345
ReviewArticle
Areviewofdiffusiontensorimagingstudiesonmotorrecoverymechanismsinstrokepatients
S.H.Jang
DepartmentofPhysicalMedicineandRehabilitation,CollegeofMedicine,YeungnamUniversity,317-1,Daemyungdong,Namku,Taegu,705-717,RepublicofKorea
Tel.:+82536203269;Fax:+82536203269;E-mail:strokerehab@hanmail.net,belado@med.yu.ac.kr
Abstract.Forthepastdecade,diffusiontensorimaging(DTI)hasbeenusedinelucidationofthemotorrecoverymechanismsinstrokepatients.Inthecurrentstudy,IreviewedtheDTIstudieswithregardtothemotorrecoverymechanismsinstrokepatients,accordingtothefollowingclassificationofmotorrecoverymechanisms;recoveryofadamagedlateralcorticospinaltract(CST),subcorticalperi-lesionalreorganization,ipsilateralmotorpathwayfromtheunaffectedmotorcortextotheaffectedextremities,andothermotorrecoverymechanisms.Inaddition,IdiscussedthecharacteristicsofDTIasanevaluationtoolformotorrecoverymechanismsandfuturedirection.DTIhasauniqueadvantageinidentificationandestimationofneuraltractsatthesubcorticallevel.Therefore,itcouldcontributemuchtoresearchonthemotorrecoverymechanismsofstrokepatients,especially,intermsofrecoveryofadamagedCSTandsubcorticalperi-lesionalreorganization.InspiteoftheadvantagesofDTI,fewerDTIstudiesonthistopichavebeenconductedcomparedtostudiesusingtranscranialmagneticstimulationorfunctionalMRI.Therefore,thetotalnumberofDTIstudiesonthistopicshouldbeincreased.Moreover,furtherstudiesonvarioustopicsrelatedtobrainplasticityofmotorfunction,aswellasthemotorrecoverymechanismitself,shouldbeencouraged;forexample,DTIchangeswithpassageoftime,withrehabilitativeintervention,orwithmotorrecovery.
Keywords:Stroke,diffusiontensorimaging,diffusiontensortractography,hemiparesis,motorrecovery,brainplasticity
1.Introduction
Becausemotorweaknessisoneofthemostseri-ousdisablingsequelaeofstroke,manystudieshaveat-temptedtoelucidatethemotorrecoverymechanismsofstroke[5,7,10,11,13,18,22,26–28,60,61,71].Beforethedevelopmentofdiffusiontensorimaging(DTI),transcranialmagneticstimulation(TMS)andfunction-alneuroimagingweremainlyusedforresearchonthemotorrecoverymechanismsofstroke.Consequently,severalmotorrecoverymechanismshavebeensuggest-ed:theipsilateralmotorpathwayfromtheunaffectedmotorcortextotheaffectedextremities,peri-lesionalreorganization,recoveryofadamagedlateralcorti-cospinaltract(CST),andcontributionofthesecondarymotorarea[5,7,10,11,13,22,26–28,60,61,71].DTIhasauniqueadvantageinidentificationandes-timationofneuraltractsatthesubcorticallevel[2,3,47,49].Forthepastdecade,sincethedevelopmentofDTI,DTIhasmadeagreatcontributiontoresearchinneuroscience.Ithasalsocontributedmoretoresearchonthemotorrecoverymechanismsofstrokeinthefol-lowingaspectsthanpreviousTMSandfunctionalMRI(fMRI)studies;1)recoveryofadamagedlateralCST(accuratelocalizationofaCSTlesionandrecoveryoftheCSTlesion),2)peri-lesionalreorganizationatthesubcorticallevel(pathwaychangeofaneuraltract),and3)contributionofotherneuraltractsorstructuresascompensationforneuraltractdamage.
