超声彩色多普勒colordoppl.ppt

Doppler PrinciplesColor Principles,The Differences,In Grayscale,strong echo reflections cause pixels to be displayed.In Color and Doppler,changes in frequency cause pixels to be colored.,A Doppler Processor,The Doppler processor puts a dot on the“spectrum”based on the velocity of a moving object.,Doppler Processor,When there are objects moving at different speeds,the Doppler processor displays a dot for each object.,Doppler Processor,The vertical position represents the objects velocity.,Doppler Processor,When several objects move at the same velocity,the corresponding dot on the spectrum is brighter.,Doppler Processor,Doppler Information,Velocity,Turbulence,Intensity,There 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 Quiz,1.Describe 3 key differences between the two Doppler Waveforms below.2.Match the waveform with the sample volume position.,A,B,The Angle Problem,If the flow isnt parallel to the ultrasound beam,the ultrasound system only sees a portion of the velocity.,Actual Velocity,Apparent Velocity,The Angle Problem,The transducer only“sees”a portion of the total velocity.,The Angle Problem,On the other side,the apparent direction appears to be opposite,even though the flow direction is the same!,The Angle Problem,And in the center.there is NO apparent flow.Doppler processors cannot see flow perpendicular to the ultrasound beam.,The Doppler Equation,Dont memorize this.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 velocityvelocities,v=,fd c,2 ft cos,The Aliasing Problem,What if you checked your clock every 5 seconds.what would you see on the second hand?,1,2,3,4,The Aliasing Problem,What happens if you look at the same clock every 55 seconds?,Pop Quiz,How often do you have to look at the clock to correctly determine the direction of the second hand?,12,Pop Quiz,How often do you have to look at the clock to correctly determine the direction of the second hand?,12,6,Every 29.99999 seconds,Pop Quiz,How fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?,Pop Quiz,How fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?,60 sec.clock,Pop Quiz,How fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?,60 sec.clock,50 sec.clock,Pop Quiz,How fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?,60 sec.clock,50 sec.clock,40 sec.clock,Pop Quiz,How fast can the clock be,if youre going to accurately demonstrate its direction when you look at it every 15 seconds?,60 sec.clock,50 sec.clock,40 sec.clock,30 sec.clock,?,Pop Quiz,How fast can 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.clock,50 sec.clock,40 sec.clock,30 sec.clock,20 sec.clock,?,Pop Quiz,What if you looked at the clock every 10 seconds?,Pop Quiz,What if you looked at 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.clock,40 sec.clock,30 sec.clock,20 sec.clock,15 sec.clock,?,The Aliasing Problem,Pulsed Doppler has the limitation that the maximum velocity is determined by the“sampling rate.”The sampling rate is known as the PRF,pulse repetition frequency.If the velocity is too high,the flow will appear to go backwards,just like the clock.,Doppler Summary,Three Key Pieces of Information in a Doppler SignalVelocityIntensityTurbulenceIn general,flow toward the transducer is above the baseline,flow away is below the baseline.Major limitation is maximum velocity,which is based on frequency and sampling rate.2nd limitation is the angle of flow relative to the transducer.,Color Doppler,Color Doppler uses the same principals.The system acquires a Doppler Spectrum from many points in the image.For each point,the system determines the average velocity.The average velocity is converted to a color.Generally RED toward the transducer and BLUE away.,Anatomy of a Color Flow Image,The result is an image with colors representing the average velocities.,General directionof ultrasound beam,Anatomy of a Color Flow Image,The result is an image with colors representing the average velocities.,General directionof ultrasound beam,This area is blue,soflow is generally awayfrom the beam,left to right,RABT,Anatomy of a Color Flow Image,The result is an image with colors representing the average velocities.,General directionof ultrasound beam,This area is red,so flow is away the beam,right to left,This area is blue,soflow is generally towardsfrom the beam,left to right,RABT,Dealing with the Doppler Problems,What is going on here?Why is the blood flow multi-colored,rather than all red or all blue?,Color Flow has Dopplers Limitations,Of the three pieces of information from a Doppler signal,CFM uses only the VELOCITY information.VelocityIntensityTurbulenceAnd has the same limitations:Aliasing:Maximum velocity limited by PRFDependent on angle of flow,Frame Rates are a problem too!,Since Color Flow requires lots of Doppler signals,the frame rates can be slow.Your only choices are:Do less color flow(make the color box smaller)CheatL500:Parallel ProcessingL400:Automatic Control Technology,Dealing with the Doppler Problems,What is going on here?Where is the flow velocity the highest?A?B?C?,A,B,C,Dealing with the Doppler Problems,The flow velocity is the same in the vessel,but the angle makesit look like the blood is accelerating from A to B to C.,What is going on here?Where is the flow velocity the highest?A?B?C?,A,B,C,Dealing with the Doppler Problems,What is going on here?Why is the blood flow multi-colored,rather than all red or all blue?,Dealing with the Doppler Problems,What is going on here?Why is the blood flow multi-colored,rather than all red or all blue?,Its a combination of changing angles and aliasing.,Dealing with the Doppler Problems,Remember this?What if we used Intensity instead of Velocity to map the flow information?,Dealing with the Doppler Problems,Velocity asks“how fast is it going?”Velocity is subject to angle problems.Apparent velocity changes with angle.Velocity is subject to aliasing.Depends on PRF.,Intensity asks“how many are going?”Intensity is not subject to angle problems.How many doesnt change with angle.Intensity is not subject to aliasing.How many doesnt change with sampling rate.,Dealing with the Doppler Problems,The result is color flow that is not angle dependent,and not subject to aliasing.We call it Power Doppler Imaging(PDI).It appears to be more sensitive(no zero angle to worry about).,Summary,Doppler provides 3 key types of informationVelocityIntensityTurbulenceVelocity information is subject to angle and aliasing problems.Color Doppler maps average velocity to a color,so it has aliasing and angle problems too.Power Doppler maps intensity to a color,so it does not have aliasing nor angle problems.Frame Rate will be a problem for CFM&PDI unless you have a smart color processor.,