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24 Cards in this Set
- Front
- Back
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The Doppler effect is presented as a ____ when the source and the receiver are_____
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Frequency shift, in motion relative to each other
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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 at 10 miles/hour. The Doppler shift is (pos/neg?)
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The Doppler shift is negative because the source and receiver are moving farther apart
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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 (pos/neg ?)
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The Doppler shift is negative because the source and receiver are moving farther apart
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Doppler shift produces information about
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Velocity
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At what angle between the sound beam and the direction of motion will the Doppler shift be the highest?
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0 degree or 180 degree
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At what angle between the sound beam and the direction of motion will the Doppler shift be closest to zero?
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90 degrees. No Doppler frequency exists because the cosine of 90 degree is zero
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What is the difference between speed and velocity?
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Speed has only a magnitude. Velocity has magnitude and direction
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What is the current method of processing Doppler signals?
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The FFT method of spectral analysis is used for pulse and CW. Autocorrelation is the method of spectral analysis for color flow Doppler
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What is the typical range of Doppler shift found in diagnostic imaging examinations?
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Between 20 Hz and 20 kHz (in the audible range)
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The phenomenon where high velocities appear in the opposite direction is called
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Aliasing
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The frequency at which aliasing occurs is called
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Nyquist limit
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The area of interrogation in a pulsed Doppler exam is call
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Sample volume
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True or false. The higher the emitted frequency, the more likely a pulsed wave signal is to alias
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true
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True or false. Shallower sample volume result in more aliasing
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false
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True or false. Only pulsed wave Doppler exams have a sample volume
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true
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An 8 MHz transducer with a pulse repetition frequency of 5,000 Hz is imaging to a depth of 7 cm. What is the Nyquist frequency?
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2.2 kHz (the actual nyquist limit is 1/2 of PRF, 2.5 kHz or 2,500 Hz)
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An 8 MHz transducer with a pulse repetition frequency of 5,000 Hz measures a Doppler shift of 7 kHz. The study is repeated with a 4 MHz transducer. What Doppler shift will be measured?
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3500 Hz
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True or false. A sucessful Doppler exam cannot be performed on a severely anemic patient
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false
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Which technique is used to perform spectral analysis on color Doppler data?
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Autocorrelation
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Which technique is used to perform spectral analysis on pulse Doppler data
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FFT
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Which of the following terms is synonymous with spectral broadening?
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Turbulent flow
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Which of the following is an advantage of a large packet size?
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Increased Doppler accuracy
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Why are dedicated continuous wave Doppler transducers so sensitive?
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Absence of backing material
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True or false. The lumen of a horizontal vessel evaluated with a color Doppler, sector shaped image contains a single color
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False. The vessel will have both the toward and away colors. The center of the lumen will be black
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