Inthecurrentstudy,IreviewedDTIstudieswithre-gardtothemotorrecoverymechanismsinstrokepa-tients,accordingtothefollowingclassificationofmo-
ISSN1053-8135/11/$27.502011–IOSPressandtheauthors.Allrightsreserved
346S.H.Jang/AreviewofdiffusiontensorimagingstudiesonmotorrecoverymechanismsTable1
Previousdiffusiontensorimagingstudiesonmotorrecoverymechanismsinstrokepatients
Authors
Publicationyear
RecoveryofadamagedCSTJangetal.2006Jangetal.Yangetal.Panneketal.Schaechteretal.
2007200820092009
Noofpatients1111010123114053
Etiology
LocationoflesionCR,ICCR,BGCRCorticalSubcortical
TimingofDTIafteronset3weeks,5months1,4,16months2weeks,10months10∼382days6months<6months6months11∼19weeks6months7years10months6∼92days7∼28days20∼30months6months3∼94months
DTIParameters
Othercombinedevaluation
HemorrhageHemorrhageHemorrhageInfarctInfarctInfarctInfarctInfarctInfarctHemorrhageInfarctHemorrhageInfarctInfarctHemorrhage
FAADC
IntegrityonDTTChangesofDTTIntegrityonDTTConnectivityonDTT
TMS,fMRITMS
Peri-lesionalreorganizationJangetal.2006Ahnetal.2006Kwonetal.2007Jangetal.
2009
CR
PonsCRCRCortexCRCRCR,BGCR,ICPonsCR,BG
PathwayonDTTPathwayonDTTPathwayonDTTPathwayonDTTPathwayonDTT
TranscallosalfiberonDTT
FA.ADC.fibernumber
CorticofugalfibersonDTT
PathwayonDTT
TranspontinefiberonDTT
fMRIfMRITMS,fMRIfMRI
IpsilateralmotorpathwayJangetal.2005Jangetal.2009Kwaketal.
2010
OthermotorrecoverymechanismsNewtonetal.20063JangYeoetal.
20092010
142
fMRIfMRI
DTI:diffusiontensorimaging,CST:corticospinaltract,CR:coronaradiata,IC:internalcapsule,FA:fractionalanisotropy,ADC:apparentdiffusioncoefficient,DTT:diffusiontensortracotgraphy,BG:basalganglia,TMS:transcranialmagneticstimulation,fMRI:functionalmagneticresonanceimaging.
torrecoverymechanisms;recoveryofadamagedlat-eralCST,subcorticalperi-lesionalreorganization,ipsi-lateralmotorpathway,andothermotorrecoverymech-anisms.Relevantstudieswereidentifiedusingthefol-lowingelectronicdatabases(PubmedandMEDLINE)from1966to2010.Thefollowingkeywordswereused:stroke,brainplasticity,rehabilitation,motorre-covery,functionalrecovery,hemiparesis,brainmap-ping,fMRI,TMS,DTI,anddiffusiontensortractog-raphy(DTT).Ilimitedthisreviewtoinjurydependentrecoverymechanismsofhumanadultstroke,and,fi-nally,13studieswereselectedforthisreview[1,24,25,29,31,34–36,40,41,51,54,58,77,78].
2.CharacteristicsofDTIasanevaluationtoolformotorrecoverymechanismsinstrokepatientsDTIallowsevaluationofwhitemattertractsbyvirtueoftheirabilitytovisualizewaterdiffusioncharacteris-tics[3,47].Innormalwhitematter,watermoleculesmoverelativelyfreelyinadirectionparalleltonervefibertracts;theirmovements,however,arerestrictedacrossthetracts,causingdiffusionanisotropyofthewhitematter[3,47].Diffusionanisotropyhasbeenusedinevaluationoftheextentoffiberdamageorre-coveryindiseasesthataffectwhitematter[2,31,49,59,63].Fractionalanisotropy(FA)isthemostwidelyusedparameterofDTI[2,49].TheFAvaluerepresentsthedegreeofdirectionalityofmicrostructures,suchasaxons,myelin,andmicrotubules,andhasarangeofzero(completelyisotropicdiffusion)toone(complete-lyanisotropicdiffusion).TheFAvaluewillincreasewithincreasedorganizationofwhitemattertracts;incontrast,adecreaseintheconditionisrelatedtodisin-tegrationofaneuraltract[2,49].Theapparentdiffu-sioncoefficient(ADC)valueindicatesthemagnitudeofwaterdiffusion[2,49].Itcanbeincreasedwithsomeformsofpathology,particularlyvasogenicedemaoraccumulationofcellulardebrisfromaxonaldamage[2,49].Besides,thefibernumberofaneuraltractandtheintegritychangeofDTThavebeenusedasDTIpa-rameters[59,63,64,66].Thevalidityoftheseparame-tershasbeenestablished[2,31,40,49,59,63,64,66,77].
