超声彩色多普勒.ppt

DopplerPrinciplesColorPrinciples,TheDifferences,InGrayscale,strongechoreflectionscausepixelstobedisplayed.InColorandDoppler,changesinfrequencycausepixelstobecolored.,ADopplerProcessor,TheDopplerprocessorputsadotonthe“spectrum”basedonthevelocityofamovingobject.,DopplerProcessor,Whenthereareobjectsmovingatdifferentspeeds,theDopplerprocessordisplaysadotforeachobject.,DopplerProcessor,Theverticalpositionrepresentstheobjectsvelocity.,DopplerProcessor,Whenseveralobjectsmoveatthesamevelocity,thecorrespondingdotonthespectrumisbrighter.,DopplerProcessor,DopplerInformation,Velocity,Turbulence,Intensity,Thereare3keypiecesofinformationinaDopplersignal,Ingeneral,flowtowardthetransducerwillbeabovethebaseline,andflowawayfromthetransducerwillbebelowthebaseline.,PopQuiz,1.Describe3keydifferencesbetweenthetwoDopplerWaveformsbelow.2.Matchthewaveformwiththesamplevolumeposition.,A,B,TheAngleProblem,Iftheflowisntparalleltotheultrasoundbeam,theultrasoundsystemonlyseesaportionofthevelocity.,ActualVelocity,ApparentVelocity,TheAngleProblem,Thetransduceronly“sees”aportionofthetotalvelocity.,TheAngleProblem,Ontheotherside,theapparentdirectionappearstobeopposite,eventhoughtheflowdirectionisthesame!,TheAngleProblem,Andinthecenter.thereisNOapparentflow.Dopplerprocessorscannotseeflowperpendiculartotheultrasoundbeam.,TheDopplerEquation,Dontmemorizethis.Butrememberacoupleofrulesofthumb:WHATSOWHATTheapparentvelocityisYouwontgetmuchflowwhendependentontheangle()theangleisnear90ThehigherthetransmitLowerfrequencyprobesarefrequency(ft),thelowertheusedtomeasurehigherdetectedvelocityvelocities,v=,fdc,2ftcos,TheAliasingProblem,Whatifyoucheckedyourclockevery5seconds.whatwouldyouseeonthesecondhand?,1,2,3,4,TheAliasingProblem,Whathappensifyoulookatthesameclockevery55seconds?,PopQuiz,Howoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?,12,PopQuiz,Howoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?,12,6,Every29.99999seconds,PopQuiz,Howfastcantheclockbe,ifyouregoingtoaccuratelydemonstrateitsdirectionwhenyoulookatitevery15seconds?,PopQuiz,Howfastcantheclockbe,ifyouregoingtoaccuratelydemonstrateitsdirectionwhenyoulookatitevery15seconds?,60sec.clock,PopQuiz,Howfastcantheclockbe,ifyouregoingtoaccuratelydemonstrateitsdirectionwhenyoulookatitevery15seconds?,60sec.clock,50sec.clock,PopQuiz,Howfastcantheclockbe,ifyouregoingtoaccuratelydemonstrateitsdirectionwhenyoulookatitevery15seconds?,60sec.clock,50sec.clock,40sec.clock,PopQuiz,Howfastcantheclockbe,ifyouregoingtoaccuratelydemonstrateitsdirectionwhenyoulookatitevery15seconds?,60sec.clock,50sec.clock,40sec.clock,30sec.clock,?,PopQuiz,Howfastcantheclockbe,ifyouregoingtoaccuratelydemonstrateitsdirectionwhenyoulookatitevery15seconds?,Nofasterthanonerotationevery30seconds.,60sec.clock,50sec.clock,40sec.clock,30sec.clock,20sec.clock,?,PopQuiz,Whatifyoulookedattheclockevery10seconds?,PopQuiz,Whatifyoulookedattheclockevery10seconds?,Nofasterthanonerotationevery20seconds.Thefasteryousample,thefastertheclockcanbe.,50sec.clock,40sec.clock,30sec.clock,20sec.clock,15sec.clock,?,TheAliasingProblem,PulsedDopplerhasthelimitationthatthemaximumvelocityisdeterminedbythe“samplingrate.”ThesamplingrateisknownasthePRF,pulserepetitionfrequency.Ifthevelocityistoohigh,theflowwillappeartogobackwards,justliketheclock.,DopplerSummary,ThreeKeyPiecesofInformationinaDopplerSignalVelocityIntensityTurbulenceIngeneral,flowtowardthetransducerisabovethebaseline,flowawayisbelowthebaseline.Majorlimitationismaximumvelocity,whichisbasedonfrequencyandsamplingrate.2ndlimitationistheangleofflowrelativetothetransducer.,ColorDoppler,ColorDopplerusesthesameprincipals.ThesystemacquiresaDopplerSpectrumfrommanypointsintheimage.Foreachpoint,thesystemdeterminestheaveragevelocity.Theaveragevelocityisconvertedtoacolor.GenerallyREDtowardthetransducerandBLUEaway.,AnatomyofaColorFlowImage,Theresultisanimagewithcolorsrepresentingtheaveragevelocities.,Generaldirectionofultrasoundbeam,AnatomyofaColorFlowImage,Theresultisanimagewithcolorsrepresentingtheaveragevelocities.,Generaldirectionofultrasoundbeam,Thisareaisblue,soflowisgenerallyawayfromthebeam,lefttoright,RABT,AnatomyofaColorFlowImage,Theresultisanimagewithcolorsrepresentingtheaveragevelocities.,Generaldirectionofultrasoundbeam,Thisareaisred,soflowisawaythebeam,righttoleft,Thisareaisblue,soflowisgenerallytowardsfromthebeam,lefttoright,RABT,DealingwiththeDopplerProblems,Whatisgoingonhere?Whyisthebloodflowmulti-colored,ratherthanallredorallblue?,ColorFlowhasDopplersLimitations,OfthethreepiecesofinformationfromaDopplersignal,CFMusesonlytheVELOCITYinformation.VelocityIntensityTurbulenceAndhasthesamelimitations:Aliasing:MaximumvelocitylimitedbyPRFDependentonangleofflow,FrameRatesareaproblemtoo!,SinceColorFlowrequireslotsofDopplersignals,theframeratescanbeslow.Youronlychoicesare:Dolesscolorflow(makethecolorboxsmaller)CheatL500:ParallelProcessingL400:AutomaticControlTechnology,DealingwiththeDopplerProblems,Whatisgoingonhere?Whereistheflowvelocitythehighest?A?B?C?,A,B,C,DealingwiththeDopplerProblems,Theflowvelocityisthesameinthevessel,buttheanglemakesitlooklikethebloodisacceleratingfromAtoBtoC.,Whatisgoingonhere?Whereistheflowvelocitythehighest?A?B?C?,A,B,C,DealingwiththeDopplerProblems,Whatisgoingonhere?Whyisthebloodflowmulti-colored,ratherthanallredorallblue?,DealingwiththeDopplerProblems,Whatisgoingonhere?Whyisthebloodflowmulti-colored,ratherthanallredorallblue?,Itsacombinationofchanginganglesandaliasing.,DealingwiththeDopplerProblems,Rememberthis?WhatifweusedIntensityinsteadofVelocitytomaptheflowinformation?,DealingwiththeDopplerProblems,Velocityasks“howfastisitgoing?”Velocityissubjecttoangleproblems.Apparentvelocitychangeswithangle.Velocityissubjecttoaliasing.DependsonPRF.,Intensityasks“howmanyaregoing?”Intensityisnotsubject