ConventionalT2WIDW-EPIWhyUSEDTIMRI:DetectionofAcuteStroke“DiffusionWeightedImaging(DWI)hasproventobethemosteffectivemeansofdetectingearlystrokes”LehighMagneticImagingCenter

Sodiumionpumpsfail-watergoesincellsandcannotdiffuse–DWimagegetsbright(note–muchlatercellsburstandstrokeareagetsverydark)當前1頁，總共59頁。WhyUSEDTIMRI

TumorT2(brightwater) DWI(xdirection)(T2(brightwater)+(diffusion))Contrast(T1+Gadolinium)T2(brightwater)當前2頁，總共59頁。WhyDTIMRI(morerecently):FiberTracking當前3頁，總共59頁。DiffusionWeightedImageXdirectionDavidPorter-November2000ArtifactorAbnormalityHigherdiffusioninXdirectionlowersignal 1stlevelofcomplexity當前4頁，總共59頁。RFGxGyGz-Time(gradient

strength)T2T2+diffusionT2ImageSequenceExciteMeasurediffusionRegularT2image當前5頁，總共59頁。2ndLevelofcomplexityDWI:3DirectioncourtesyofDrSorensen,MGH,BostonDavidPorter-November2000

single-shotEPIdiffusion-weighted(DW)imageswithb=1000s/mm2 anddiffusiongradientsappliedalongthreeorthogonaldirectionsHigherdiffusionlowersignalDzzDxxDyyMeasuringDiffusioninotherdirections(examples)當前6頁，總共59頁。3rdlevelofcomplexity

DiffusionTensorImagingBasicsMeasureswaterdiffusioninatleast6directionsEcho-planarimaging(fastacquisition)Collectingsmallvoxels(1.8x1.8x3mm),scanningtakesabout10minutesHowcanwetrackwhitematterfibersusingDTI當前7頁，總共59頁。UsefulforfollowingwhitemattertractsinhealthybrainHigherdiffusionlowersignalwaterDiffusionellipsoidDiffusionellipsoidWhitematterfibers當前8頁，總共59頁。IsotropicAnisotropicAdaptedfrom:Beaulieu(2002).NMRinBiomed;15:435-455HigherdiffusionlowersignalWhitematterfibers當前9頁，總共59頁。xyzDTIellipsoid

measure6directionstodescribenodiffusionEllipsoidrepresentsmagnitudeofdiffusioninalldirectionsbydistancefromcenterofellipsoidtoitssurface.當前10頁，總共59頁。PierpaoliandBasser,TowardaQuantitativeAssessmentofDiffusionAnisotropy,Magn.Reson.Med,36,893-906(1996)EllipsoidImageTractInformationavailablethroughDTI當前11頁，總共59頁。TractographyZhang&Laidlaw:/comp/proceedings/vis/2004/8788/00/87880028p.pdf.

SuperiorviewcolorfibermapsLateralviewcolorfibermaps當前12頁，總共59頁。DiffusionTensorImagingdataforcorticalspinaltractonrightsideblue=superior–inferiorfibersgreen=anterior–posteriorfibersred=right–leftfibersNotetumorisdarkermassonleftsideofaxialsliceaxialsagcorMRISC當前13頁，總共59頁。FA+color

