Continuous wave has ____ but no _____ and no ______
continuous wave has range ambiguity but no range specificity and no sample volume
What is an advantage that continuous wave have when considering doppler?
no aliasing
what are the two ways returning waves are processed?
demodulation: by which the doppler shifted frequency change is extracted from the transmit frequency
quadrature phase detector: detects if the frequency is increased or decreased determining the direction.
during continous wave digital processing what does it use to analyze the information?
Fast fourier transfer (FFT): analyzes and displayes all frequencies moving through the sample area.
-X axis: time, Y axis: frequencies
-more accurate
-better sensitivity, less noise
-commonly used in duplex
what is the advantages of using pulsed wave when considering doppler?
has range specificity, sample volume, and range resolution
-we can determine the depth of the returning signal along the scan line
what is the use of a sample volume/sample gate?
samples a specific area
what is the disadvantage of using a larger sample volume?
produces spectral broadening, which is no good
what does pulsed wave use to process frequencies?
fast fourier transfer (FFT)
where do you want to place your sample volume for the best flow?
in the center of the vessel if aliasing isn’t present
when using spectral and color doppler what controls seeing low velocities when using a low PRF?
wall filter
where are lower velocity flow seen?
closer to the vessel wall
what filters or “rejects” low-level signals? and why is it used?
low pass filter/wall filter and it is used to reduce noise in the spectral waveform and allows filtering of low-level doppler shifts
what dopplers are able to use wall filter?
spectral waveform and color doppler
what happens when the PRF is set too high or too low?
too high: display doesn’t display flow adequately
too low: the display will alias
what happens in spectral display if the gain is set too low?
the waveform is difficult to see
it’ll be gray almost black
what happens in spectral display if the gain is set too high?
it’ll add in extra noise and the velocity will be overstimulated, it’ll be very bright, too white
what does color doppler use pulsed ultrasound and multiple gates to detect?
mean velocity in the color box or field of view
what kind of image is color doppler using?
2D image
what is color doppler used for?
to detect the presence of flow and its direction
what is the field of view considered in color doppler?
the box that color doppler is written in
what transducer allows the sonographer to steer the box to change the angle that the sound beam interacts with flow?
linear transducers
what does sector and curvilinear probes use for angling?
they have baked-in angling, but need more manual manipulation to get good angles of less than 60 degrees
what is needed to measure velocity accurately?
multiple ultrasound pulses
what is packet or ensemble length?
group of pulses
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Doppler44
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Optimizing doppler images22
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Imaging processing & display53
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Doppler shift*15
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Inspiration vs Expiration venous blood flow6
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Apply doppler48
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Lateral resolution*11
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Coded excitation*5
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Wall filter8
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Ergonomics6
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Dynamic range8
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Temporal resolution*16
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Artifacts25
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Mock 466
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Mock 363
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Mock 236
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Pulse repetition frequency*15
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Duty factor *7
