Diffusion tensor imaging and the measurement of diffusion tensors in biological systems PDF
Preview Diffusion tensor imaging and the measurement of diffusion tensors in biological systems
DIFFUSIONTENSORIMAGINGANDTHEMEASUREMENTOFDIFFUSION TENSORSIN BIOLOGICALSYSTEMS By LEIYANG ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1999 Copyright1999 By LeiYang ACKNOWLEDGEMENTS Iwouldliketothankmysupervisor,Dr.Andrew,forhiskindness,patience,and encouragementofmygraduatecareer.Withouthim,thisdissertationwouldnothave beenfinished.Ilearnedmuchfromhisdeepinsightsinto Physics.Iwouldalsoliketo thankmyresearchsupervisor,Dr.Mareci,forhisgenerosityandguidance.Heledmeand thewholeresearchgroupintothediffusionimagingarea,whichhasproducedonepaper, twoSMRMconferenceoralpresentations,threeconferenceabstracts,andthreemore submittedpapers.Hisexcellentideaofintroducingcoherencetransferpathwayintothe diffusion-weightingcalculationwasthestartingpointofthenewformulaandnew diffusiontensorimagingmethods.AlsothankstoDr.Inglisforteachingmeeverydetail aboutNMR,givingmeinvaluablesuggestionsaboutmyresearch.Iwouldalsoliketo givespecialthankstoDr.SullivanandtoDr.Yeltonfortakingcareofinternational studentslikemewhowasthousandsofmilesawayfromhomeandstrugglingtosurvive inaforeigncountry. Iexpressmysincerethankstomanycolleagueswhohavemademystayatthe UniversityofFloridasomethingthatIwillrememberfondlyforyears.IappreciateDr. Wirth,Dr.Jones,Dr.Harris,XeveSilverfortheirhelpinsurgery,Dr.Briggsforletting meusehisoffice,Dr.Fitzsimmonsforhelpingmebuildtherfcoil,DanPlantfor hardwaresupport,andHaiquanDaiforcomputersupport. iii Thisthesisisdedicatedtomyfather,YuhuiYang,whosurvivedthedisasterof theculturalrevolutionsince1967.Itwashistoleranceandlovethatsupportedmeandmy wholefamilythroughthedarkages. AlltheseachievementbelongtoJesusChrist,mylordandsavior.Heisalways withme,nomatterwhathappens.MayallpraisesgotoGod! iv TABLEOFCONTENTS Page ACKNOWLEDGMENTS i« ABSTRACT ix CHAPTERS 1 INTRODUCTIONANDBACKGROUND 1 Introduction 1 Background 4 BrownianMotionandDiffusionDistance 4 DiffusionEffectsonNMR 5 MethodsforApparentDiffusionCoefficient(ADC)Measurement 6 Bipolargradientpulsespin-echosequence 6 Bipolargradientpulsestimulated-echosequence 7 Problemsforthesetwotechniques 7 DiffusionCoefficientasanImportantParameterinBiomedicalSystems 8 ClinicalapplicationofdiffusionMRimaging 9 UnsolvedProblem:b-ValueCalculationforAnyOrderofQuantumCoherence....9 b-Valuecalculationproblemindifferentsequence 9 b-Valuecalculationprobleminmultiplequantumcoherence 11 Conclusion 11 2 ACOHERENCETRANSFERAPPROACHTOGRADIENT WEIGHTINGFACTORCALCULATION 17 Theory 17 SpinEvolutioninthePresenceofAnisotropicDiffusion 18 ExplicitEffectofRFPulses 21 ApplicationtoDifferentPulseSequences 23 ApplyingtheTheorytoSingleQuantumCoherenceSequences inIsotropicCondition 24 Gradientechosequence 24 Spin-echosequence 24 Stimulcated-echosequence 25 DoubleQuantumCoherence 25 3 DIFFUSIONTENSORMETHODS 28 v DataAcquisitionandProcessing 28 FormulasforDataAcquisition 28 DataProcessing 30 SpinEchoandStimulatedEchoDiffusionTensorImaging 30 b-MatrixofSpinEchoSequence 30 b-MatrixofStimulatedEcho 32 Experiments 34 Conclusion 36 4 FASTDIFFUSIONTENSORIMAGINGUSINGAMULTIPLE STIMULATEDECHOSEQUENCE 41 Introduction 41 Methods 41 b-MatrixCalculationforStimulatedEchoSequence 41 GeneralLibraryforb-MatrixCalculationforStimulatedEcho 43 MultipleStimulatedEchoSequence 44 Results 46 WaterandCeleryExperiments 46 RatBraininvivoExperiments 51 5 HIGH-RESOLUTIONDIFFUSIONTENSORANDCOLORED TRACEIMAGINGOFRATSPINALCORDINVITRO 53 Introduction 53 DiffusionTensorImaging 53 AnisotropyIndex 54 AnatomicStructureofSpinalCord 55 Graymatterofspinalcord 55 Whitematterofspinalcord 56 Methods 56 FixationofRatSpinalCord 56 DiffusionTensorImagingExperiments 56 DataAnalysis 58 Results 58 DiffusionTensorValuesofNormalSpinalCord 58 DiffusionTensorValuesofInjuredSpinalCord 59 ColorsinGrayMatterRegion 59 ColorTraceImages 59 ColorsinGrayMatterRegionofNormalRatSpinalCord 59 ColorsinWhiteMatterRegionofNormalRatSpinalCord 60 ColorTraceImagesofInjuredSpinalCord 60 TraceisanImportantParameterforDifferentNerveTissues 60 AnisotropyIndexofNormalRatSpinalCord 60 vi