DKI-英文简介-课件

DiffusionalKurtosisImagingDKI英文简介DKI英文简介ppt课件2021/3/261DiffusionalKurtosisImagingDKDKI英文简介

DWI(diffusionweightedimaging)DTI(diffusiontensorimaging)DKI(diffusionkurtosisimaging)DKI英文简介ppt课件2021/3/262DKI英文简介DWI(diffDKI英文简介MR图像的信号组织T1、T2驰豫时间、H1的密度、分子弥散运动DWI图像利用扩散敏感梯度脉冲将水分子弥散效应扩大，来研究不同组织中水分子扩散运动的差异

DKI英文简介ppt课件2021/3/263DKI英文简介MR图像的信号DKI英文简介通过两个以上不同弥散敏感梯度值（b值）的弥散加权象，可计算出弥散敏感梯度方向上水分子的表观弥散系数（apparentdiffusioncoefficient

ADC）

ADC=In(S低/S高)/(b高-b低)弥散敏感系数(b)值==r2σ2g2(△-σ/3)b值的取值范围为0~10000s/mm2，较大的b值具有较大的弥散权重，对水分子的弥散运动越敏感，并引起较大的信号下降，但b值越大，图像信噪比也相应下降，如果b值太小，易受T2加权的影像，产生所谓的T2透射效应(T2shinethrougheffect)，一般来说用大b值差的图像测得的ADC值较准确，故侧ADC值时宜选较高b值和较大的b值差ADC反映了水分子的扩散运动的能力,指水分子单位时间内扩散运动的范围，越高代表水分子扩散能力越强。DKI英文简介ppt课件2021/3/264DKI英文简介通过两个以上不同弥散敏感梯度值（b值）的DKI英文简介

均质介质中可以水分子的自由运动为各向同性，即在各个方向上的弥散强度大小一致，弥散张量D描述为球形，沿磁共振的三个主坐标的特征值为λ1=λ2=λ3在脑白质中由于髓鞘的阻挡，水分子的弥散被限制在与纤维走行一致的方向上，具有较高的各向异性，此时弥散张量可表示为椭球形，其特征值λ1>λ2>λ3，最大特征值对应的方向与经过该体素的纤维束走行平行DKI英文简介ppt课件2021/3/265DKI英文简介均质介质中可以水分子的自由运动为各向同性，DKI英文简介ConventionalDTIfailstofullyutilizetheMRdiffusionmeasurementsthatareinherenttotissuemicrostructure.

DTIcomputesapparentdiffusivitybasedontheassumptionthatdiffusionweighted(DW)MRsignalhasamonoexponentialdependenceonthediffusionfactor(b-value).DTIimplicitlyassumesthatwatermoleculediffusionoccursinafreeandunrestrictedenvironmentwithaGaussiandistributionofdiffusiondisplacement.DKI英文简介ppt课件2021/3/266DKI英文简介ConventionalDTIfailsDKI英文简介

Inbiologicaltissue,complexcellularmicrostructuresmakewaterdiffusionahighlyhinderedorrestrictedprocess.

Non-monoexponentialdecaysareexperimentallyobservedinbothwhitematterandgraymatter.Moreover,thesimplifieddescriptionofthediffusionprocessinvivobya2nd-order3DdiffusivitytensorpreventsDTIfrombeingtrulyeffectiveincharacterizingrelativelyisotropictissuesuchasGM.EveninWM,theDTImodelcanfailifthetissuecontainssubstantialcrossingordivergingfibers.

