DKI-英文簡(jiǎn)介-課件

DiffusionalKurtosisImagingDKI英文簡(jiǎn)介DKI英文簡(jiǎn)介ppt課件2021/3/261DiffusionalKurtosisImagingDKDKI英文簡(jiǎn)介

DWI(diffusionweightedimaging)DTI(diffusiontensorimaging)DKI(diffusionkurtosisimaging)DKI英文簡(jiǎn)介ppt課件2021/3/262DKI英文簡(jiǎn)介DWI(diffDKI英文簡(jiǎn)介MR圖像的信號(hào)組織T1、T2馳豫時(shí)間、H1的密度、分子彌散運(yùn)動(dòng)DWI圖像利用擴(kuò)散敏感梯度脈沖將水分子彌散效應(yīng)擴(kuò)大，來研究不同組織中水分子擴(kuò)散運(yùn)動(dòng)的差異

DKI英文簡(jiǎn)介ppt課件2021/3/263DKI英文簡(jiǎn)介MR圖像的信號(hào)DKI英文簡(jiǎn)介通過兩個(gè)以上不同彌散敏感梯度值（b值）的彌散加權(quán)象，可計(jì)算出彌散敏感梯度方向上水分子的表觀彌散系數(shù)（apparentdiffusioncoefficient

ADC）

ADC=In(S低/S高)/(b高-b低)彌散敏感系數(shù)(b)值==r2σ2g2(△-σ/3)b值的取值范圍為0~10000s/mm2，較大的b值具有較大的彌散權(quán)重，對(duì)水分子的彌散運(yùn)動(dòng)越敏感，并引起較大的信號(hào)下降，但b值越大，圖像信噪比也相應(yīng)下降，如果b值太小，易受T2加權(quán)的影像，產(chǎn)生所謂的T2透射效應(yīng)(T2shinethrougheffect)，一般來說用大b值差的圖像測(cè)得的ADC值較準(zhǔn)確，故側(cè)ADC值時(shí)宜選較高b值和較大的b值差A(yù)DC反映了水分子的擴(kuò)散運(yùn)動(dòng)的能力,指水分子單位時(shí)間內(nèi)擴(kuò)散運(yùn)動(dòng)的范圍，越高代表水分子擴(kuò)散能力越強(qiáng)。DKI英文簡(jiǎn)介ppt課件2021/3/264DKI英文簡(jiǎn)介通過兩個(gè)以上不同彌散敏感梯度值（b值）的DKI英文簡(jiǎn)介

均質(zhì)介質(zhì)中可以水分子的自由運(yùn)動(dòng)為各向同性，即在各個(gè)方向上的彌散強(qiáng)度大小一致，彌散張量D描述為球形，沿磁共振的三個(gè)主坐標(biāo)的特征值為λ1=λ2=λ3在腦白質(zhì)中由于髓鞘的阻擋，水分子的彌散被限制在與纖維走行一致的方向上，具有較高的各向異性，此時(shí)彌散張量可表示為橢球形，其特征值λ1>λ2>λ3，最大特征值對(duì)應(yīng)的方向與經(jīng)過該體素的纖維束走行平行DKI英文簡(jiǎn)介ppt課件2021/3/265DKI英文簡(jiǎn)介均質(zhì)介質(zhì)中可以水分子的自由運(yùn)動(dòng)為各向同性，DKI英文簡(jiǎn)介ConventionalDTIfailstofullyutilizetheMRdiffusionmeasurementsthatareinherenttotissuemicrostructure.

DTIcomputesapparentdiffusivitybasedontheassumptionthatdiffusionweighted(DW)MRsignalhasamonoexponentialdependenceonthediffusionfactor(b-value).DTIimplicitlyassumesthatwatermoleculediffusionoccursinafreeandunrestrictedenvironmentwithaGaussiandistributionofdiffusiondisplacement.DKI英文簡(jiǎn)介ppt課件2021/3/266DKI英文簡(jiǎn)介ConventionalDTIfailsDKI英文簡(jiǎn)介

Inbiologicaltissue,complexcellularmicrostructuresmakewaterdiffusionahighlyhinderedorrestrictedprocess.