S.H.Jang/Areviewofdiffusiontensorimagingstudiesonmotorrecoverymechanisms347
Consequently,DTIenablesustonumericallyestimatethestateorchangeofaneuraltractandcanprovidethefollowinguniqueadvantagesforresearchonmotorrecoverymechanismsinstrokepatients.First,evalua-tionofthegeneralstate,lesionsite,injuryseverityofalesion,orchangesinlesions(regenerationordegenera-tion)ofneuraltracts;second,estimationofchangesinotherneuralstructuresorneuraltractsfollowingstroke.Moreover,ithasrecentlybeenusedinevaluationofchangesofthenucleusinthehumanbrain[17,44].Onthecontrary,DTIhasseverallimitationsthatmustbeovercomeinordertoachieveamoreaccurateesti-mationofaneuraltract.Thefibertrackingtechniqueisoperator-dependent,andcannotbeusedindiscernmentofthesomatotopyatthecortexlevel.Besides,theprob-lemassociatedwithkissingfiber,limitationindepictionofacrossingfiber,andlowsensitivitycomparedwithTMSshouldberesolved[30,43,55,72].Manystudieshaverecentlyattemptedtosolvetheseproblemsusingprobabilistictractographyorcombinedstudywithoth-erbrainmappingtechniques(fMRIorTMS)[1,25,26,55,72].
2.1.RecoveryofadamagedlateralCST
TheCSTisthemostimportantneuraltractformotorfunctioninthehumanbrain.Therefore,preservationorrecoveryoftheCSTismandatoryforgoodrecoveryofimpairedmotorfunctioninstrokepatients[4,65,70].ManyTMSandfMRIstudieshavedemonstratedthisrecoverymechanismindirectlybythefindingoftheincrementofactivationintheaffectedprimarysenso-rimotorcortex(SM1)orincreaseoftheamplitudeofmotorevokedpotential(MEP)obtainedintheaffectedsideaccordingtoconcurrentmotorrecovery[6,11,21,33,46,68].