DKI英文简介ppt课件2021/3/267DKI英文简介Inbiologicaltissue,DKI英文简介Asaresult,DTIquantitationisb-valuedependentandDTIfailstofullyutilizethediffusionmeasurementsthatareinherenttotissuemicrostructure.DKI英文简介ppt课件2021/3/268DKI英文简介Asaresult,DTIquantDKI英文简介Kurtosisherereferstotheexcesskurtosisthatisthenormalizedandstandardizedfourthcentralmomentofthewaterdisplacementdistribution.ItisadimensionlessmeasurethatquantifiesthedeviationofthewaterdiffusiondisplacementprotheGaussiandistributionofunrestricteddiffusion,providingameasureofthedegreeofdiffusionhindranceorrestriction.fourthcentralmoment:四阶中心距，主要用来衡量随机分布变量的分布在均值附近的陡峭程度SincethedeviationfromGaussianbehaviorisgovernedbythecomplexityofthetissuewithinwhichthewaterisdiffusing,thisexcessdiffusionalkurtosiscanberegardedasameasureofatissue’sdegreeofstructure.DKI英文简介ppt课件2021/3/269DKI英文简介KurtosisherereferstDKI英文简介Meankurtosis(MK),theaverageapparentkurtosisalongalldiffusiongradientencodingdirections,hasbeenmeasuredanddemonstratedtoofferanimprovedsensitivityindetectingdevelopmentalandpathologicalchangesinneuraltissuesascomparedtoconventionalDTI.Inaddition,directionalkurtosisanalysishasbeenformulatedtorevealdirectionallyspecificinformation,suchasthewaterdiffusionkurtosesalongthedirectionparallelorperpendiculartotheprinciplewaterdiffusiondirectionasdeterminedbythe2nd-orderdiffusiontensorDKI英文简介ppt课件2021/3/2610DKI英文简介Meankurtosis(MK),thDKI英文简介DKIprovidesahigher-orderdescriptionofrestrictedwaterdiffusionprocessbya2nd-order3Ddiffusivitytensor(DTasinconventionalDTI)togetherwitha4th-order3Dkurtosistensor(KT).DKI英文简介ppt课件2021/3/2611DKI英文简介DKIprovidesahigher-DKI英文简介Themethodisbasedonthesametypeofpulsesequencesemployedforconventionaldiffusion-weightedimaging(DWI),buttherequiredbvaluesaresomewhatlargerthanthoseusuallyusedtomeasurediffusioncoefficients.Inthebrain,bvaluesofabout2000s/mm2aresufficient.Atleast15non-collinearandnon-coplanardirectionsarerequiredtoconstructKT.DKI英文简介ppt课件2021/3/2612DKI英文简介ThemethodisbasedonDKI英文简介DKIhasacloserelationshiptoq-spaceimagingtechniques.q-spaceimagingmethodshaveindeedrecentlybeenemployedtoestimatediffusionalkurtosis.Theprincipaldifferencebetweenthemisthatq-spaceimagingseekstoestimatethefulldiffusiondisplacementprobabilitydistributionratherthanjustthekurtosis.Asaconsequence,q-spaceimagingismoredemandingintermsofimagingtimeandgradientstrengths.MeasuringthediffusionalkurtosisrequiresonlymodestincreasesinbvaluesAndDKIislessdemandingintermsofhardwarerequirementsandpostprocessingeffort.DKI英文简介ppt课件2021/3/2613DKI英文简介DKIhasacloserelatiDKI英文简介MK(meankurtosis):MKisameasureoftheoverallkurtosis.Itdoesnothaveanydirectionalspecificity.MK的大小取决于感兴趣区内组织的结构复杂程度，结构越复杂非正态分布水分子扩散受限越显著，MK也即越大K∥(Axialkurtosis)andK⊥(Radialkurtosis)

:canbedefinedasthekurtosisparallelandperpendiculartotheprinciplediffusioneigenvector(e1)K⊥越大表明在该方向非正态分布水分子扩散受限越明显，反之则表明扩散受限越弱FAK(fractionalanisotropyofkurtosis)SimilartoFAinDTI,theanisotropyofdirectionalkurtosiscanbeconvenientlydefinedasFAK

