Ch. 19 Doppler Flashcards
_________________________________ is the change in frequency of sound as the sound source and receiver move closer together or farther apart
Doppler Shift is the change in frequency of sound as the sound source and receiver move closer together or farther apart
Doppler Shift is also called Doppler _______________________
Doppler Shift is also called Doppler Frequency
Doppler Shift is a _____________ frequency that rides on top of the much higher transducer frequency
Doppler Shift is a low frequency that rides on top of the much higher transducer frequency
_________________________ is the process of extracting the low doppler frequency from the transducer’s carrier frequency
Demodulation is the process of extracting the low doppler frequency from the transducer’s carrier frequency
Short formula for Doppler Shift:
Doppler Shift (Hz) = reflected frequency - transmitted frequency
When the doppler shift is positive, the reflected sound has a __________________ frequency than the transmitted sound.
When the doppler shift is positive, the reflected sound has a higher frequency than the transmitted sound
When the doppler shift is negative, the reflected sound has a ____________________ frequency than the transmitted sound.
When the doppler shift is negative, the reflected sound has a lower frequency than the transmitted sound.
Doppler frequencies indicate _________________________, not speed.
Doppler frequencies indicate velocity, not speed
Speed is purely a ____________________________
Speed if purely a magnitude
Velocity is defined by a _______________ and a _________________
Velocity is defined by a magnitude and a direction
long formula for doppler shift:
Doppler Shift = 2 V Fo Cos / C
doppler shift is ____________________ related to the velocity of red blood cells
directly
The faster the velocity, the _____________________ the doppler shift
The faster the velocity, the greater the doppler shift
The x-axis of a doppler spectrum represents _______________
The x-axis of a doppler spectrum represents time
The y-axis of a doppler spectrum represents _________________________ or __________________________
The y-axis of a doppler spectrum represents Doppler shift or velocity
doppler shift is _________________ related to the frequency of the transmitted sound
doppler shift is directly related to the frequency of the transmitted sound
If the transducer frequency is doubled, the doppler shift will _______________
double
What is the range of frequencies for doppler shift?
20 Hertz - 20,000 Hertz (audiable range)
What is the relationship between the transmitted frequency and the doppler shift?
Directly related
When blood cells are moving __________ to the sound beam the entire velocity is measured
When blood cells are moving parallel to the sound beam the entire velocity is measured
The percentage of the true velocity that is measured depends on the ______________ of the angle between the sound beam and the direction of motion.
The percentage of the true velocity that is measured depends on the cosine of the angle between the sound beam and the direction of motion
What information does doppler provide (4 things)?
- presence of flow
- direction of flow
- speed of flow
- characteristics of flow (laminar, turbulent)
cosine of 90 degrees
0%
cosine of 60 degrees
0.5 or 50%
cosine of 0 degrees
100%
cosine of 180 degrees
- 1.0
The most common clinical doppler devices are _______________________________, which distinguish the direction of flow toward or away from the transducer
The most common clinical doppler devices are Bidirectional, which distinguish the direction of flow toward or away from the transducer
Are arterial velocities higher/lower than venous velocities
higher
Continuous wave doppler requires __________ crystals within the transducer
Continuous wave doppler requires 2 crystals within the transducer
What is the greatest advantage of continuous wave doppler?
Accurately measure very high velocities
Primary disadvantage of continuous wave doppler is?
The exact location of the moving blood cells cannot be determined
The limitation of continuous wave doppler is that the exact location of moving blood cells cannot be determined and this is called:
range ambiguity
Another disadvantage of continuous wave doppler is its lack of:
TGC’s time gain compensation
A dedicated continuous wave transducer is simple because it does not create __________________________________
A dedicated continuous wave transducer is simple because it does not create anatomic images
Dedicated continuous wave transducers contain _____ elements, each shaped like a ___________________
Dedicated continuous wave transducers contain 2 elements, and each shaped like a semicircle
Simultaneous imaging and doppler imaging is called:
Duplex imaging
Dedicated continuous wave transducers do not use ______________________ which results in:
- undampened transmitted signal
- narrow bandwidth
- high quality factor
- higher sensitivity
Dedicated continuous wave transducers do not use backing which results in:
- undampened transmitted signal
- narrow bandwidth
- high quality factor
- higher sensitivity
In Pulsed wave doppler how many PZT crystals are necessary?
