typicalMEG rawdatalooklike – Sourcelocalizationof MEG – Temporaland spatialresolutionof MEG – Somefeatures/benefitsof MEG – Research and clinicalapplications www.itk.ppke.hu Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 4 Magnetoencephalography(MEG): isanon-invasiveneurophysiologicalimagingtechniquethatmeasuresthemagneticfieldsgeneratedbyneuronalactivityofthebrain. MEGisadirectmeasureofbrainfunction,unlikefunctionalmeasuressuchasfMRI,PETandSPECTthataresecondarymeasuresofbrainfunctionreflectingbrainmetabolism. TheMEGwasfirstmeasuredbyUniversityofIllinoisphysicistDavidCohenin1968,usingonlyacopperinductioncoilasthedetector. www.itk.ppke.hu Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 5 THE ORIGINOF THEMEG SIGNAL MEGcanestimateelectricalactivityinthebrainfromsensorsoutsidethehead(dots).Thered/blueregionsshowareasofthecortextowhichMEGismost/leastsensitive. www.itk.ppke.hu Sensitivity.jpg Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 6 THE ORIGINOF THEMEG SIGNAL TheMEG(andEEG)signalsderivefromtheneteffectofioniccurrentsflowinginthedendritesofneuronsduringsynaptictransmission. www.itk.ppke.hu http://images1.wikia.nocookie.net/__cb20060309082121/psychology/images/0/0e/Magnetoencephalography.png InaccordancewithMaxwell'sequations,anyelectricalcurrentwillproduceanorthogonallyorientedmagneticfield.ThisfieldismeasuredwithMEG. Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 7 THE ORIGINOF THEMEG SIGNAL Thenetcurrentscanbethoughtofascurrentdipoleswhicharecurrentsdefinedtohaveanassociatedposition,orientation,andmagnitude,butnospatialextent. Accordingtotheright-handrule,acurrentdipolegivesrisetoamagneticfieldthatflowsaroundtheaxisofitsvectorcomponent. www.itk.ppke.hu Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 8 SUPERCONDUCTINGQUANTUMINTERFERENCEDEVICE Themagneticfieldsoutsidetheheadduetoelectricalactivitywithinthebrainareinthehundredsoffemto(10-15)Tesla,thatisapproximately100milliontimesmallerthantheearth'smagneticfield. MEGmeasurementsareconductedexternally,usinganextremelysensitivedevicecalledasuperconductingquantuminterferencedevice(SQUID,Clarke1994). Thesedevicesconvertthesub-quantachangesinmagneticfluxintovoltagechanges. MAGNETICFIELDS Tesla 10-4 HEARTH(STEADY) 10-5 10-6µT URBAN NOISE 10-7 10-8 LUNGPARTICLES 10-9 nT HUMAN HEART 10-10 HUMAN SKELETALMUSCLE FETALHEART 10-11 HUMAN EYE(STEADY) HUMAN BRAIN(ALPHA) 10-12pT HUMAN BRAINRESONSE 10-13 10-14 SQUIDNOISE 10-15fT Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 9 MEASUREMENTWITHMEG TypicallytheSQUIDsarecoupledtosuperconductingcoilsorfluxtransformerswhicharesituatedascloseaspossibletothesubject'shead(within2cmtypically). MagneticfieldchangesinthefluxtransformerscauseachangeinsuperconductingcurrentinthetransformercoilsthatispassedviaaninputcoiltotheSQUIDitself. Theabilitytomeasuresuchsmallfieldsalsomakesthedevicesverysensitivetoothermagneticfieldchangesintheenvironment. ElektaNeuromagTRIUX www.elekta.com C:\Documents and Settings\gkarmos\Desktop\MEG\sendbinary.aspx Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 10 SCHEMATICDIAGRAM OF A MEG Gradiomet2.jpg Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 11 ElektaNeuromagTRIUX C:\Documents and Settings\gkarmos\Desktop\MEG\sendbinary (1).aspx C:\Documents and Settings\gkarmos\Desktop\MEG\sendbinary (2).aspx G:\TÁMOP_PROSTH\steretoax_anyag\elekta\logo.jpg www.elekta.com Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 12 In a modern MEG device, an array of more than 300 SQUIDS is contained in a helmet shaped liquid helium containing vessel called a Dewar, allowing simultaneous measurements at many points over the head. The MEG system is operated in a shielded room that minimizes interference from external magnetic disturbances, including the Earth’s magnetic field, noise generated by electrical equipment, radiofrequency signals, and low frequency magnetic fields produced by moving magnetic objects like elevators, cars, and trains. BASIC EQUIPMENTOF A MEG DEVICE Shieldedroom www.elekta.com Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 13 The typicalMEG data SEF_signals.jpg BothMEGandEEGrawdataareoftenpresentedastime-dependentsignals,arrangedinatopographicallayout.Thesedatamayeitherrepresentaveragesoverrepeatedsensorystimuliormotorresponsesorcontinuousrawdata.Thelatterareroutinelyemployedintheanalysisofabnormalepilepticactivityorinthecharacterizationofongoingrhythmicactivity. Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 14 SOURCELOCALIZATION INVERSEPROBLEM: Inordertodeterminethelocationoftheactivitywithinthebrain,advancedsignalprocessingtechniquesareusedwhichusethemagneticfieldsmeasuredoutsidetheheadtoestimatethelocationofthatactivity'ssource. TheMEGinverseproblemistheoreticallyill-posed,havingmanysolutionstoasingleproblem.Allsourcelocalizationmethodsmakeassumptionsabouthowthebrainmightwork(e.g:dipolefittingmodel,minimumnormbasedapproaches,seeLecture9,12). Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 15 SOURCELOCALIZATION(CONT.) FORWARDPROBLEM: Itisasituationwhereweknowwhereanysourcesareandweareestimatingthefieldatagivendistancefromthem. OrinotherwordsthisistheproblemofcomputingwhattheoutputoftheMEGsensorswouldbeifacertainregionofcortexwereactive.(e.g:dipolarsourceandvolumeconductormodels). Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 16 THE TEMPORALAND SPATIALRESOLUTIONOF MEG Temporal resolution: – Milliseconds. MEG allows real-time recording of the brain activity. Spatial resolution: – From several millimeters to a couple of centimeters, depending on the experiment. Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 17 WHAT ARE SOME FEATURES/BENEFITS OF MEG? MEG is completely noninvasive and non-hazardous. The data can be collected in the natural seated position allowing more life-like cognitiveexperiments than fMRI. The measurement environment is completely silent, which facilitates especially auditory studies. MEG has an extremely high temporal resolution (milliseconds) and also provides a good spatial resolution. Signals can be recorded over the whole cortex. There is no need to paste electrodes on the scalp as with EEG. Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 18 RESEARCH AND CLINICALAPPLICATIONS In research, MEG'sprimary use is the measurement of time courses of activity, as such time courses cannot be measured usingfunctional magnetic resonance imaging(fMRI). MEG is alsousedtoanalyseaccurately pinpoints sources in primary auditory, somatosensory and motor areas In somecases MEG should preferably be used in combination with fMRI, becausethereis a needtocreatefunctional maps of human cortex during more complex cognitive tasks. The localization of ictaland inter-ictalspike complexes with MEG is now widely used to identify epileptic foci for the surgical treatment of intractable epilepsy. Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 19 REVIEWQUESTIONS 1. Whatis thedefinitionof magnetoencephalography? 2. Whatdoesitmeasure? 3. HowdoestheMEG work? 4. Whatis a SQUID? 5. Howdoesthe data look like? 6. Whatis theinverseprobleminthecaseof MEG? 7. Whatis theforwardproblem? 8. Whataretheclinicalapplicationsof MEG? Electrophysiological Methods For The Study Of The Nervous-And Muscular-systems: Magnetoencephalography www.itk.ppke.hu 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 20 REFERENCES http://web.mit.edu/kitmitmeg/whatis.html http://en.wikipedia.org/wiki/Magnetoencephalography http://www.scholarpedia.org/article/Magnetoencephalography# http://www.neurosurgery.pitt.edu/imageguided/meg/index.html http://www.britannica.com/EBchecked/topic/1471021/magnetoencephalography http://www.nmr.mgh.harvard.edu/martinos/research/technologiesMEG.php http://psychology.wikia.com/wiki/Magnetoencephalography