Ch19 Doppler Flashcards
Doppler shift is also called
Doppler frequency
When blood cells move toward the transducer
Positive Doppler shift
What does the “2” in the Doppler equation represent
It accounts for transmission and reflection
What is the definition of speed?
Distance per time
What is the definition of velocity?
Distance per time AND direction
Doppler shift are velocities. They give us a speed and a direction
Which cos angel is accepted
60°
What is Doppler shift directly related to?
blood cell velocity
transducer frequency
cos
What is the equation for velocity?
Velocity(cm/s) = Doppler shift (khz) * propagation speed(cm/s)
—————————————————
2* transmitted frequency (Khz) * cos
X-axis of Doppler spectrum
Time
Away from the transducer =
Negative Doppler shift
Y-axis of Doppler spectrum =
Velocity
T or F
Perpendicular angle is the best Doppler measurement
False
Parallel is the best but not achievable
What angle do you want to be at?
60 °
What is the most common error in Doppler US
Aliasing
When there is an angle between the directions of the sound beam and the flow, what happens?
Doppler measures something less than the true velocity
What is the equation for measured velocity?
true velocity x cos
Displaying flow Below the baseline means
Flow away from the transducer
Which Doppler uses two crystals
Continuous wave Doppler
How many crystals does the pulsed wave Doppler have
1
What is the primary disadvantage of CW
Range ambiguity
T or F? Does pulsed wave have one crystal?
True
What is other disadvantage of CW Doppler
No TGC display
What is the definition of range ambiguity?
Sonographer will not know exactly where the sound is coming from
Advantages of CW Doppler
-Does not produce aliasing
-Ability to detect very high velocities
What does triplex imaging includes
Anatomical image
Tracing
Color Doppler
Which has good range resolution
PW or CW
PW
What are the advantages of Pulsed Wave?
Range Resoultion
Sample Volume
gray shades on a doppler spectrum are related to
amplitude of the reflected signal
or
number of blood cells creating the reflection
What is the definition of range resolution
Being able to select the exact location where velocities are measured
What is the sample volume (gate)
Depending on where the gate is placed and the size of it will depend on the appearance of the spectral tracing
Where do you receive the most accurate information?
Place gate in valve jet (center of blood vessel) which is the fastest portion of the blood vessel
T or F? Centering and narrowing the gate will produce a clean and clear tracing
True
anything above the nyquist limit is
Aliasing
How does transducer frequency affect aliasing ?
Higher frequency create more aliasing
Less aliasing
slower blood velocity
lower frequency transducer
shallow gate (high PRF)
More aliasing
faster blood velocity
higher frequency transducer
deep gate (low PRF)
What is the equation of Nyquist limit?
PRF
——-
2
Does aliasing occur with CW Doppler
NO
What is the Nyquist limit?
the highest doppler frequency or velocity that can be measured without the appearance of aliasing
Increasing PRF raises the nyquist limit and reduces
Aliasing
Five techniques to avoid aliasing?
-Adjust scale
-Lower frequency transducer
-Use CW Doppler
-Use baseline shift
-Select new, shallow view
Eliminating aliasing ______ the ability to measure the maximum velocity with Doppler
improve
The black region in the middle of the color map indicates?
No Doppler shift
Color Doppler provides information on the location of flow and therefore:
is a pulsed ultrasound technique
has range resolution
is subject to aliasing
T or F
When multiple colors appear, Colors near the black line is slower velocity
True
Color doppler reports what
average or mean velocities
Pulsed and Continuous (spectral) measures what
peak velocity
What information does the variance mode show
Laminar flow
Turbulent flow
In variance mode, left =
Laminar flow
smaller less packet
less accurate doppler
less sensitive to slow velocity or low flow
higher frame rate; improved temporal resolution
large packet
more accurate doppler
more sensitive to fast velocity or flow
lower frame rate, degraded temporal resolution
Power mode is
non directional color doppler
In variance mode,
Right=
Turbulent flow
in power doppler image
all vessels have the same color, regardless of the direction of blood flow
False echos that appears on our image are
Artifacts
Energy mode or color angio is also
Power Doppler
three advantages of power mode
increased sensitivity to low flow or velocity
unaffected by doppler angles unless the angle is 90
no aliasing
T or F
Color power Doppler is non-directional
True
Eliminating low frequency Doppler signal near the spectral baseline is
Wall filter
three disadvantages of power mode
no measurement of velocity or direction
lower frame rates (reduced temp resoultion)
susceptible to motion of the transducer, pt, soft tissues which may result in a burst of color, or flash artifact
Wall filter eliminates what Doppler shift artifacts
Clutter
Ghosting
What is the form of mirror image artifact that appears on the spectral display?
Crosstalk