1
What is the greatest advantage of pulsed wave doppler?
the greatest advantage of pulsed wave doppler is being able to select the exact location where velocities are measured, called range resolution
The greatest advantage of pulsed wave doppler is called:
Range Resolution, Range Specificity, or freedom from range ambiguity artifact
With pulsed wave doppler the sonographer positions a small marker called the _______________________________________ on a 2D image
With pulsed wave doppler the sonographer positions a small marker called the sample volume or sample gate on a 2D image
What is the primary disadvantage of pulsed wave doppler?
Inaccurate measurement of high velocity signals
When high velocity flow is incorrectly displayed as traveling in the opposite direction the inaccuracy is called _______________________
When high velocity is incorrectly displayed as traveling in the opposite direction the inaccuracy is called Aliasing
Pulse wave doppler transducers are imaging transducers and contain _________________________________, which provide low Q-factor, lower sensitivity, and wide bandwidth pulses.
Pulse wave doppler transducers are imaging transducers and contain backing material, which provide low Q-factor, lower sensitivity, and wide bandwidth pulses.
_______________________ is the most common error associated with doppler ultrasound.
Aliasing is the most common error associated with doppler ultrasound
An alias is a:
false identity
Aliasing occurs only with __________________ doppler
Aliasing occurs only with pulsed doppler
Nyquist limit equation
Nyquist limit = PRF/2
______________________________ is the highest doppler frequency that can be measured without appearance of aliasing
Nyquist limit is the highest doppler frequency that can be measured without appearance of aliasing
2 ways to avoid aliasing are:
- raise the nyquist limit
- reduce the doppler shift
The sampling rate of pulsed doppler is the systems _____________
The sampling rate of pulsed doppler is the systems PRF
When sample volume is deep the PRF Is ___ and the nyquist limit is ___
low, low
Since deeper sample volumes have a lower PRF, __________ happens
Aliasing
Higher or Lower frequency transducers create more aliasing
Higher
5 techniques used to avoid aliasing artifact
- adjust scale to max
- select new ultrasonic view with shallower sample volume
- select lower frequency transducers
- use baseline shift
- use continuous wave doppler
When the sonographer adjusts the scale to its max the ________________ is also increased to its max
When the sonographer adjusts the scale to its max the PRF is also increased to its max
What is the advantage of maximizing the PRF?
Maximizing the PRF, raises the nyquist limit and aliasing is less likely to occur
What is the disadvantage of raising the PRF to its max?
reduces sensitivity to low velocities
What is the advantage of selecting a lower frequency transducer?
lower shifts occur with lower frequency transducers
Advantage of zero baseline shift
High velocity flows are displayed in proper direction
Advantage of using continuous wave doppler
Aliasing never appears with continuous wave doppler
Eliminating aliasing improves the ability to measure the ____________________________ with doppler
Eliminating aliasing improves the ability to measure the maximum velocity with doppler
Gray shades on a Doppler spectrum are related to the ______________________ of reflected signal, or the number of ____________________________ creating the reflection.
Gray shades on a Doppler spectrum are related to the amplitude of reflected signal, or the number of blood cells creating the reflection.
_______________________________ is a form of 2D doppler where velocity information is coded into colors and superimposed on a 2 dimensional gray scale anatomic image
Color Flow Doppler is a form of 2D doppler where velocity information is coded into colors and superimposed on a 2 dimensional gray scale anatomic image
Color doppler provides information on the location of flow and therefore:
- is a pulsed ultrasound technique
- has range resolution
- is subject to aliasing
Color Doppler measures the ____ velocity.
Color Doppler measures the mean velocity
Spectral Doppler measures the _______________ velocity
Spectral Doppler measures the peak velocity
Color doppler uses a “dictionary” or a ___________________________ to concert measured velocities into colors that appear on the image
Color doppler uses a “dictionary” or a lookup table to concert measured velocities into colors that appear on the image
The two most commonly used dictionaries for color doppler are called:
Velocity mode and Variance mode
What do the colors mean in a velocity mode map mean?