SeveralDTIstudieshavereportedonthisrecov-erymechanisminstrokepatients[31,34,54,58,77].In2006,apatientwithanintracerebralhemorrhage(ICH)wasreportedtoshowrecoveryofapartiallydamagedCSTintermsofchangesinDTIparametersandDTTonthelesion[31].Thepatientshowedcompleteparal-ysisoftheleftextremitiesfollowingICHintherightcoronaradiata(CR)andinternalcapsule.Weaknessoftheaffectedextremitiesslowlyrecoveredtothenor-malrangefor5monthsfromonset.DecreasedFAandincreasedADCvaluesinICHlesionsonthe3-weekDTIwerenormalizedasmuchasthoseofnor-malcontrolsonthe5-monthDTI.Inaddition,thein-tegrityoftheCSTonDTTshowedimprovementonthe5-monthDTTcomparedwiththatofthe3-week
DTT.Subsequently,in2007,therecoveryprocessforadamagedCSTinapatientwithICHintheleftCRandbasalgangliawasdemonstratedusingacombinedstudyofDTT,TMS,andfMRI[34].Thepatientpre-sentedwithcompleteparalysisoftherightextremitiesattheICHonset.Overthe16monthperiodfollowingonset,motorfunctionoftheaffectedextremitiesslowlyrecoveredtoanearlynormalstate.DTTshowedthattheoriginoftheCSThadchangedfromtheposteriorparietalcortex(1month),primarysomatosensorycor-tex(4months),andprimarymotorcortex(16months).TMSandfMRIprovidedadditionalevidencebyrecov-eryofthedamagedlateralCST.RecoveryoftheoriginofthedamagedCSTbytheprocessofnormalizationfromtheparietalcortextotheprimarymotorcortexwassuggestedasoneofthevariousmotorrecoverymechanismsofICH.In2008,Yangetal.reportedonapatientwithICHintheleftCRwhoshowedrecov-eryofaseverelydamagedCSTusingfollowupDTTandTMS[77].TheCSToftheaffectedhemispherewasdisruptedattheCRlevelbytheICHon2-weekDTT;however,thedisruptionoftheaffectedCSTwasrecoveredon10-monthDTT.AnMEPwhichhadthecharacteristicsoftheCSTwasevokedattheaffectedhandonthe10-month,althoughnoMEPwasevokedonthe2-weekTMSstudy.In2009,Panneketal.demon-stratedthatdynamiccorticospinalwhitematterconnec-tivitychangesduringstrokerecoveryusingfollowupprobabilistictractographyin10patientswithcerebralinfarct[54].TheyfoundthattheconnectivityoftheCSTwithintheaffectedhemispherewasenhancedovertimeandthattheenhancedconnectivitywascorrelatedwithstrokerecovery.Recently,Schaechteretal.re-portedthatmotorskillsignificantlyandpositivelycor-relatedwithFAoftheaffectedandunaffectedCSTin10patientswithcerebralinfarct[58].TheysuggestedthatthelevelofmotorskillrecoverywasrelatedtothemicrostructuralstatusoftheCSTinbothhemispheres.2.2.Subcorticalperi-lesionalreorganizationBeforetheintroductionofDTI,onlyafewstudieswereconductedonpatientsshowingsubcorticallesionsbecausefMRIorTMScouldnotvisualizethemotortractatthesubcorticallevel[56].SeveralDTIstudieshavereportedonsubcorticalperi-lesionalreorganiza-tioninstrokepatients[1,25,29,41].
Threestudieshavereportedonperi-lesionalreorga-nizationattheCRlevel[25,29,41].In2006,apatientwasreportedtohavemotorfunctionoftheaffectedhandthatappearedtobereorganizedintheposterior
348S.H.Jang/Areviewofdiffusiontensorimagingstudiesonmotorrecoverymechanisms
portionoftheinfarctedCR[29].Thepatientshowedcompleteweaknessoftheaffectedupperextremityandtheweaknessrecoveredslowlyfor6monthstoapointofnearlynormalfunction[29].ThecontralateralSM1wasactivatedduringeitheraffectedorunaffectedhandmovementson6-monthfMRI.The6-monthDTTfortheaffectedCSTdescendedalongtheposteriorportionoftheinfarctedCR.Subsequently,Kwonetal.(2007)reportedonthreepatientswhosemotorfunctionoftheaffectedupperextremityseemedtobereorganizedintheposteriorportionoftheinfarctedCRusingfollowupDTT[41].Motorfunctionoftheaffectedupperex-tremityinallpatientsshowedsevereweaknessatonsetandrecoveredtofunctionalstateat6monthsfromon-set.TheaffectedCSTpassedalongtheposteriorpor-tionoftheCRinfarctonboththefirst(11–19weeks)andsecondDTT(6months).Recently,apatientwasreportedtohavelegmotorfunctionthatseemedtobereorganizedintheregionofthewallofthelateralven-tricle[25].Thepatientpresentedwithcompleteparal-ysisoftherightextremitiesattheonsetoftheinfarctintheleftmiddlecerebralarteryterritory,andrecov-eredslowly,tothepointofbeingabletoextendtheaffectedkneeagainstresistanceby9monthswithoutrecoveryoftheaffectedhand.TheaffectedCSTde-scendedthroughthemedialCRatoraroundthewallofthelateralventricleon7-yearDTT.The7-yearTMSandfMRIformotorfunctionoftheaffectedlegshowedresultscompatiblewiththoseforthelateralCST.Find-ingsfromthisstudyindicatedtheimportanceofthesubventricularzone,whichisknowntohavepotentialforneurogenesis,eveninthematurebrain[53].
