超声彩色多普勒
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• 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 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 ()
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?
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?
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
Pop Quiz
• How often do you
have to look at the
12
clock to correctly
determine the
direction of the
6
second hand?
Every 29.99999 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?
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 Байду номын сангаасisplays a dot for each object.
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.
The Differences
• In Grayscale, strong echo reflections cause pixels to be displayed.
• In Color and Doppler, changes in frequency cause pixels to be colored.
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
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.
Apparent Velocity
The Angle Problem
• The transducer only “sees” a portion of the total velocity.
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 ()
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?
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?
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
Pop Quiz
• How often do you
have to look at the
12
clock to correctly
determine the
direction of the
6
second hand?
Every 29.99999 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?
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 Байду номын сангаасisplays a dot for each object.
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.
The Differences
• In Grayscale, strong echo reflections cause pixels to be displayed.
• In Color and Doppler, changes in frequency cause pixels to be colored.
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
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.