Term
The frequency of sound changes when the sound source and the receiver move closer together or further apart. What is this called? |
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Definition
Doppler Shift
Doppler Frequency |
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Term
What is doppler shift used to measure |
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Definition
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Term
As sound approaches a receiver, what seems to happen to its frequency/pitch? |
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Definition
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Term
As sound departs a receiver, what seems to happen to its frequency/pitch? |
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Definition
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Term
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Definition
The process of extracting low doppler frequency from the higher transducer frequency |
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Term
What is the doppler shift range? |
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Definition
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Term
If the transmitted signal is 5,000,000 Hz and the received signal is 5,003,000 Hz, what is the doppler shift? Which direction is the blood moving? |
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Definition
3,000Hz (positive, so...)
Toward Transducer |
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Term
When RBCs move toward the transducer, is the doppler shift negative or positive? |
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Definition
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Term
When RBCs move away from the transducer, is the doppler shift negative or positive? |
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Definition
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Term
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Definition
This is purely a magnitude, indicating the distance traveled |
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Term
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Definition
This is magnitude, indicating the distance traveled, and the direction traveled |
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Term
Speed is reported in what units? |
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Definition
cm/s (any distance divided by time) |
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Term
Doppler provides a (quantitative|qualitative) measurement |
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Definition
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Term
Spectral Doppler (Color Flow) provides a (quantitative|qualitative) measurement |
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Definition
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Term
The ideal transducer angle (angle correction/cosine) for taking doppler measurements is what? |
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Definition
0 - 60 Degrees
(0 or 180 degrees is ideal) |
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Term
What is the relationship between doppler shift and blood flow velocity? |
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Definition
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Term
Why is there a "2" in the doppler shift equation? |
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Definition
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Term
What is the relationship between doppler shift and transducer frequency? |
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Definition
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Term
When blood flow is ___ to the sound beam, the entire doppler shift is measured, making the velocity measurement 100% accurate |
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Definition
Parallel
(0 or 180 Degrees) |
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Term
When blood flow is ___ to the sound beam, the no doppler shift is measured, making the velocity measurement 0% accurate |
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Definition
Perpendicular
(90 Degrees) |
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Term
The % of true velocity that is measured depends on the ___ of the angle between the sound beam and the direction of flow |
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Definition
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Term
A Doppler system that measure the presence of blood flow without distinguishing its direction is called what? |
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Definition
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Term
A ___ doppler shift indicates flow ___ the transducer whereas a ___ doppler shift represents flow ___ the transducer |
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Definition
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Term
A doppler system that measures the presence of blood flow and its direction is called what? |
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Definition
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Term
Nondirectional doppler uses how many speakers? |
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Definition
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Term
Bidirectional doppler uses how many speakers? |
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Definition
2 (one for flow in each direction) |
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Term
When flow toward the transducer is displayed graphically, above the baseline, and flow moving away from the transducer is shown below the baseline, what is this called? |
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Definition
Phase Quadrature
Quadrature Detection |
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Term
When assessing adjacent artery and veins with doppler, how can we determine which is which? |
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Definition
The artery & vein will each be heard from a different speaker. The arterial signal will have a higher velocity. |
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Term
How many crystals are needed for continuous wave doppler? |
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Definition
Two - one for transmitting, one for receiving |
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Term
What is the greatest advantage of continuous wave doppler? |
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Definition
Its ability to accurately measure very high velocities |
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Term
What is the primary disadvantage of continuous wave doppler? |
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Definition
Range Ambiguity - its inability to determine the exact location of the moving RBCs |
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Term
With continuous wave doppler, at which part of the beam are velocities measured? |
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Definition
Velocities are measured along the entire beam |
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Term
Another disadvantage of continuous wave doppler is its lack of ___: doppler shifts from deeper RBCs may be incorrectly interpreted as having been created by ___ RBCs |
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Definition
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Term
Simultaneous anatomic imaging and doppler imaging is called what? |
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Definition