Asforperi-lesionalreorganizationatlevelsotherthanCR,twopatientswithpontineinfarcthavebeenre-ported[1].In2006,usingDTTandfMRI,Ahnetal.re-portedontwopatientswhoshowedcompleteweaknessatstrokeonsetanddemonstratedperi-lesionalreorga-nization[1].Six-monthfMRIdatarevealedactivationonlyinthecontralateralSM1duringeitheraffectedorunaffectedhandmovements.Six-monthDTIrevealedthattheaffectedCSTpassedalongperi-infarctareas(1patient:lateral,1patient:posterior)inthepons.2.3.Theipsilateralmotorpathway
Theipsilateralmotorpathwayisanormalmotorcontrolpathwayandhasbeenacceptedasoneoftherecoverymechanismsofstroke[8,12,27,38].Amongthemotorrecoverymechanismsofstroke,theipsilat-eralmotorpathwayfromtheunaffectedmotorcortextotheaffectedextremitieshasbeenthemostactively
researched[27].Itisimportantbecauseitisrelatedtopoormotoroutcomeandcanbechangedwithtimeormanipulatedbyvariousrehabilitativeinterventions[8,9,11,14,20,32,33,39,42,46,50,62,67,68].
SeveralDTIstudieshavereportedonthismecha-nism[35,36,40].In2005,astudyusingfMRIandDTTdemonstratedthatapatientwithICHwasabletowalkusingonlytheipsilateralmotorpathwayfromtheun-affectedmotorcortextotheaffectedleg[36].Motorfunctionoftheaffectedlegrecoveredslowlytotheex-tentthatthepatientwasabletoovercomegravityfor10monthsafterICHonset,althoughtheaffectedhandshowednosignificantmotorrecovery.fMRIresultsshowedonlyunaffectedSM1activationduringeitheraffectedorunaffectedkneemovements,andDTTre-vealedthattheCSTwasfoundonlyintheunaffectedhemisphere,butnotintheaffectedhemisphere.
Themechanismthatactivatestheunaffectedmotorpathwayafterstrokeonsethasnotbeenclearlyeluci-dated.However,themostplausibleproposedmecha-nismisbasedonthedisinhibitionhypothesis[19,45,50].Normalmotorcorticesofbothhemispheresmain-tainbalancethroughtranscallosalinhibition.However,whenastrokeoccurs,interhemispherictranscallosalin-hibitionisdecreasedfromtheaffectedside,andmovestowardtheunaffectedside.Asaresult,theunaffectedmotorcortexisrecruitedasthepopulationofpotential-lyavailableneuronsincreases.UsingDTT,Jangetal.demonstratedtheclinicalsignificanceoftranscallosalfibersoriginatingfromtheCSTinpatientswithCRin-farctlocatedbelowthecorpuscallosum[35].Transcal-losalfibersoriginatingfromtheCSToftheunaffect-edhemisphereanddescendingtowardthelesionafterpassingthroughthecorpuscallosumweremorepreva-lentinpatientswithCRinfarctcomparedwithnormalcontrols,andthesepatientsshowedpoorermotorfunc-tion.Therefore,thetranscallosalfibersappearedtocompensateformotorweaknessandweresuggestedasevidenceinsupportofthemechanismoftheipsilateralmotorpathway.Recently,Kwaketal.reportedonCSTchangesintheunaffectedhemisphereattheearlystage(7–28daysafteronset)ofICHusingDTT[69].ThefibernumberoftheCSTintheunaffectedhemisphereofthepatientgroupwasincreasedonDTT;therefore,theysuggestedthatthisphenomenonseemedtobeas-sociatedwithcompensationforCSTdamageintheaf-fectedhemisphere.