(largestdiffusiondirection)red=right–leftgreen=anterior–posteriorblue=superior-inferior當前14頁，總共59頁。Protonspectroscopy(alsocandoC,O,Ph,..Nuclei)Lookingatprotonsinothermolecules(notwater)(ieNAA,Choline,Creatine,…….)Need >mmol/lofsubstances highgyromagneticratio()JustlikespectroscopyusedbychemistbutincludesspatiallocalizationMRS–MagneticResonanceSpectroscopy當前15頁，總共59頁。JustlookingatProtonSpectroscopyJustexcitesmallvolumeDowatersuppressionsogiantpeakdisappearsCompareremainingpeaksFrequencyFrequencyprecession當前16頁，總共59頁。MRS–MagneticResonanceSpectroscopyFrequencyofprecessionamplitudeNAACrChoNAA=N-acetylaspartate,Cr=Creatine,Cho=Choline當前17頁，總共59頁。Multi–VoxelSpectroscopy(akaChemicalShiftImaging–CSI)DomanyvoxelsatonceCanbesomedisadvantageswithsignaltonoise(S/N)and“voxelbleeding”當前18頁，總共59頁。EvaluateHealthofNeurons(NAAlevel)NormalizewithCreatine(fairlyconstantinbrain)RedmeansHighNAA/CRlevels當前19頁，總共59頁。EpilepsySeizures(effectsmetabolitelevels)findlocationdetermineonsettime當前20頁，總共59頁。OtherNucleiofinterestforSpectroscopy當前21頁，總共59頁。23NainRatBrain(lowresolutionimagesaresodium23images)(highresolutionimagesarehydrogenimages)Note:ThisslidehasnothingtodowithSpectroscopy.Itisastandardimagingslidecreatedwiththe23Nanucleusandthehydrogennucleus.Ithasbeenincludedtoshowanexampleofimagingdonewithanucleiotherthanhydrogen.當前22頁，總共59頁。CommonMetabolitesusedinProtonSpectroscopy當前23頁，總共59頁。ImportantConceptsWhatenergiesareusedineachmodality?Howdoestheenergyinteractwiththetissue?Howistheimageproduced?Whatisrepresentedintheimage?Whatareimportantadvantagesanddisadvantagesofthemajorimagingmodalities?WhatarethefundamentaldifferencesbetweentheXraytechnologies(2Dvs3D,RadiographyvsCTvsFluoroscopy)?WhatarethetwomajortypesofMRIimages(T1,T2),andhowaretheydifferent?HowareAngiogramsproduced(bothXrayandMRI)?Whyaretheadvantagesofcombiningimagingmodalities?當前24頁，總共59頁。ImportantConcepts

WhatdoesDTI,diffusiontensorimaging,measure?WhatstructuresthatweareinterestedineffectDTIimages?WhatdoestheDTIellipsoidrepresent?HowmightDTIbeusefulforclinicalapplicationorresearch?Whatarewelookingatwithprotonspectroscopy?Whatarethethreemajormetaboliteswetypicallymeasure?Whatdowe“need”tobeabletodoprotonspectroscopy?Whatmightprotonspectroscopybeusedfor?當前25頁，總共59頁。probablynouse

當前26頁，總共59頁。當前27頁，總共59頁。TractographyZhang&Laidlaw:/comp/proceedings/vis/2004/8788/00/87880028p.pdf.

SuperiorviewcolorfibermapsLateralviewcolorfibermaps當前28頁，總共59頁。G18090GechoTEAttheechotimeTE,NMRsignalisdecayedby,-T2decay(spin-spindiffusion)-diffusivemotionForanysetofdiff.gradientpulsesSignalloss:byintra-voxelphasedispersion當前29頁，總共59頁。DTIScalarParametersTrace:Magnitudeofdiffusioninavoxel.IncreasesindamagedwhitematterFractionalAnisotropy(FA):Measureofdirectionally-restricteddiffusion.DecreasesindamagedwhitematterRosenbloomM,etal.(July2004).NIAApubs;/publications/arh27-2/146-152.htm當前30頁，總共59頁。TheDiffusionTensor,DDiffusionisnotequalinalldirections(anisotropic).Usethistoprobebrainstructure!Representthediffusionpatternateachpointinthebrainusinganellipsoid.當前31頁，總共59頁。DiffusionVector(Colour)MapThethreemagnitudesofthediffusionellipsoidcanbeshownusingthreecolours(RGB).Red=Left–RightGreen=Ant.–Pos.Blue=Sup.–Inf.Mapofmajordirectionsofwatermovementinthebrain.當前32頁，總共59頁。FibreTractographyInprinciple,thelocationsofmajorwhitematterfibretractsinthebraincanbemappedusingtheinformationinthecolourmap,by“followingthearrows.”當前33頁，總共59頁。withouthindrancewithhindranceHinderedDiffusion(diffusionellipsoid)WILSON當前34頁，總共59頁。InformationavailablethroughDTI–Orientationofλ1Usefulforfollowingwhitemattertracts當前35頁，總共59頁。InformationavailablethroughDTI--AσRelatedtotheshapeoftheellipsoidIndependentofDav(normalized)Zeroforasphere,positiveforothershapesSensitivetomyelinationandcorticaldevelopmentavs當前36頁，總共59頁。DiffusionTensorImaging(As)NormalAdultBrain(Amaps)當前37頁，總共59頁。HigherdiffusionlowersignalTissueSampleA

