MRI-Propeller原理.ppt

PropellerMRI,InChanSong,Ph.D.SeoulNationalUniversityHospital,Contents:Propellersequence(PeriodicallyRotatedOverlappingParallelLineswithEnhancedReconstruction)MotionartifactTheoreticalbasisApplications,MotionPeriodic:cardiacmotion,respiration,bloodflowSporadic:irritablepatientsmotionTranslation,rotation,through-planeArtifactinMRIblurringandghostingCauseLongerencodingstep,Scantime=TRxmatrixxAverageLongscantime,MRimagereconstructionundertheassumptionofobjectsmotion-freeconditionduringwholekspacecoverage,Motionartifacts-MostubiquitousandnoticeableartifactsinMRIduetovoluntaryandinvoluntarymovement,andflow(blood,CSF)-Mostlyoccuralongthephaseencodedirection,sinceadjacentlinesofphase-encodedprotonsareseparatedbyaTRintervalthatcanlast3,000msecorlonger-SlightmotioncancauseachangeintherecordedphasevariationacrosstheFOVthroughouttheMRacquisitionsequence,Motionartifact:ghostandblurring,Solutionformotioncompensation-Navigatorechousagetoestimatethemotionormotionrelatedphasefromextracollecteddata-Cardiacandrespiratorygating-Respiratoryorderingofthephaseencodingprojectionsbasedonlocationinrespiratorycycle-Signalaveragingtoreduceartifactsofrandommotion-ShortTEspinechosequences(limitedtospindensity,T1-weightedscans).LongTEscans(T2weighting)aremoresusceptibletomotion,Motion(abrupt)phaseerrorpositionerrorSolutionPhaseinformationNavigationMotioncorrectionbyphaseinformation,KeyideasinpropellersequenceKspace:partialcoveringforwholeimageMotiondetection:bladeusageCorrection:FFTpropertiesusage,DiagramofthePROPELLERcollectionreconstructionprocessformotioncorrectedMRI.,Dataacquisition,PhaseCorrect,Redundantdatamustagree,removephasefromeachbladeimageImperfectgradientbalancing,Eddycurrenteffect:echocentershift,JamesG.Pipe,Windowing,Before,After,Phasecorrection,BulkTransformationCorrectionFouriertransformcorrespondenceImagespacekspaceTranslationPhaserollRotationRotationSeparateestimationofrotationandtranslation,rotateimagerotatedata,FourierTransformProperties,Reference(onlyinnercircle),Magnitudeoftheaverageofstrips,Rotation(onlyinnercircle),Correlation,Rotationcorrection(magnitudeimage),BladebybladeoperationRotationatmaximumcorrelationCorrection,FourierTransformProperties,shiftimagephaserollacrossdata,bisbladeimage,risreferenceimage,maxatDx,TranslationComplexaveragek-spacedata,Reference(onlyinnercircle),Complexoftheaverageofstrips,InverseFT(maximum),Multiplication,BladebybladeoperationTranslationatmaximumcorrelationCorrection,BladeCorrelationthrowoutbadordifficulttointerpolate-data,Through-planemotion:lowweightingcoeff.,Reconstruction(FFT)non-Cartesiansamplingrequiresgriddingconvolution,w/motioncorrection,nocorrection,correlationcorrectiononly,motioncorrectiononly,fullcorrections,T2-FSE,T2-Propeller,T2-Propeller(corrected),Artifactreductionduetoheadmotion,DWI-EPIB=1000s/mm2,DWI-Propeller(FSE),JamesGPipe,2002,DWI(b=700s/mm2),a.EPI(TR/TE/avg=2700/113/15),b.PropellerEPI(TR/TE/blade=1600/70/26),WangFN,2005,UsefulapplicationinpropellersequenceMotion-orBo-inhomogeneitiesinsensitiveIrritablepatientDiffusionweightedimageLimitationsinpropellersequenceRedundantacquisitionLongscantime:HighSAR:probleminhigherfieldMRsystemSolutionsUndersampling(KonstantinosArfanakis,2005)ParallelimagingTurbopropeller(JamesGPipe,2006)PropellerEPI,PropellersequenceLowsensitivitytoimageartifacts,BoinhomogeneityandmotionT2-,Diffusion-weightedimages(HighSNR,lowgeometricdistortion,lowSAR),References1.PipeJ,MRM42(5):963-62,1999.2.PipeJ,etal.,MRM47(1):42-53,20023.WuY,FieldAS,AlexanderAL.ISMRM,Toronto,Canada,2003.2125.4.RobertsTP,HaiderM.IS