3.Othermotorrecoverymechanisms
Exceptfortheabovethreemotorrecoverymecha-nisms,threeDTIstudieshavereportedonotherrecov-
S.H.Jang/Areviewofdiffusiontensorimagingstudiesonmotorrecoverymechanisms349
erymechanisms[24,51,78].Contributionofthesec-ondarymotorarea(premotorcortex[PMC]andsup-plementarymotorarea[SMA])isawell-knownmo-torrecoverymechanismofstroke[13,22,26].In2006,Newtonetal.demonstrateddamagetocorticofugalfibersfromtheSMA,ventralPMC,anddorsalPMCus-ingprobabilisitictractographyinthreechronicpatientswithcerebralinfarct[51].OnfMRIactivationfindingsbyhandmovements,theyfoundactivationchangesbe-tweenthesesecondarymotorareasaccordingtothedamagetocorticofugalfibers;therefore,theysuggest-edthatfunctionalreorganizationcouldoccurbetweensecondarymotorareasaccordingtodamagetocorti-cofugalfibers.
Thepyramidaltractisknowntohaveseveralcollat-eralpathwaysinthehumanbrain[48,52].Theaber-rantpyramidaltractreferstothecollateralpathwayofthepyramidaltractthroughthemediallemniscusinthebrainstem,whichseparatesfromtheoriginalpyrami-daltractatthelevelofthemidbrainandthepons,anddescendsthroughthemediallemniscus[15,73,76].Ithasbeendemonstratedbypathologic,electrophysio-logic,andradiologicstudies[23,57,69,74–76].Are-centDTTstudyreportedononepatientwithapontineinfarctwhoappearedtorecoverthroughtheaberrantpyramidaltractinthebrainstemviaabypassthroughthemediallemniscusfrommidbraintomedullainsteadofinfractedCST[24].Thepatientpresentedwithse-vereparalysisoftheaffectedextremities;however,mo-torfunctionoftheaffectedextremitiesrecoveredslow-lytotheextentthatshewasabletoperformallfinemotoractivities,aswellastowalkwithanormalgaitat6monthsfromonset.ThecontralateralSM1wasac-tivatedduringeitheraffectedorunaffectedhandmove-mentson6-monthfMRI.Six-monthDTTshowedthattheaffectedCSTdescendedalongthemediallemnis-cusfromthemidbraintothepons,andthenrejoinedthepyramidaltractattheuppermedulla.
In2010,Yeoetal.reportedthattranspontineconnec-tionfibers,whichareaconnectionoffibersbetweenCSTsatthepons,originatingfromtheaffectedCSToftheaffectedhemisphere,weremoreprevalentinpa-tientswithICHthaninnormalcontrols[78].Inaddi-tion,theseverityoftranspontineconnectionfiberswascloselyrelatedtomotorweaknessinaffectedextremi-tiesandtotheextentofCSTinjuryintheaffectedhemi-sphere.Therefore,theysuggestedthatthetranspontineconnectionfibersappearedtorepresentacompensato-rymechanismassociatedwithmotorweaknessorCSTinjuryinpatientswithICH.