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

DKI英文簡(jiǎn)介ppt課件2021/3/267DKI英文簡(jiǎn)介Inbiologicaltissue,DKI英文簡(jiǎn)介Asaresult,DTIquantitationisb-valuedependentandDTIfailstofullyutilizethediffusionmeasurementsthatareinherenttotissuemicrostructure.DKI英文簡(jiǎn)介ppt課件2021/3/268DKI英文簡(jiǎn)介Asaresult,DTIquantDKI英文簡(jiǎn)介Kurtosisherereferstotheexcesskurtosisthatisthenormalizedandstandardizedfourthcentralmomentofthewaterdisplacementdistribution.ItisadimensionlessmeasurethatquantifiesthedeviationofthewaterdiffusiondisplacementprotheGaussiandistributionofunrestricteddiffusion,providingameasureofthedegreeofdiffusionhindranceorrestriction.fourthcentralmoment:四階中心距，主要用來衡量隨機(jī)分布變量的分布在均值附近的陡峭程度SincethedeviationfromGaussianbehaviorisgovernedbythecomplexityofthetissuewithinwhichthewaterisdiffusing,thisexcessdiffusionalkurtosiscanberegardedasameasureofatissue’sdegreeofstructure.DKI英文簡(jiǎn)介ppt課件2021/3/269DKI英文簡(jiǎn)介KurtosisherereferstDKI英文簡(jiǎn)介Meankurtosis(MK),theaverageapparentkurtosisalongalldiffusiongradientencodingdirections,hasbeenmeasuredanddemonstratedtoofferanimprovedsensitivityindetectingdevelopmentalandpathologicalchangesinneuraltissuesascomparedtoconventionalDTI.Inaddition,directionalkurtosisanalysishasbeenformulatedtorevealdirectionallyspecificinformation,suchasthewaterdiffusionkurtosesalongthedirectionparallelorperpendiculartotheprinciplewaterdiffusiondirectionasdeterminedbythe2nd-orderdiffusiontensorDKI英文簡(jiǎn)介ppt課件2021/3/2610DKI英文簡(jiǎn)介Meankurtosis(MK),thDKI英文簡(jiǎn)介DKIprovidesahigher-orderdescriptionofrestrictedwaterdiffusionprocessbya2nd-order3Ddiffusivitytensor(DTasinconventionalDTI)togetherwitha4th-order3Dkurtosistensor(KT).DKI英文簡(jiǎn)介ppt課件2021/3/2611DKI英文簡(jiǎn)介DKIprovidesahigher-DKI英文簡(jiǎn)介Themethodisbasedonthesametypeofpulsesequencesemployedforconventionaldiffusion-weightedimaging(DWI),buttherequiredbvaluesaresomewhatlargerthanthoseusuallyusedtomeasurediffusioncoefficients.Inthebrain,bvaluesofabout2000s/mm2aresufficient.Atleast15non-collinearandnon-coplanardirectionsarerequiredtoconstructKT.DKI英文簡(jiǎn)介ppt課件2021/3/2612DKI英文簡(jiǎn)介ThemethodisbasedonDKI英文簡(jiǎn)介DKIhasacloserelationshiptoq-spaceimagingtechniques.q-spaceimagingmethodshaveindeedrecentlybeenemployedtoestimatediffusionalkurtosis.Theprincipaldifferencebetweenthemisthatq-spaceimagingseekstoestimatethefulldiffusiondisplacementprobabilitydistributionratherthanjustthekurtosis.Asaconsequence,q-spaceimagingismoredemandingintermsofimagingtimeandgradientstrengths.MeasuringthediffusionalkurtosisrequiresonlymodestincreasesinbvaluesAndDKIislessdemandingintermsofhardwarerequirementsandpostprocessingeffort.DKI英文簡(jiǎn)介ppt課件2021/3/2613DKI英文簡(jiǎn)介DKIhasacloserelatiDKI英文簡(jiǎn)介MK(meankurtosis):MKisameasureoftheoverallkurtosis.Itdoesnothaveanydirectionalspecificity.MK的大小取決于感興趣區(qū)內(nèi)組織的結(jié)構(gòu)復(fù)雜程度，結(jié)構(gòu)越復(fù)雜非正態(tài)分布水分子擴(kuò)散受限越顯著，MK也即越大K∥(Axialkurtosis)andK⊥(Radialkurtosis)

