超声彩色多普勒colordoppl

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1、DopplerPrinciplesColorPrinciplesTheDifferencesInGrayscale,strongechoreflectionscausepixelstobedisplayed.InColorandDoppler,changesinfrequencycausepixelstobecolored.ADopplerProcessorTheDopplerprocessorputsadotonthe“spectrum”basedonthevelocityofamovingobject.DopplerProcessorWhentherea

2、reobjectsmovingatdifferentspeeds,theDopplerprocessordisplaysadotforeachobject.DopplerProcessorTheverticalpositionrepresentstheobject’svelocity.DopplerProcessorWhenseveralobjectsmoveatthesamevelocity,thecorrespondingdotonthespectrumisbrighter.DopplerProcessorDopplerInformationVeloci

3、tyTurbulenceIntensityThereare3keypiecesofinformationinaDopplersignalIngeneral,flowtowardthetransducerwillbeabovethebaseline,andflowawayfromthetransducerwillbebelowthebaseline.PopQuiz1.Describe3keydifferencesbetweenthetwoDopplerWaveformsbelow.2.Matchthewaveformwiththesamplevolumepos

4、ition.AB21TheAngleProblemIftheflowisn’tparalleltotheultrasoundbeam,theultrasoundsystemonlysee’saportionofthevelocity.ActualVelocityApparentVelocityTheAngleProblemThetransduceronly“sees”aportionofthetotalvelocity.TheAngleProblemOntheotherside,theapparentdirectionappearstobeopposite,

5、eventhoughtheflowdirectionisthesame!TheAngleProblemAndinthecenter...thereisNOapparentflow.Dopplerprocessorscannotseeflowperpendiculartotheultrasoundbeam.TheDopplerEquationDon’tmemorizethis.Butrememberacoupleofrulesofthumb:WHATSOWHATTheapparentvelocityisYouwon’tgetmuchflowwhendepen

6、dentontheangle()theangleisnear90°ThehigherthetransmitLowerfrequencyprobesarefrequency(ft),thelowertheusedtomeasurehigherdetectedvelocityvelocitiesv=fd·c2ftcosTheAliasingProblemWhatifyoucheckedyourclockevery5seconds...whatwouldyouseeonthesecondhand?1234TheAliasingProblemWhathapp

7、ensifyoulookatthesameclockevery55seconds?111098PopQuizHowoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?12PopQuizHowoftendoyouhavetolookattheclocktocorrectlydeterminethedirectionofthesecondhand?126Every29.99999secondsPopQuizHowfastcantheclockbe,ifyou’

8、regoingtoaccuratelydemonst