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外文资料-- Simulation Study of Electrode System Optimization in Electrical Impedance Tomography.PDF

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外文资料-- Simulation Study of Electrode System Optimization in Electrical Impedance Tomography.PDF

CORRESPONDINGAUTHORSHAHONGEMAILSHA_HONG_2000YAHOOCOMSIMULATIONSTUDYOFELECTRODESYSTEMOPTIMIZATIONINELECTRICALIMPEDANCETOMOGRAPHYWANGYAN,RENCHAOSHI,ZHAOSHU,WANGLEI,SHAHONGINSTITUTEOFBIOMEDICALENGINEERINGCHINESEACADEMYOFMEDICALSCIENCESPEKINGUNIONMEDICALCOLLEGETIANJIN,CHINAEMAILSARAHYKY163CMABSTRACTELECTRODELIESINTHEFRONTOFTHEELECTRICALIMPEDANCETOMOGRAPHYEITSYSTEMANDCONTACTSWITHHUMANBODYDIRECTLYITISONEOFTHEMOSTSENSITIVEANDTHEPIVOTALPARTSOFEITSYSTEMTHETYPEANDTHECONFIGURATIONOFELECTRODESYSTEMINFLUENCETHERECONSTRUCTIONIMAGEGREATLY,ESPECIALLYFORTHECENTRALAREAOFBODY,WHERETHEMEASUREMENTSENSITIVITYISVERYLOWASIMULATIONPLATFORMISDEVELOPEDTOOPTIMIZETHEELECTRODESTRUCTUREPARAMETERBASEDONTHECOERCIVEEQUIPOTENTIALNODESMODELFORTHEIMAGINGOBJECTOFTHEDEEPAREAOFBODYTHEINFLUENCESONTHEMEASUREMENTSENSITIVITYANDTHEIMAGERECONSTRUCTIONQUALITYHAVEBEENSTUDIEDUSINGDIFFERENTELECTRODETYPESANDCONFIGURATIONSTHESIMULATIONRESULTSSUGGESTTHATOPTIMALSELECTIONOFELECTRODETYPESANDCONFIGURATIONSCANHELPFULLYINCREASETHEIMAGEQUALITYANDMEASUREMENTSENSITIVITYOFTHEIMAGEESPECIALLYINCENTRALAREASEVERALTYPEANDCONFIGURATIONPARAMETEROFEITELECTRODETHATFITFORCENTRALOBJECTIMAGINGAREALSOPRESENTEDKEYWORDSEIT;ELECTRODESYSTEM;RECONSTRUCTIONQUALITY;MEASUREMENTSENSITIVITY;SIMULATIONEVALUATIONI0BINTRODUCTIONEITISONEOFTHEIMPORTANTRESEARCHTOPICSINTODAY’SBIOMEDICALENGINEERING13EITELECTRODEARRAYISONEOFTHEMOSTSENSITIVEANDTHEPIVOTALPARTSOFEITSYSTEMUSUALLYTENORMOREELECTRODESAREUSEDINEITSYSTEMTHEELECTRODEARRAYLIESINTHEFRONTOFTHEEITSYSTEMANDCONTACTSWITHHUMANBODYDIRECTLYTHESTRUCTUREANDPERFORMANCEOFTHEELECTRODESYSTEMGREATLYINFLUENCETHEORIGINALINFORMATIONEXTRACTION,REALTIMEPROPERTYOFTHESYSTEM,IMAGERESOLVINGPOWER,ANDESPECIALLYTHEINFORMATIONEXTRACTIONFROMCENTRALAREA,WHERETHEEITMEASUREMENTSENSITIVITYISPOORINTHEEARLYOPTIMUMSTUDYOFELECTRODECONFIGURATION,ITISWIDELYACCEPTEDTHATCURRENTEXCITATIONELECTRODESSHOULDBEASLARGEASPOSSIBLEWHILETHEVOLTAGEMEASURINGELECTRODESAREREQUIREDASSMALLASPOSSIBLE4PINGHUA5STUDIEDTHEINFLUENCEOFCONTACTIMPEDANCEBETWEENELECTRODEANDSKIN,ANDSHOWEDTHATTHEBESTEFFECTCANBEOBTAINEDWHENTHETOTALWIDTHOFELECTRODEARRAYISABOUT8090OFTHEIMAGEDAREA’SPERIMETEREJWOO6USEDANNULARCURRENTANDVOLTAGEELECTRODESCOVERING90OFTHESURFACEPATPINHEIRO7REPORTEDTHATTHEOPTIMUMAREAUNDERNEATHTHEELECTRODESIS80OFTHEOVERALLBOUNDARYAREAFORTHEADJACENTPATTERNSAND60FORTHEOPPOSITEONESWANGCHAOETAL89CARRIEDONTHESIMULATIONRESEARCHONTHEINFLUENCEOFELECTRODEWIDTHUSINGTHECOERCIVEEQUIPOTENTIALNODEFINITEELEMENTMETHODFEMMODEL,ANDSHOWEDTHATTHEBESTEFFECTWASOBTAINEDWHENTHEOVERLAYRATEOFELECTRODESIS571ALTHOUGHCONTINUOUSPROGRESSESONTHECHOICEOFELECTRODESTRUCTUREPARAMETERINEITHAVEBEENMADE,THECOMPLETEANDSATISFACTORYRESULTHASNOTBEENSEENSOFARINPRACTICE,THEDESIGNOFEITELECTRODESTRUCTUREANDPARAMETERISSTILLBASEDONEXPERIENCEAMONGEITELECTRODES,THECOMPOUNDELECTRODEHASMORECOMPLEXSTRUCTUREFOURPARAMETERSOFTHECOMPOUNDELECTRODERESTRICTEACHOTHERANDTHEIRINFLUENCEONEITSYSTEMAREMUCHCOMPLEXTHEINFLUENCESOFALLPARAMETERSSHOULDBECONSIDEREDCOMPREHENSIVELYUSINGONLYTHEOVERLAYRATEOFELECTRODESISNOTAGOODWAYTODEALWITHTHECOMPOUNDELECTRODEOPTIMIZINGDESIGNINEITMEASUREMENT,THECENTRALAREA,CORRESPONDINGTODEEPAREAOFBODY,ISOFTENTHEREGIONOFINTERESTBUTTHEMEASUREMENTSENSITIVITYOFTHECENTRALAREAISRELATIVELYLOWERANDTHEIMAGEQUALITYISRELATIVELYPOORHOWTORAISETHEMEASUREMENTSENSITIVITYANDIMPROVETHEIMAGEQUALITYOFTHECENTRALAREAISAKEYPROBLEMINEITMEASUREMENTTHEEXCITATIONPATTERNISALSOANIMPORTFACTORINEITMEASUREMENTADJACENTEXCITATIONHASMOREINDEPENDENTMEASURENUMBEROPPOSITEEXCITATIONPATTERNHASLESSINDEPENDENTMEASURE,BUTTHEFIELDDISTRIBUTIONISMOREREASONABLETHANTHATINADJACENTPATTERNINTHISPAPER,ASIMULATIONSTUDYOFEITELECTRODESTRUCTUREANDPARAMETERDESIGNAIMINGATTHEIMAGINGOBJECTOFCENTRALAREAISPRESENTEDUSINGTHECOERCIVEEQUIPOTENTIALNODEMODELFORCOMPOUNDELECTRODE10,ASIMULATIONPLATFORMISDEVELOPEDTOCARRYOUTTHEOPTIMIZINGDESIGNOFTHEELECTRODESYSTEMBASEDONTHEMODELANDTHEPLATFORM,THEINFLUENCESOFTHEELECTRODENUMBER,TYPE,CONFIGURATION,ANDEXCITATIONPATTERNOFTHEELECTRODESYSTEMONTHEMEASUREMENTSENSITIVITYANDTHEIMAGERECONSTRUCTIONQUALITYHAVEBEENSTUDIEDTHESIMULATIONSTUDYOFEITIMAGINGWITHDIFFERENTDEPTHSOFIMAGINGOBJECTHASBEENMADEWITHEQUIPOTENTIALBACKPROJECTIONALGORITHM9781424447138/10/25002010IEEEII1BMETHODA4BFINITEELEMENTMODELFORCOMPLEXELECTRODESELECTRODEPLATESINROUNDORRECTANGLESHAPEAREUSUALLYUSEDINEITTHEPROJECTIONSOFBOTHELECTRODESONTHETOMOGRAMPLANEAREALINEANDTHELENGTHOFTHELINEEQUALSTOTHEWIDTHOFTHEELECTRODES,CALLEDLINEELECTRODE,ASSHOWNIN1AND2OFFIG1FORTHECOMPOUNDELECTRODEWITHACOMPLEXSTRUCTURE,THEPROJECTIONONTHETOMOGRAMPLANECONSISTSOF3LINES,ASSHOWNIN3AND4OFFIG1THEEXCITATIONELECTRODECONSISTSOFTWOLINES,JINFIG1,ONTHELEFTANDTHERIGHTRESPECTIVELY,ANDTHEMIDDLELINE,CINFIG1,REPRESENTSTHEMEASUREMENTELECTRODETHEREARE4STRUCTUREPARAMETERSFORTHECOMPOUNDELECTRODEFIG1,THEEXCITATIONELECTRODEWIDTHJ,THEMEASUREMENTELECTRODEWIDTHC,THESPACEBETWEENTHEEXCITATIONELECTRODEANDTHEMEASUREMENTELECTRODEB,ANDTHEDISTANCEBETWEENTWOADJACENTCOMPOUNDELECTRODESAEACHOFTHEMISPRESENTEDBYTHECOUNTOFFEMNODESFORANEITELECTRODESYSTEMWITHCERTAINBOUNDARYSUCHAS256NODESINTHISSTUDY,WHENTHEELECTRODENUMBERS32HEREANDELEMENTSDIVIDEDINFEM1210HEREAREDETERMINED,THESUMOFELECTRODEWIDEANDTHESPACEBETWEENADJACENTELECTRODESISFIXEDTOO8HEREFIGURE1THELINEELECTRODEANDCOMPOUNDELECTRODEINEITAFINITEELEMENTMETHODFEMOFTHECOMPOUNDELECTRODEUSINGCOERCIVEEQUIPOTENTIALNODEMODELHASUSEDTOSTUDYTHEEITELECTRODESTRUCTUREPARAMETEROPTIMIZING10B5BESTIMATEFUNCTIONSINORDERTOESTIMATETHEINFLUENCESOFELECTRODESTRUCTUREANDPARAMETERSONTHEMEASUREMENTSENSITIVITYANDTHEIMAGERECONSTRUCTIONQUALITYINEIT,THEMEASUREMENTSENSITIVITYFUNCTIONSANDTHEIMAGERECONSTRUCTIONQUALITYFUNCTIONDAREDEFINEDRESPECTIVELYASFOLLOWS110BTHEMEASUREMENTSENSITIVITYFUNCTIONS10011010∑∑−−NIMJIJSNMSHEREMISTHEMEASUREMENTNUMBERCORRESPONDINGOFONECURRENTEXCITATIONNISTHENUMBEROFCURRENTEXCITATIONSSIJDENOTESTHEMEASUREMENTSENSITIVITYFORJTHMEASUREMENTINITHCURRENTEXCITATION0101ΣΣ−−VVSIJSIJSHOWSTHATTHEVOLTAGEOFTHEMEASUREMENTELECTRODECHANGESFROMV0TOV1WHILETHECONDUCTANCEOFACERTAINREGIONINTHEMEASUREDFIELDCHANGESFROMΣ0TOΣ1SISTHEAVERAGESENSITIVITYOFALLNTIMESOFEXCITATIONSITONLYDEPENDSONTHEELECTRICFIELDDISTRIBUTIONDUETOTHECONDUCTANCECHANGEOFTHEMEASUREDREGION,ANDISINDEPENDENTOFIMAGERECONSTRUCTIONALGORITHMANDHARDWAREERRORSSUPPOSETHATSIGNALTONOISERATIOOFEACHELECTRODEISFIXEDTHEBIGGERTHESIS,THEHIGHERTHEMEASUREMENTSENSITIVITYIS211BTHEIMAGERECONSTRUCTIONQUALITYFUNCTIOND10025511−∑MPSPGPGIMD(P1,2,M)HEREMISTHENUMBEROFALLTHEELEMENTSDIVIDEDINTHEIMAGINGREGIONGSPISTHEGRAYVALUEOFPTHELEMENTINTHEIMAGINGMODELGIPISTHEGRAYVALUEOFPTHELEMENTINTHERECONSTRUCTEDIMAGEDSHOWSTHENORMALIZEDAVERAGEVALUEOFTHEGREYSCALEDIFFERENCESBETWEENTHERECONSTRUCTEDIMAGEANDTHEIMAGINGMODELOFEACHELEMENTINTHEIMAGINGREGIONDSENSITIVELYREFLECTSTHERECONSTRUCTEDIMAGEQUALITYUSINGD,THEDIFFERENCEBETWEENTHERECONSTRUCTEDIMAGEANDTHEIMAGINGMODELCANBEEVALUATEDWITHOUTANYIMAGEPROCESSINGTHESMALLERDIS,THELESSTHEDIFFERENCEBETWEENTHERECONSTRUCTEDIMAGEANDTHEIMAGINGMODELIS,THEHIGHERTHERECONSTRUCTEDIMAGEQUALITYISC6BIMAGINGMODELSINTHESTUDYOFTHISPAPERTHETOTALNUMBEROFFINITEELEMENTSIS1210,INCLUDING734NODESTHEREARE256NODESONTHECIRCUMFERENCEOFTHEMEASUREDFIELD6IMAGINGMODELSCORRESPONDINGTODIFFERENTMEASUREMENTDEPTHHAVEBEENUSEDFIG2THEIMAGEDOBJECTMOVESFROMTHEBOUNDARYTOTHECENTRALAREAFROMMODEL1TO6,ANDTHEMODEL6ISTHEIMAGEDOBJECTOFCENTRALAREA,CORRESPONDINGTODEEPAREAOFBODYIII2BSIMULATIONEXPERIMENTANDRESULTA7BEFFECTSOFELECTRODENUMBEREITSYSTEMWITH8,16,32,64,128AND256POINTELECTRODESAREUSEDRESPECTIVELYFORSTUDYTHEESTIMATERESULTSUSINGFUNCTIONSDFOR6IMAGINGMODELSINFIG1ISSHOWNINFIG3THEIMAGINGRESULTSOFMODEL3ANDMODEL6ARESHOWEDINFIG4BEFFECTSOFELECTRODETYPEANDSTRUCTUREPARAMETERTHERECONSTRUCTIONIMAGESHAVEBEENMADEUSINGTHECOERCIVEEQUIPOTENTIALNODEMETHODFORLINEELECTRODEANDCOMPOUNDELECTRODESOMECOMPARISONSTUDIESOFTHEPARAMETERINFLUENCESONMEASUREMENTSENSITIVITYANDRECONSTRUCTIONQUALITYBETWEENLINEELECTRODEANDCOMPOUNDELECTRODEHAVEBEENCARRIEDOUTFIGURE2IMAGINGMODELSOFDIFFERENTDEPTHSFIGURE3THEEFFECTSOFELECTRODENUMBERONIMAGEQUALITYFIGURE4IMAGINGRESULTSWITHDIFFERENTELECTRODENUMBERFORMODEL3AND6THETOTALWIDTHOFBOTHLINEELECTRODEANDCOMPOUNDELECTRODEARESETTOTHESAMEASANEXAMPLE,THEWIDTHOFLINEELECTRODEIS5FEMNODES,WHILECOMPOUNDELECTRODEHAS3CASES,INWHICHTHETOTALWIDTHSOFTHEMAREALSO5FEMNODESTHEFIRSTA3,J1,C3ANDB0,THESECONDA3,J1,C1ANDB1,THETHIRDA3,J2,C1ANDB0THEOTHERCASESOFDIFFERENTWIDTHHAVESIMILARRESULTTHEFUNCTIONSSANDDOFTHERECONSTRUCTIONIMAGESCORRESPONDINGTOIMAGEMODEL6ANDMODEL3RESPECTIVELYHAVEBEENCALCULATEDANDSHOWNINTABLEIANDTABLEIIC9BEFFECTOFEXCITATIONPATTERNTHEEFFECTOFEXCITATIONPATTERNOFEITONTHERECONSTRUCTEDQUALITYANDTHEMEASUREMENTSENSITIVITYHASINVESTIGATEDTHEEXCITATIONPATTERN,WHICHDETERMINESHOWTHECURRENTFLOWSINTOTHEINTERESTINGAREA,INFLUENCESTHEDISTRIBUTIONOFELECTROMAGNETICFIELDDIRECTLYINTHISSTUDY,THEADJACENT,INTERVALANDOPPOSITEEXCITATIONMODEAREUSEDTAKEN32ELECTRODESASANEXAMPLE,THEEXCITATIONCURRENTISAPPLIEDBYTWOELECTRODES,ANDTHEINTERVALOFTHEELECTRODESISCHANGEDFROM1TO16WHENTHEINTERVALIS1,ITISADJACENTEXCITATIONANDWHENTHEINTERVALIS16,ITISOPPOSITEEXCITATIONOTHERCASESARECALLEDINTERVALEXCITATION,FIG5THERECONSTRUCTIONRESULTSOF32ELECTRODESATINTERVALSOF1,4,8,12,16ELECTRODESRESPECTIVELYHAVEBEENMADEWITHTHEIMAGEMODELSSHOWNINFIG2THEEFFECTSOFEXCITATIONPATTERNONIMAGEQUALITYANDMEASUREMENTSENSITIVITYHAVEBEENSHOWNINFIG6ANDFIG7TABLEICOMPARISONOFLINEELECTRODEANDCOMPOUNDELECTRODEFORMODEL6TABLEIICOMPARISONOFLINEELECTRODEANDCOMPOUNDELECTRODEFORMODEL3FIGURE5ADJACENTEXCITATION,INTERVALEXCITATIONANDOPPOSITEEXCITATIONPATTERNFIGURE6EFFECTSOFEXCITATIONPATTERNONIMAGEQUALITYELECTRODETYPEANDSTRUCTUREPARAMETERDSLINEELECTRODE5NODESWIDE187060003979A3J1C3B0185840003897A3J1C1B1185760003889A3J2C1B0185890003977ELECTRODETYPEANDSTRUCTUREPARAMETERDSLINEELECTRODE5NODESWIDE143560001871A3J1C3B0146100001836A3J1C1B1144750001831A3J2C1B0144510001875510152025308163264128256DELECTRODECOUNTMODEL6MODEL5MODEL4MODEL3MODEL2MODEL100005001001500200251481216SINTERVALOFCURRENTELECTRODESMODEL6MODEL5MODEL4MODEL3MODEL2MODEL1FIGURE7EFFECTSOFEXCITATIONPATTERNONMEASUREMENTSENSITIVITYIV3BRESULTSANDDISCUSSIONSFROMFIG3ANDFIG4,ITISSHOWEDTHATFORNONCENTRALIMAGINGOBJEC

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