AnisotropyIndexofNormalandInjuredWhiteMatterTissues 61 DiffusionTensorImagingofHumanSpinalCord 61 Conclusion 61 6 HIGH-RESOLUTIONDIFFUSIONTENSORANDCOLORED TRACEIMAGINGOFNORMAL,HYDROCEPHALUSANDSHUNTEDRAT BRAININVITRO 75 Introduction 75 InfantileHydrocephalus 75 ShuntTreatmentofHydrocephalus 76 WhiteMatterPathologyinHydrocephalus 76 MRImagingTechniques 77 AnatomyStructureofRatBrain 78 Methods 78 FixationoftheRatBrain 78 ShuntSurgery 78 Microimaging 78 DataProcessing 80 Results 81 DiffusionTensorValuesofNormalRatBrain 81 DiffusionTensorValuesofHydrocephalusRatBrain 81 DiffusionTensorValuesofRatBrain 81 ColorTraceImages 81 ColorinCerebralCortex 81 ColorinCorpusCallosum 82 AnisotropyIndexofWhiteMatterinNormalandHydrocephalicRatBrain 82 DiffusionTensorTraceofLateralandDorsalCortex 82 StimulatedEchoDiffusionTensorImaging 83 Conclusion 83 7 SUMMARY,INTERPRETATION,ANDCONCLUSION 98 Introduction 98 AchievementsandSignification 98 ANewFormulaforEvaluatingDiffusionWeighting 98 TwoDiffusionTensorImagingTechniques 99 DiffusionTensorImagingofNormalandInjuredSpinalCord 99 DiffusionTensorImagingofNormal,HydrocephalusandShuntedRat Brain 100 DiffusionModelinMolecularLevel 100 FutureStudies 107 DoubleQuantumDiffusionTensorImagingandSpectroscopy 107 SpinalCordInjuryModel 107 InVivoDiffusionTensorImaging 107 Summary 107 vii REFERENCE 109 BIOGRAPHICALSKETCH 113 viii AbstractofDissertationPresentedtotheGraduateSchooloftheUniversityofFlorida inPartialFulfillmentoftheRequirementsforthe DegreeofDoctorofPhilosophy DIFFUSIONTENSORIMAGINGANDTHEMEASUREMENTOFDIFFUSION TENSORSIN BIOLOGICALSYSTEMS By LeiYang May1999 Chairman:E.RaymondAndrew MajorDepartment:Physics Thisdissertationrevisitsthetheoryofdiffusion-weightingfactorof gradientsforanysequenceandpresentsanewcomprehensiveformulawhichnotonly unifiesallformerresults,butalsopredictsnewresultsforunsolvedpulsesequences. Then,onthebasisofthisnewformula,twodiffusiontensorimagingtechniqueswere built,tested,andappliedtotheratspinalcordandbrain,thusshowingthebiologicaland clinicalsignificanceofdiffusiontensorimaging. Therehavebeenmanypreviousattemptstoderiveanexpressionofdiffusion- weightingfactorofgradientsindifferentpulsesequences,butuntilnow,nobodyhas beenabletoderiveaformulaforanydouble-quantumandmultiple-quantumcoherence sequences,onlyunderincasehadthisproblembeensolvedexperimentally.This dissertationintroducesanewmethodwhichnotonlyunifiesalldifferentexpressionsfor singlequantumcoherence,butalsopredictstheexpressionsfordouble-quantumand ix multiple-quantumcoherencesequences.Next,usingthenewformulafordiffusion- weightingfactor,twodiffusiontensorimagingtechniqueswerebuilt:spinechodiffusion tensorimagingandmulti-stimulatedechodiffusiontensorimaging.TheEcho-Plan Imaging(EPI)spinechodiffusiontensorimaginghadbeenbuiltin1994, butthemulti- echostimulatedechodiffusiontensorimagingtechnique,alongwithBasser's EPI stimulatedechodiffusiontensorimagingtechnique,werethefirsttwotechniquesinthe worldthatusedstimulatedechosequenceindiffusiontensorimaging. Inthisdissertation,diffusiontensorimagingtechniqueswerefirstappliedto normalandinjuredratspinalcordsandbrain,colortraceimageswerepresentedwhich clearlyshowthefiberorientationsofthespinalcordthatwerenotaccomplishedbyany otherMRI. Wefoundthattheinjuryofthespinalcordcausesthelossofanisotropyof whitematter,whichisconsistentwithotherresultsusingapparentdiffusioncoefficient (ADC).Itisinterestingthatthereweresubstantialchangesindiffusioncharacteristicsin theinjuredareawhichappearednormalbyconventionalimaging. Theseresultsimply thatthereareconsequencesofspinalcordinjurywhichdramaticallyalteraxonstructure butdonotchangewatercontent,soarenotdetectedbyconventionalimaging.Wefound thatthehydrocephalusoftheratbraincausesthelossofanisotropyofwhitematter,and hydrocephalusresultsinincreasedwatercontentinthebrainsurroundingtheventricles. Thishasbeenconfirmedbyindependentmeasurements. Thisisanewdirectioninthenoninvasiveinvestigationofthenormaland abnormalbrainandspinalcordusinganewimagingtechniquetostudytissue organization,pathologicalchanges,andrecoverywithtreatment.Thetechniquecould ultimatelybeappliedtoclinicalsituations(inthesamewayasADCisnowbeingapplied X
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