:canbedefinedasthekurtosisparallelandperpendiculartotheprinciplediffusioneigenvector(e1)K⊥越大表明在該方向非正態(tài)分布水分子擴(kuò)散受限越明顯，反之則表明擴(kuò)散受限越弱FAK(fractionalanisotropyofkurtosis)SimilartoFAinDTI,theanisotropyofdirectionalkurtosiscanbeconvenientlydefinedasFAK

KA越小即表示越趨于各向同性擴(kuò)散;若組織結(jié)構(gòu)越緊密越規(guī)則，KA越大DKI英文簡(jiǎn)介ppt課件2021/3/2614DKI英文簡(jiǎn)介MK(meankurtosis):MKiDKI英文簡(jiǎn)介DKI英文簡(jiǎn)介ppt課件2021/3/2615DKI英文簡(jiǎn)介DKI英文簡(jiǎn)介ppt課件2021/3/2DKI英文簡(jiǎn)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英文簡(jiǎn)介ppt課件2021/3/2616DKI英文簡(jiǎn)介TypicalDKI-derivedpaDKI英文簡(jiǎn)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英文簡(jiǎn)介ppt課件2021/3/2617DKI英文簡(jiǎn)介For(a),rawDWIswereDKI英文簡(jiǎn)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英文簡(jiǎn)介ppt課件2021/3/2618DKI英文簡(jiǎn)介For(b),rawDWIswereDKI英文簡(jiǎn)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英文簡(jiǎn)介ppt課件2021/3/2619DKI英文簡(jiǎn)介For(c),rawDWIswerDKI英文簡(jiǎn)介

HigherMKisfoundinWM,indicatingagenerallyhigherdegreeofdiffusioncomplexityandrestrictionintheWMstructures.ItcanbeseenfromthedirectionalkurtosismapsthatsuchhighMKinWMismainlycontributedbyK⊥.ThissuggeststheexistenceofheterogeneityandrestricteddiffusioninaxonalstructuresBothMKandK⊥

exhibitstrongcontrastbetweenWMandGMstructures.DKI英文簡(jiǎn)介ppt課件2021/3/2620DKI英文簡(jiǎn)介HigherMKisfoundinDKI英文簡(jiǎn)介BothMKandK⊥

exhibitstrongcontrastbetweenWMandGMstructures.PositivemeananddirectionalkurtosesareobservedinbothWMandGM,indicatingfasterDWsignaldecayatlowerb-valuesandrestricteddiffusionenvironmentinbothWMandGMunderinvivoandformalin-fixedconditions.DKI英文簡(jiǎn)介ppt課件2021/3/2621DKI英文簡(jiǎn)介BothMKandK⊥exhibitDKI英文簡(jiǎn)介Thebreakdownsofneurofilamentsandmicrotubulescausedbyfixativesarebelievedtoproducemorediffusionbarriersandhenceleadtotheλ//

decreaseandK//

increase.Otherfixationeffectssuchastissueshrinkage,decreaseinmembranepermeability,increaseinaxonalpackingdensityandreductionofextracellularspaceinparenchymaalsolikelycontributetothesignificantλ⊥decreaseandK⊥

increase.DKI英文簡(jiǎn)介ppt課件2021/3/2622DKI英文簡(jiǎn)介ThebreakdownsofneurDKI英文簡(jiǎn)介TheinflammatoryneurodegenerativediseaseEAE

ischaracterizedbybothaxonallossanddemyelinationInrecentDKIstudies,therearepromisingresultsofusingMKtodetectchangesinnormalorpathologicalneuraltissue