TissueSampleBFreelyDiffusingWater=DarkLargerDRestrictedDiffusion=BrightSmallerDCELLEXTRA-CELLULARSPACEFREELYDIFFUSINGWATERINEXTRA-CELLULARSPACE當前38頁，總共59頁。K-spaceviewofthespinechoimagingKxKy123.......n當前39頁，總共59頁。XDiffusion-WeightingYDiffusion-WeightingZDiffusion-WeightingGFEGPEGSSRFDiff.Grad.alongdifferentaxisSSPEFE當前40頁，總共59頁。

DTI(DiffusionTensorImaging)courtesyofDrSorensen,MGH,BostonDavidPorter-November2000

single-shotEPIdiffusion-weighted(DW)imageswithb=1000s/mm2 anddiffusiongradientsappliedalongthreeorthogonaldirectionsHigherdiffusionlowersignal當前41頁，總共59頁。ConventionalT2WIDW-EPIDetectionofAcuteStroke“DiffusionWeightedImaging(DWI)hasproventobethemosteffectivemeansofdetectingearlystrokes”LehighMagneticImagingCenter

Sodiumionpumpsfail,watergoesincellsandcannotdiffuse.當前42頁，總共59頁。TumorT2(brightwater) DWI(xdirection)(T2(brightwater)+diffusion)T1+Gadolinium當前43頁，總共59頁。TheDiffusionTensor,DDiffusionisnotequalinalldirections(anisotropic).Usethistoprobebrainstructure!Diffusionellipsoidforeachvoxelxyz當前44頁，總共59頁。當前45頁，總共59頁。DTIScalarParametersTrace:Themagnitudeofdiffusioninavoxel.FractionalAnisotropy(FA):Theextenttowhichdiffusionisdirectionallyrestricted.當前46頁，總共59頁。UnusedslidesfromAna516lecture

當前47頁，總共59頁。PulseSequence:Gradient-Echo

DiffusionWeightinginXdirection90oExcitationImageAcquisitionRFGxGyGzG-GEPI(T2)diffusiongradients當前48頁，總共59頁。GradientCoils當前49頁，總共59頁。RFGxGyGz-TimeNODIFFUISIONwithDIFFUISIONyxprotons(Hydrogen)signal

loss當前50頁，總共59頁。DIFFUSIONMAPS

(usedtoremovespindensity,T1,T2,TR,andTEeffects)

S=S0e(-bDxx)Ln(S)=Ln(S0)–bDxxorDxx=(Ln(S0)–Ln(S))/bS0

(T2*EPI)S(T2*EPI+

weakDiffusioninXdirection)

DxxMostImportantimageweak當前51頁，總共59頁。XDiffusion-WeightingYDiffusion-WeightingZDiffusion-WeightingGFEGPEGSSRFALittleMoreDetailSSPEFExzyyxz當前52頁，總共59頁。Tracttracingproblems(fibercrossing)當前53頁，總共59頁。90oExcitationImageAcquisitionRFGxGyGzG-GDoX,Y,andZatthesametime當前54頁，總共59頁。Butwhatisadiffusiontensor?

Itisamathematicaldescriptionof