KA越小即表示越趋于各向同性扩散;若组织结构越紧密越规则，KA越大DKI英文简介ppt课件2021/3/2614DKI英文简介MK(meankurtosis):MKiDKI英文简介DKI英文简介ppt课件2021/3/2615DKI英文简介DKI英文简介ppt课件2021/3/2DKI英文简介TypicalDKI-derivedparametricmapsfromasinglesliceofa)invivo,b)formalin-fixedadultratbrainsandc)anormalhumansubject(male,44yearsold).Axialdiffusivity(λ//),radialdiffusivity(λ⊥),meandiffusivity(MD),axialkurtosis(K//),radialkurtosis(K⊥),meankurtosis(MK),fractionalanisotropy(FA),directionallyencodedcolourFA(DEC-FA)andfractionalanisotropyofkurtosis(FAK)mapsarecomputedfromDKImodel.DKI英文简介ppt课件2021/3/2616DKI英文简介TypicalDKI-derivedpaDKI英文简介For(a),rawDWIswereacquiredbySEEPIwithTR/TE = 3000/30.3 ms,δ/Δ = 5/17 ms,slicethickness = 1 mm,FOV = 30 × 30 mm2,datamatrix = 128 × 128(zerofilledto256 × 256),NEX = 4,6b-values(0.0,0.5,1.0,1.5,2.0and2.5 ms/µm2)andalong30directionsusing7TscannerDKI英文简介ppt课件2021/3/2617DKI英文简介For(a),rawDWIswereDKI英文简介For(b),rawDWIswereacquiredwiththesameparametersasthoseforinvivoexceptTE = 34.3 ms,δ = 9 msandb-valuesof0.0,1.0,2.0,3.0,4.0and5.0 ms/µm2.Alargerb-valuerangewasusedinexvivoexperimentduetothegenerallylowerdiffusivities.DKI英文简介ppt课件2021/3/2618DKI英文简介For(b),rawDWIswereDKI英文简介

For(c),rawDWIswereacquiredbySEEPIwithTR/TE = 2300/109 ms,slicethickness = 2 mm,FOV = 256 × 256 mm2,datamatrix = 128 × 128,NEX = 2,6b-values(0.0,0.5,1.0,1.5,2.0and2.5 ms/µm2)andalong30directionsusinga3TSiemensscannerDKI英文简介ppt课件2021/3/2619DKI英文简介For(c),rawDWIswerDKI英文简介

HigherMKisfoundinWM,indicatingagenerallyhigherdegreeofdiffusioncomplexityandrestrictionintheWMstructures.ItcanbeseenfromthedirectionalkurtosismapsthatsuchhighMKinWMismainlycontributedbyK⊥.ThissuggeststheexistenceofheterogeneityandrestricteddiffusioninaxonalstructuresBothMKandK⊥

exhibitstrongcontrastbetweenWMandGMstructures.DKI英文简介ppt课件2021/3/2620DKI英文简介HigherMKisfoundinDKI英文简介BothMKandK⊥

exhibitstrongcontrastbetweenWMandGMstructures.PositivemeananddirectionalkurtosesareobservedinbothWMandGM,indicatingfasterDWsignaldecayatlowerb-valuesandrestricteddiffusionenvironmentinbothWMandGMunderinvivoandformalin-fixedconditions.DKI英文简介ppt课件2021/3/2621DKI英文简介BothMKandK⊥exhibitDKI英文简介Thebreakdownsofneurofilamentsandmicrotubulescausedbyfixativesarebelievedtoproducemorediffusionbarriersandhenceleadtotheλ//

decreaseandK//

increase.Otherfixationeffectssuchastissueshrinkage,decreaseinmembranepermeability,increaseinaxonalpackingdensityandreductionofextracellularspaceinparenchymaalsolikelycontributetothesignificantλ⊥decreaseandK⊥

increase.DKI英文简介ppt课件2021/3/2622DKI英文简介ThebreakdownsofneurDKI英文简介TheinflammatoryneurodegenerativediseaseEAE

ischaracterizedbybothaxonallossanddemyelinationInrecentDKIstudies,therearepromisingresultsofusingMKtodetectchangesinnormalorpathologicalneuraltissue

However,asanaverageofkurtosesalongallthediffusiondirections,MKcanlosesensitivityandspecificityinprobingdirectionalchangesofpathologicaltissueDKI英文简介ppt课件2021/3/2623DKI英文简介TheinflammatoryneuroDKI英文简介K//

isfoundtobesignificantlyincreasedandλ//

decreasedinthelesionareaλ//

reductionislikelyduetocytoskeletalperturbationordebrisformationwhentheaxonalstructuresbreakdownInaddition,λ⊥