However,asanaverageofkurtosesalongallthediffusiondirections,MKcanlosesensitivityandspecificityinprobingdirectionalchangesofpathologicaltissueDKI英文簡(jiǎn)介ppt課件2021/3/2623DKI英文簡(jiǎn)介TheinflammatoryneuroDKI英文簡(jiǎn)介K//

isfoundtobesignificantlyincreasedandλ//

decreasedinthelesionareaλ//

reductionislikelyduetocytoskeletalperturbationordebrisformationwhentheaxonalstructuresbreakdownInaddition,λ⊥

increaseswhereasK⊥

decreaseslikelybecauseofthedemyelinationandaxonallossthatalsoleadtolessdiffusionrestrictioninradialdirection.DKI英文簡(jiǎn)介ppt課件2021/3/2624DKI英文簡(jiǎn)介K//isfoundtobesigDKI英文簡(jiǎn)介ThedirectionallyaveragedMDandMKarefoundtobelesssensitivetoEAEpathologyduetotheoppositetrendsofdiffusivityandkurtosischangesinaxialandradialdirection.DKI英文簡(jiǎn)介ppt課件2021/3/2625DKI英文簡(jiǎn)介ThedirectionallyaverDKI英文簡(jiǎn)介CC:corpuscallosum（胼胝體）;EC:externalcapsule（外囊）;CP:cerebralpeduncle（大腦腳）;AC:anteriorcommissure;（前聯(lián)合）CT:cerebralcortex（腦皮質(zhì)）;HP:hippocampus（海馬）;CPu:caudateputamen（新紋狀體）DKI英文簡(jiǎn)介ppt課件2021/3/2626DKI英文簡(jiǎn)介CC:corpuscallosum（胼胝DKI英文簡(jiǎn)介Thesensitivityofλ//

indetectingratbrainWMmaturationisgenerallyobservedtobethehighestatlowb-value

Atrelativelylowb-values,theapparentdiffusivityisprimarilycontributedfromthefastwaterdiffusionactivitiesinextracellularspacethatdependonbothcellularmicrostructureandmembranepermeability.

Theuseoflowb-valuecanbestdetectthesechanges.Thehighλ//

sensitivityatlowb-valueobservedinthecurrentstudysuggeststhealterationsofthesefastwaterdiffusionactivitiesalongaxonaldirectionduringbrainmaturation.

Suchalterationsmayresultfromtheincreaseinpackingdensityoffiberbundlesandaxons,axonaldiameterincrease,changesinneurofibrils,andincreasedcomplexityofextracellularmatrix.DKI英文簡(jiǎn)介ppt課件2021/3/2627DKI英文簡(jiǎn)介Thesensitivityofλ//DKI英文簡(jiǎn)介Whereasthatofλ?

isthehighestathighb-valueThediffusionchangesprobedinWMusinghighb-valuesareascribedmoretotheslowwatermoleculediffusionparticularlyalongtheradialdirectionwhentraversingthemembranesandmyelinsheathsThehighsensitivityofλ?

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

Bothλ//

andK//

ofWMarefoundtoincreaseswithage,whichmayarisefromvariousbiologicaleventsduringearlypostnatalbrainmaturation.TheincreaseofdiffusivitycanbecausedbyaxoplasmicflowduringthemyelinationperiodneuronallossandaxonalpruningthatshortenstheaxonlengthcanleadtoanincreaseofrestrictionDKI英文簡(jiǎn)介ppt課件2021/3/2631DKI英文簡(jiǎn)介Bothλ//andK//ofWDKI英文簡(jiǎn)介TheincreaseofK⊥

inWMislikelyascribedtothemyelinationandmodificationofaxonalstructuresthatincreasesrestrictionintheradialdirection.

DKIanalysisalsorevealsthatdiffusionrestrictionintherelativelyisotropicGMincreaseswithage.ThismayreflectthemoredenselypackedstructuresandthedendriticarchitecturalmodificationinGMDKI英文簡(jiǎn)介ppt課件2021/3/2632DKI英文簡(jiǎn)介TheincreaseofK⊥inDKI英文簡(jiǎn)介

WhenthereisalargeK,theestimateddiffusivityinconventionalDTIshowsalargediscrepancywiththediffusivityestima