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Term
A transducer which contains only two crystals and no backing material is called what? |
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Definition
Dedicated Continuous Wave
(Pedoff) |
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Term
Which kind of transducer offers these advantages:
- higher sensitivity
- high quality factor
- narrow bandwidth
- undampened signal strength |
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Definition
Dedicated Continuous Wave
(Pedoff) |
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Term
How many crystals are needed for pulsed wave doppler? |
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Definition
One - alternates between transmit & receive |
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Term
With pulsed wave doppler, at which part of the beam are velocities measured? |
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Definition
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Term
What is the greatest advantage of pulsed wave doppler? |
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Definition
Ability to select the exact location to assess
- Range Resolution/Specificity
- Freedom from Range Ambiguity Artifact |
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Term
What is the primary disadvantage of pulsed wave doppler? |
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Definition
Inaccurate measurement of high velocity signals (aliasing) |
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Term
What is it called when high velocity flow in one direction is displayed as traveling in the opposite direction? |
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Definition
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Term
Which kind of transducer offers these advantages:
- low quality factor
- low sensitivity
- wide bandwidth pulses |
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Definition
Pulsed Wave Doppler Transducers |
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Term
Can pulsed wave doppler transducers produce images as well? |
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Definition
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Term
Aliasing only occurs with what type of doppler? |
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Definition
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Term
This is the highest doppler frequency or velocity that can be measured without the appearance of aliasing |
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Definition
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Term
Half the PRF is also called what? |
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Definition
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Term
The Nyquist Limit is measured in what units? |
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Definition
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Term
Deeper sample volumes create more ___ |
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Definition
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Term
The sampling rate of pulsed wave doppler is the ___ |
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Definition
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Term
Will the following result in more or less aliasing?
- slower blood velocity
- lower transducer frequency
- shallow gate |
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Definition
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Term
Will the following result in more or less aliasing?
- faster blood velocity
- higher transducer frequency
- deep gate |
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Definition
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Term
What happens to the PRF/Nyquist Limit when the sample volume gate is shallow? |
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Definition
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Term
What happens to the PRF/Nyquist Limit when the sample volume gate is deep? |
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Definition
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Term
What type of transducers create more aliasing? |
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Definition
High Frequency Transducers |
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Term
What type of transducer is less likely to create doppler shifts that exceed the Nyquist Limit? |
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Definition
Low Frequency Transducers |
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Term
These 5 techniques can be used to avoid what?
1. Adjust scale to maximum
2. Use lower freq transducer
3. Use shallower sample volume gate
4. Use CW Doppler
5. Adjust baseline (appearance only) |
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Definition
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Term
What is an advantage of adjusting doppler scale to its maximum? |
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Definition
Doing so increases PRF & Nyquist Limit to maximum values, thus reducing the chances of aliasing |
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Term
What is a disadvantage of adjusting doppler scale to its maximum? |
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Definition
1. Higher PRF reduces sensitivity to low velocities
2. Aliasing can still occur |
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Term
What is an advantage of selecting a lower frequency transducer? |
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Definition
Lower doppler shifts are less likely to exceed the Nyquist Limit and alias |
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Term
What is a disadvantage of selecting a lower frequency transducer? |
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Definition
Nothing significant, although lower quality grayscale anatomical images can occur during duplex imaging |
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Term
What is an advantage of using a shallower sample volume gate? |
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Definition
The PRF/Nyquist Limit increases, reducing the chances of aliasing |
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Term
What is a disadvantage of using a shallower sample volume gate? |
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Definition
Nothing really, although in some cases the sonographer may be unable to adjust the view to allow for a shallower sample volume gate |
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Term
What is an advantage of using CW doppler? |
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Definition
Aliasing never happens with CW |
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Term
What is a disadvantage of using CW doppler? |
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Definition
Range Ambiguity - the entire beam is measured |
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Term
What is an advantage of using baseline shift? |
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Definition
High velocity flows are displayed in the proper direction. Although no more accurate, it is more pleasing to the eye |
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Term
What is a disadvantage of using baseline shift? |
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Definition
1. Nothing changes other than visual appearance - audio signal will still come from the wrong speaker
2. Aliasing can still occur |
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