4.Futuredirection
Forthepastdecade,DTIhasbeenusedinelucidationofthemotorrecoverymechanismsinstrokepatients[1,24,25,29,31,34–36,40,41,51,54,58,77,78].However,toincreasetheusefulnessofDTIforthisresearch,sev-eralproblemsassociatedwithDTIshouldberesolved.InspiteoftheuniqueadvantagesofDTIforresearchonmotorrecoverymechanismsinstrokepatients,fewerDTIstudiesonthistopichavebeenconducted,com-paredwithstudiesusingTMSorfMRI.Tothebestofourknowledge,only13DTIstudiesonthemotorrecoverymechanismsofstrokehavebeenreported[1,24,25,29,31,34–36,40,41,51,54,58,77,78].Therefore,thetotalnumberofDTIstudiesonthistopicshouldbeincreased.Moreover,furtherstudiesonvarioustopicsassociatedwithbrainplasticityofmotorfunction,aswellasthemotorrecoverymechanismitself,shouldbeencouraged;forexample,DTIchangeswithpassageoftime,withrehabilitativeintervention,orwithmotorrecovery.
Formotorfunctioninthehumanbrain,variousneuraltractsareinvolvedandtheseneuraltractscanbegrosslyclassifiedintotheCSTandnon-CST.TheCSTismandatoryformotorfunctioninthehumanbrain.However,othernon-CSTs,suchasthereticulo-,vestibule-,andrubrospinaltracts,cancontributetomotorrecoveryafterdamagetotheCSTfollowingstroke[16,37,79].However,analysisofthenon-CSThasbeenimpossible;therefore,DTImethodsforiden-tificationandestimationofthenon-CSTshouldbede-veloped.Moreover,studiesontheaberrantmotorpath-wayalsoshouldbeinvited.
SomelimitationsofDTIneedtobeconsidered.First,thefibertrackingtechniqueisoperator-dependent.Sec-ond,DTImayunderestimatethefibertractsthanelec-trophysiologicaltest.DTIisapowerfulanatomicimag-ingtoolthatcandemonstratethegrossfiberarchitec-ture,butnotthefunctionalorsynapticconnections.Therefore,majorfiberbundlessuchastheCSTcanbetherealfiberpathwaysonDTI,relayingfiberscannotbedepictedwithDTI.Third,regionsoffibercomplex-ityandcrossingpreventfullreflectionoftheunder-lyingfiberarchitecturebyDTI[30,43,55,72].There-fore,combinedstudiesusingotherbrainmappingtech-niques,suchasTMSorfMRI,wouldbenecessarytocompensateforthelimitationsofDTI.Theadvantagesofeachofthemethodsforevaluationofaneuraltractal-lowmoreaccurateestimationwhentheyareemployedconcomitantly,becausecombinationcancompensateforthelimitationsofacertainevaluationmethodand
350S.H.Jang/Areviewofdiffusiontensorimagingstudiesonmotorrecoverymechanisms
moreaccurateinformationcanbeobtained[24,25,29,34,36,77].AsaexamplefortheCST,themostidealevaluationmethodforassessmentoftheCSTwouldbecapableof:1)obtaininginformationabouttheintegrityandcourseoftheCSTandquantificationoftheCSTatthesubcorticallevelusingDTIwithDTT;2)obtaininginformationontheoriginoftheCSTatthecorticallevelusingfMRI;and3)obtaininginformationonthequantificationandcharacteristicsoftheCSTusingthemotor-evokedpotentialdeterminedbyTMS[24,25,29,34,36,77].
5.Conclusion
Inthecurrentstudy,IreviewedDTIstudiesonthemotorrecoverymechanismsofstrokeaccordingtotheclassificationofmotorrecoverymechanisms.Al-thoughDTIhasuniqueadvantagesforresearchonthemotorrecoverymechanismsofstrokepatients,only13DTIstudieshavereportedonthistopic.Therefore,DTIresearchonthistopicshouldbeencouraged.Inaddi-tion,combinedstudiesusingotherbrainmappingtech-niquesandtechnicalcomplementarymeasureswouldbenecessarytocompensateforthelimitationsofDTI.
Acknowledgement
ThisworkwassupportedbyNationalResearchFoundationofKoreaGrantfundedbytheKoreanGov-ernment(KRF-2008-314-E00173)
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