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66 Cards in this Set
- Front
- Back
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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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Doppler Shift
Doppler Frequency |
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What is doppler shift used to measure
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Velocity of Blood Flow
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As sound approaches a receiver, what seems to happen to its frequency/pitch?
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Increases
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As sound departs a receiver, what seems to happen to its frequency/pitch?
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Decreases
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The process of extracting low doppler frequency from the higher transducer frequency is called what?
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Demodulation
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What is the doppler shift range?
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20Hz - 20,000Hz (20kHz)
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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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3,000Hz (positive, so...)
Toward Transducer |
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When RBCs move toward the transducer, is the doppler shift negative or positive?
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Positive
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When RBCs move away from the transducer, is the doppler shift negative or positive?
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Negative
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This is purely a magnitude, indicating the distance traveled
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Speed
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This is magnitude, indicating the distance traveled, and the direction traveled
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Velocity
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Speed is reported in what units?
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cm/s (any distance divided by time)
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Doppler provides a (quantitative|qualitative) measurement
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Quantitative
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Spectral Doppler (Color Flow) provides a (quantitative|qualitative) measurement
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Qualitative
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The ideal transducer angle (angle correction/cosine) for taking doppler measurements is what?
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0 - 60 Degrees
(0 or 180 degrees is ideal) |
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What is the relationship between doppler shift and blood flow velocity?
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Directly Related
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Why is there a "2" in the doppler shift equation?
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Transmit/Receive Time
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What is the relationship between doppler shift and transducer frequency?
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Directly Related
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When blood flow is ___ to the sound beam, the entire doppler shift is measured, making the velocity measurement 100% accurate
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Parallel
(0 or 180 Degrees) |
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When blood flow is ___ to the sound beam, the no doppler shift is measured, making the velocity measurement 0% accurate
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Perpendicular
(90 Degrees) |
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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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Cosine
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A Doppler system that measure the presence of blood flow without distinguishing its direction is called what?
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Nondirectional Doppler
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A ___ doppler shift indicates flow ___ the transducer whereas a ___ doppler shift represents flow ___ the transducer
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+ / towards
- / away from |
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A doppler system that measures the presence of blood flow and its direction is called what?
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Bidirectional Doppler
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Nondirectional doppler uses how many speakers?
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1
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Bidirectional doppler uses how many speakers?
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2 (one for flow in each direction)
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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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Phase Quadrature
Quadrature Detection |
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When assessing adjacent artery and veins with doppler, how can we determine which is which?
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The artery & vein will each be heard from a different speaker. The arterial signal will have a higher velocity.
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How many crystals are needed for continuous wave doppler?
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Two - one for transmitting, one for receiving
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What is the greatest advantage of continuous wave doppler?
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Its ability to accurately measure very high velocities
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What is the primary disadvantage of continuous wave doppler?
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Range Ambiguity - its inability to determine the exact location of the moving RBCs
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With continuous wave doppler, at which part of the beam are velocities measured?
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Velocities are measured along the entire beam
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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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TGC
Fewer |
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Simultaneous anatomic imaging and doppler imaging is called what?
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Duplex Imaging
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A transducer which contains only two crystals and no backing material is called what?
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Dedicated Continuous Wave
(Pedoff) |
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Which kind of transducer offers these advantages:
- higher sensitivity - high quality factor - narrow bandwidth - undampened signal strength |
Dedicated Continuous Wave
(Pedoff) |
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How many crystals are needed for pulsed wave doppler?
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One - alternates between transmit & receive
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With pulsed wave doppler, at which part of the beam are velocities measured?
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Gate
Sample Volume |
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What is the greatest advantage of pulsed wave doppler?
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Ability to select the exact location to assess
- Range Resolution/Specificity - Freedom from Range Ambiguity Artifact |
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What is the primary disadvantage of pulsed wave doppler?
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Inaccurate measurement of high velocity signals (aliasing)
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What is it called when high velocity flow in one direction is displayed as traveling in the opposite direction?
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Aliasing
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Which kind of transducer offers these advantages:
- low quality factor - low sensitivity - wide bandwidth pulses |
Pulsed Wave Doppler Transducers
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Can pulsed wave doppler transducers produce images as well?
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Yes
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Aliasing only occurs with what type of doppler?
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Pulsed Wave Doppler
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This is the highest doppler frequency or velocity that can be measured without the appearance of aliasing
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Nyquist Limit
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Half the PRF is also called what?
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Nyquist Limit
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The Nyquist Limit is measured in what units?
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Hz
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Deeper sample volumes create more ___
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Aliasing
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The sampling rate of pulsed wave doppler is the ___
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PRF
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Will the following result in more or less aliasing?
- slower blood velocity - lower transducer frequency - shallow gate |
Less Aliasing
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Will the following result in more or less aliasing?
- faster blood velocity - higher transducer frequency - deep gate |
More Aliasing
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What happens to the PRF/Nyquist Limit when the sample volume gate is shallow?
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High PRF/Nyquist Limit
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What happens to the PRF/Nyquist Limit when the sample volume gate is deep?
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Low PRF/Nyquist Limit
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What type of transducers create more aliasing?
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High Frequency Transducers
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What type of transducer is less likely to create doppler shifts that exceed the Nyquist Limit?
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Low Frequency Transducers
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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) |
Aliasing
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What is an advantage of adjusting doppler scale to its maximum?
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Doing so increases PRF & Nyquist Limit to maximum values, thus reducing the chances of aliasing
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What is a disadvantage of adjusting doppler scale to its maximum?
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1. Higher PRF reduces sensitivity to low velocities
2. Aliasing can still occur |
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What is an advantage of selecting a lower frequency transducer?
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Lower doppler shifts are less likely to exceed the Nyquist Limit and alias
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What is a disadvantage of selecting a lower frequency transducer?
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Nothing significant, although lower quality grayscale anatomical images can occur during duplex imaging
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What is an advantage of using a shallower sample volume gate?
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The PRF/Nyquist Limit increases, reducing the chances of aliasing
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What is a disadvantage of using a shallower sample volume gate?
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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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What is an advantage of using CW doppler?
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Aliasing never happens with CW
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What is a disadvantage of using CW doppler?
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Range Ambiguity - the entire beam is measured
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What is an advantage of using baseline shift?
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High velocity flows are displayed in the proper direction. Although no more accurate, it is more pleasing to the eye
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What is a disadvantage of using baseline shift?
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1. Nothing changes other than visual appearance - audio signal will still come from the wrong speaker
2. Aliasing can still occur |
