超声彩色多普勒colordoppl.ppt
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1、Doppler PrinciplesColor PrinciplesThe DifferencesIn Grayscale,strong echo reflections cause pixels to be displayed.In Color and Doppler,changes in frequency cause pixels to be colored.A Doppler ProcessorThe Doppler processor puts a dot on the“spectrum”based on the velocity of a moving object.Doppler
2、 ProcessorWhen there are objects moving at different speeds,the Doppler processor displays a dot for each object.Doppler ProcessorThe vertical position represents the objects velocity.Doppler ProcessorWhen several objects move at the same velocity,the corresponding dot on the spectrum is brighter.Do
3、ppler ProcessorDoppler InformationVelocityTurbulenceIntensityThere are 3 key pieces of information in a Doppler signal In general,flow toward the transducer will be above the baseline,and flowaway from the transducer will be below the baseline.Pop Quiz1.Describe 3 key differences between the two Dop
4、pler Waveforms below.2.Match the waveform with the sample volume position.AB21The Angle ProblemIf the flow isnt parallel to the ultrasound beam,the ultrasound system only sees a portion of the velocity.Actual VelocityApparent VelocityThe Angle ProblemThe transducer only“sees”a portion of the total v
5、elocity.The Angle ProblemOn the other side,the apparent direction appears to be opposite,even though the flow direction is the same!The Angle ProblemAnd in the center.there is NO apparent flow.Doppler processors cannot see flow perpendicular to the ultrasound beam.The Doppler EquationDont memorize t
6、his.But remember a couple of rules of thumb:WHATSO WHATThe apparent velocity is You wont get much flow whendependent on the angle()the angle is near 90The higher the transmit Lower frequency probes are frequency(ft),the lower the used to measure higherdetected velocityvelocitiesv=fd c2 ft cos The Al
7、iasing ProblemWhat if you checked your clock every 5 seconds.what would you see on the second hand?1234The Aliasing ProblemWhat happens if you look at the same clock every 55 seconds?111098Pop QuizHow often do you have to look at the clock to correctly determine the direction of the second hand?12Po
8、p QuizHow often do you have to look at the clock to correctly determine the direction of the second hand?126Every 29.99999 secondsPop QuizHow fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?Pop QuizHow fast can the clock be,if youre g
9、oing to accurately demonstrate its direction when you look at it every 15 seconds?60 sec.clockPop QuizHow fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?60 sec.clock50 sec.clockPop QuizHow fast can the clock be,if youre going to accu
10、rately demonstrate its direction when you look at it every 15 seconds?60 sec.clock50 sec.clock40 sec.clockPop QuizHow fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?60 sec.clock50 sec.clock40 sec.clock30 sec.clock?Pop QuizHow fast ca
11、n the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?No faster than one rotation every 30 seconds.60 sec.clock50 sec.clock40 sec.clock30 sec.clock20 sec.clock?Pop QuizWhat if you looked at the clock every 10 seconds?Pop QuizWhat if you looked at
12、the clock every 10 seconds?No faster than one rotation every 20 seconds.The faster you sample,the faster the clock can be.50 sec.clock40 sec.clock30 sec.clock20 sec.clock15 sec.clock?The Aliasing ProblemPulsed Doppler has the limitation that the maximum velocity is determined by the“sampling rate.”T
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