Flow direction and velocity
What do the colors mean on a variance mode map?
In addition to direction and velocity, variance mode distinguishes laminar flow from turbulent flow
with the variance map, remember that the left side is always the __________________ side
with the variance map, remember that the left side is always the laminar side
The black region in the middle of the color map means?
No doppler shift
With color doppler multiple ultrasound pulses are used to accurately determine blood velocities, these multiple pulses are called a
packet or ensemble
Power mode only identifies the presence of a
Doppler shift
Power mode is _____________________ color doppler
Power mode is non-directional color doppler
Power Doppler is also known as:
~ energy mode
~ color angio
In power mode the ____________ of the reflected signal is processed without regard to the bloods direction or speed
In power mode the strength of the reflected signal is processed without regard to the bloods direction or speed
The amplitude of the reflection is _____________________ related to the number of moving blood cells
The amplitude of the reflection is directly related to the number of moving blood cells
3 advantages of power mode are:
- Increased sensitivity
- unaffected by doppler angles
- no aliasing
3 disadvantages of power mode are:
- no measurement of velocity or direction
- lower frame rates
- susceptible to motion of the transducer, patient, or soft tissues, which may result in a burst of color, or flash artifact
On spectral displays, the low frequency doppler shift artifacts are called _________________________
On spectral displays, the low frequency doppler shift artfiacts are called clutter
With color doppler, the low frequency doppler shifts are called ______________________________________
with color doppler, the low frequency doppler shifts are called Ghosting Artifact
What is used to eliminate low frequency doppler shifts from moving anatomy rather than from moving blood cells?
Wall filter
Wall Filters serve as a _____________________ for doppler
Wall Filters serve as a Reject for doppler
With color Doppler, _____________________ eliminate color arising from slow velocity reflectors
With color doppler, wall filters eliminate color arising from slow velocity reflectors
___________________________ is a special form of “mirror image” artifact that arises only with spectral doppler
Crosstalk is a special form of “mirror image” artfiact that arises only with spectral doppler
Crosstalk results from either:
- Doppler gain is too high
- incident angle is near 90°
_______________________________________ is a tool that breaks the complex signal into its basic “building blocks” and identifies the individual velocities that make up the reflected doppler signal.
Spectral analysis is a tool that breaks the complex signal into its basic “building blocks” and identifies the individual velocities that make up the reflected doppler signal
2 methods of spectral analysis are:
- Fast Fourier Transform (FFT)
- Autocorrelation
_____________________________________ is a digital (computer-based) technique that is used to process both pulsed and continuous wave doppler signals
Fast Fourier Transformation is a digital (computer-based) technique that is used to process both pulsed and continuous wave doppler signals
Fast Fourier Transformation has what 2 advantages?
- exceedingly accurate
- displays all individual velocities
The spectral display of an FFT distinguishes _______________________ flow from __________________________ flow
The spectral display of an FFT distinguishes laminar flow from turbulent flow
With laminar flow the region between the baseline and the spectrum that is “clear” and is called the
spectral window
With turbulence flow the spectral window is filled in and is known as
spectral broadening
The digital technique used to analyze color flow doppler is called ________________________________
The digital technique used to analyze color flow doppler is called Autocorrelation
Autocorrelation is somewhat less accurate but substantially faster to perform than ________________________________
Autocorrelation is somewhat less accurate but substantially faster to perform than Fast Fourier Transformation
The Doppler effect is presented as a ___________________ when the source and receiver are ________________
The Doppler effect is presented as a frequency shift when the source and receiver are in motion relative to each other
Starting from the same point, the sound source is moving toward the east at 12 miles/hour and the receiver is moving toward the west 10 miles/hour. The Doppler shift is ____________________ (positive or negative)
The Doppler shift is negative because the source and receiver are moving farther apart
Starting from the same point, the receiver is moving toward the west at 12 miles/hour and the source is moving toward the west at 10 miles/hour. The Doppler shift is _______________________ (positive or negative)
The Doppler shift is negative because the source and receiver are moving farther apart
