超声彩色多普勒colordoppler.ppt

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 Principles Color 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.
• If the flow isn’t parallel to the ultrasound beam, the ultrasound system only see’s a portion of the 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.
Pop Quiz
1. Describe 3 key differences between the two Doppler Waveforms below. 2. Match the waveform with the sample volume position.
1
2
A
B
The Angle Problem
The Aliasing Problem
• What if you checked
your clock every 5
1
seconds... what
would you see on
the second hand?
2
3
4
The Aliasing Problem
• What happens if you
Pop Quiz
• How fast can the clock be, if you’re going to accurately demonstrate it’s direction when you look at it every 15 seconds?
Pop Quiz
• How often do you
have to look at the
12
clock to correctly
determine the
direction of the
6 seconds
Pop Quiz
• How fast can the clock be, if you’re going to accurately demonstrate it’s direction when you look at it every 15 seconds?
The Doppler Equation
v=
• Don’t memorize this.
fd ·c 2 ft cos
• But remember a couple of rules of thumb:
WHAT
– The apparent velocity is dependent on the angle ()
SO WHAT
You won’t get much flow when the angle is near 90°
– The higher the transmit
frequency (ft), the lower the detected velocity
Lower frequency probes are used to measure higher velocities
Doppler Processor
• The vertical position represents the object’s velocity.
Doppler Processor
• When several objects move at the same velocity, the corresponding dot on the spectrum is brighter.
look at the same
11
clock every 55
seconds?
10
9 8
Pop Quiz
• How often do you
have to look at the
12
clock to correctly
determine the
direction of the
second hand?
Doppler Processor
Velocity
Doppler Information
There are 3 key pieces of information in a Doppler signal
Turbulence
Intensity In general, flow toward the transducer will be above the baseline, and flow away from the transducer will be below the baseline.