increaseswhereasK⊥

decreaseslikelybecauseofthedemyelinationandaxonallossthatalsoleadtolessdiffusionrestrictioninradialdirection.DKI英文简介ppt课件2021/3/2624DKI英文简介K//isfoundtobesigDKI英文简介ThedirectionallyaveragedMDandMKarefoundtobelesssensitivetoEAEpathologyduetotheoppositetrendsofdiffusivityandkurtosischangesinaxialandradialdirection.DKI英文简介ppt课件2021/3/2625DKI英文简介ThedirectionallyaverDKI英文简介CC:corpuscallosum（胼胝体）;EC:externalcapsule（外囊）;CP:cerebralpeduncle（大脑脚）;AC:anteriorcommissure;（前联合）CT:cerebralcortex（脑皮质）;HP:hippocampus（海马）;CPu:caudateputamen（新纹状体）DKI英文简介ppt课件2021/3/2626DKI英文简介CC:corpuscallosum（胼胝DKI英文简介Thesensitivityofλ//

indetectingratbrainWMmaturationisgenerallyobservedtobethehighestatlowb-value

Atrelativelylowb-values,theapparentdiffusivityisprimarilycontributedfromthefastwaterdiffusionactivitiesinextracellularspacethatdependonbothcellularmicrostructureandmembranepermeability.

Theuseoflowb-valuecanbestdetectthesechanges.Thehighλ//

sensitivityatlowb-valueobservedinthecurrentstudysuggeststhealterationsofthesefastwaterdiffusionactivitiesalongaxonaldirectionduringbrainmaturation.

Suchalterationsmayresultfromtheincreaseinpackingdensityoffiberbundlesandaxons,axonaldiameterincrease,changesinneurofibrils,andincreasedcomplexityofextracellularmatrix.DKI英文简介ppt课件2021/3/2627DKI英文简介Thesensitivityofλ//DKI英文简介Whereasthatofλ⟂

isthehighestathighb-valueThediffusionchangesprobedinWMusinghighb-valuesareascribedmoretotheslowwatermoleculediffusionparticularlyalongtheradialdirectionwhentraversingthemembranesandmyelinsheathsThehighsensitivityofλ⟂

athighb-valueindetectingbrainmaturationshowninthefigurelikelyreflectstheseWMmicrostructuralchanges,includingmyelinationandaxonaldensityanddiameterchangesduringpostnatalbraindevelopment.DKI英文简介ppt课件2021/3/2628DKI英文简介Whereasthatofλ⟂isDKI英文简介FAquantitationisalsoaffectedbytheb-valueanditsabilityindetectingbrainmaturationalchangesvariesamongdifferentstructures.DKI英文简介ppt课件2021/3/2629DKI英文简介FAquantitationisalsDKI英文简介Figure7ashowsthatthesensitivityoffittingallthemulti-b-valueDWIstoDTImodelisgenerallysimilartothatofemployingamediumb-value(b = 1.5 ms/µm2)showninFigure6InFigure7b,thegeneralandcontinualkurtosisincreasewithageisobserved,indicatingthatmorediffusionrestrictionoccursduringbrainmaturationinbothWMandGMstructures.TheDKI-deriveddiffusivityandkurtosisindicesarehighlysensitivetobraindevelopmentalchanges.DKI英文简介ppt课件2021/3/2630DKI英文简介Figure7ashowsthattDKI英文简介

Bothλ//

andK//

ofWMarefoundtoincreaseswithage,whichmayarisefromvariousbiologicaleventsduringearlypostnatalbrainmaturation.TheincreaseofdiffusivitycanbecausedbyaxoplasmicflowduringthemyelinationperiodneuronallossandaxonalpruningthatshortenstheaxonlengthcanleadtoanincreaseofrestrictionDKI英文简介ppt课件2021/3/2631DKI英文简介Bothλ//andK//ofWDKI英文简介TheincreaseofK⊥

inWMislikelyascribedtothemyelinationandmodificationofaxonalstructuresthatincreasesrestrictionintheradialdirection.

DKIanalysisalsorevealsthatdiffusionrestrictionintherelativelyisotropicGMincreaseswithage.ThismayreflectthemoredenselypackedstructuresandthedendriticarchitecturalmodificationinGMDKI英文简介ppt课件2021/3/2632DKI英文简介TheincreaseofK⊥inDKI英文简介

WhenthereisalargeK,theestimateddiffusivityinconventionalDTIshowsalargediscrepancywiththediffusivityestima