DopplerPrinciplesColorPrinciplesTheDifferencesInGrayscale,strongechoreflectionscausepixelstobedisplayed.

InColorandDoppler,changesinfrequencycausepixelstobecolored.ADopplerProcessorTheDopplerprocessorputsadotonthe“spectrum”basedonthevelocityofamovingobject.DopplerProcessorTheverticalpositionrepresentstheobject’svelocity.DopplerProcessorWhenseveralobjectsmoveatthesamevelocity,thecorrespondingdotonthespectrumisbrighter.DopplerProcessorPopQuiz1.Describe3keydifferencesbetweenthetwoDopplerWaveformsbelow.2.Matchthewaveformwiththesamplevolumeposition.AB21TheAngleProblemIftheflowisn’tparalleltotheultrasoundbeam,theultrasoundsystemonlysee’saportionofthevelocity.ActualVelocityApparentVelocityTheAngleProblemThetransduceronly“sees”aportionofthetotalvelocity.TheAngleProblemAndinthecenter...thereisNOapparentflow.Dopplerprocessorscannotseeflowperpendiculartotheultrasoundbeam.TheDopplerEquationDon’tmemorizethis.

Butrememberacoupleofrulesofthumb:

WHAT SOWHATTheapparentvelocityis Youwon’tgetmuchflowwhen

dependentontheangle() theangleisnear90°

Thehigherthetransmit Lowerfrequencyprobesare

frequency(ft),thelowerthe usedtomeasurehigher

detectedvelocity velocitiesv=fd·c2ftcosTheAliasingProblemWhatifyoucheckedyourclockevery5seconds...whatwouldyouseeonthesecondhand?1234PopQuizHowoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?12PopQuizHowoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?126Every29.99999secondsPopQuizHowfastcantheclockbe,ifyou’regoingtoaccuratelydemonstrateit’sdirectionwhenyoulookatitevery15seconds?PopQuizHowfastcantheclockbe,ifyou’regoingtoaccuratelydemonstrateit’sdirectionwhenyoulookatitevery15seconds?60sec.clock50sec.clockPopQuizHowfastcantheclockbe,ifyou’regoingtoaccuratelydemonstrateit’sdirectionwhenyoulookatitevery15seconds?60sec.clock50sec.clock40sec.clockPopQuizHowfastcantheclockbe,ifyou’regoingtoaccuratelydemonstrateit’sdirectionwhenyoulookatitevery15seconds?60sec.clock50sec.clock40sec.clock30sec.clock?PopQuizWhatifyoulookedattheclockevery10seconds?PopQuizWhatifyoulookedattheclockevery10seconds?Nofasterthanonerotationevery20seconds.Thefasteryousample,thefastertheclockcanbe.50sec.clock40sec.clock30sec.clock20sec.clock15sec.clock?ColorDopplerColorDopplerusesthesameprincipals.

ThesystemacquiresaDopplerSpectrumfrommanypointsintheimage.

Foreachpoint,thesystemdeterminestheaveragevelocity.

Theaveragevelocityisconvertedtoacolor.GenerallyREDtowardthetransducerandBLUEaway.AnatomyofaColorFlowImageTheresultisanimagewithcolorsrepresentingtheaveragevelocities.GeneraldirectionofultrasoundbeamAnatomyofaColorFlowImageTheresultisanimagewithcolorsrepresentingtheaveragevelocities.GeneraldirectionofultrasoundbeamThisareaisblue,soflowisgenerallyawayfromthebeam,lefttorightRABTAnatomyofaColorFlowImageTheresultisanimagewithcolorsrepresentingtheaveragevelocities.GeneraldirectionofultrasoundbeamThisareaisred,soflowisawaythebeam,righttoleftThisareaisblue,soflowisgenerallytowardsfromthebeam,lefttorightRABTDealingwiththeDopplerProblemsWhatisgoingonhere?Whyisthebloodflowmulti-colored,ratherthanallredorallblue?ColorFlowhasDoppler’sLimitationsOfthethreepiecesofinformationfromaDopplersignal,CFMusesonlytheVELOCITYinformation.VelocityIntensityTurbulence

Andhasthesamelimitations:Aliasing:MaximumvelocitylimitedbyPRFDependentonangleofflowFrameRatesareaproblemtoo!SinceColorFlowrequireslotsofDopplersignals,theframeratescanbeslow.

Youronlychoicesare:Dolesscolorflow(makethecolorboxsmaller)CheatL500:ParallelProcessingL400:AutomaticControlTechnologyDealingwiththeDopplerProblemsWhatisgoingonhere?Whereistheflowvelocitythehighest?

A?B?C?ABCDealingwiththeDopplerProblemsTheflowvelocityisthesameinthevessel,buttheanglemakesitlooklikethebloodisacceleratingfromAtoBtoC.Whatisgoingonhere?Whereistheflowvelocitythehighest?

A?B?C?ABCDealingwiththeDopplerProblemsWhatisgoingonhere?Whyisthebloodflowmulti-colored,ratherthanallredorallblue?DealingwiththeDopplerProblemsWhatisgoingonhere?Whyisthebloodflowmulti-colored,ratherthanallredorallblue?It’sacombinationofchanginganglesandaliasing.DealingwiththeDopplerProblemsRememberthis?

WhatifweusedIntensityinsteadofVelocitytomaptheflowinformation?VelocityTurbulenceIntensityDealingwiththeDopplerProblemsVelocityasks“howfastisitgoing?”

Velocityissubjecttoangleproblems.Apparentvelocitychangeswithangle.

Velocityissubjecttoaliasing.DependsonPRF.Intensityasks“how

manyaregoing?”

Intensityisnotsubjecttoangleproblems.Howmanydoesn’tchangewithangle.

Intensityisnotsubjecttoaliasing.Howmanydoesn’tchangewithsamplingrate.DealingwiththeD