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88 Cards in this Set
- Front
- Back
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the doppler effect occurs
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all echoes from moving sources
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the doppler effect depends on
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the closing velocity between transducer and tissue, carrier frequency, and u/s propagation velocity
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the shape of the sample volume in PW Doppler has a large effect on the content of the doppler signal
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true
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to measure flow velocity with color flow imaging
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a sample volume is placed in the faster streamline and set at angle correction parallel to vessel wall
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To form the color flow image, the system samples down each Doppler image scan line for
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The average Doppler shift frequency
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Separating moving soft tissues from moving blood in a color flow image test for
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The relationship between amplitudes and frequencies of the Doppler signal
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The smallest vessels that appear in a color flow image are about 1 mm diameter. The smaller vessels are absent because
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Small vessels do not reflect as well as larger vessels do
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Detecting color flow depends on
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Changes in echo signal phase
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Power Doppler imaging is a good choice for
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Showing blood perfusion through the tissue
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Power Doppler is limited because
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It does not show direction of flow
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Turbulance in color flow vascular imaging appears as
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A mottled pattern of color or mottled pattern of red and blue with changing saturation
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Color flow imaging in the vascular system usually uses
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A linear sequence array transducer
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What is the maximum velocity limit for a 3 megahertz continuous wave Doppler image at 4 cm deep
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CW has no maximum limit
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Aliasing occurs when the frequency shift exceed
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1/2 the PRF
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When imaging the portal vein in the liver and no color is detected in the vein, what can you do to improve the sensitivity of flow
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Decrease PRF (for slow flow)
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The packet size ( or ensemble length) in color Doppler refers to the number of
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Pulses per scan line
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If the Doppler angle of incidence is underestimated, what error will result?
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Velocity estimate will be inaccurate
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The processing technique for determining direction in CW Doppler is
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Fast Fourier Transform
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What method is used to steer the color box?
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Electronic time delays
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If the frequency of the returning echo is higher than the fundamental transmitted frequency, which will occur?
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Positive shift with red color
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The Doppler spectral display shows
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Relative signal power at each frequency in the Doppler signal
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If you increase the wall filter during Doppler sampling, it will
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Reduce display of low-frequency shift
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What technique is used to perform the spectral analysis?
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Fast fourier transform
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If you increase the transmit frequency of the color Doppler, what will happen?
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Improved sensitivity to slow flow
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If you lower the color threshold, what will occur?
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Increased color fill within the vessel
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The Doppler frequency shift is defined as
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The difference between transmitted and received frequencies
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From the Doppler equation, which would not be true?
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Increasing Doppler frequency will incase frequency shift
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what does brightness of the z axis on the Doppler spectrum refer to?
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Amplitude
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The Nyquist limit refers to
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Sampling frequency required for Doppler samples without aliasing
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What can you adjust to improve the frame rate?
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Decrease size of color box and decreased scan line density
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What adjustments can you make to decrease aliasing?
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Increase PRF
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With the following scan parameters, what is the frequency at which aliasing will occur? 5MHz fundamental frequency, 3 kHz PRF, 4 cm depth, 1.5 mm sample volume width.
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3 kHz ( Nyquist limit is 1/2 PRF)
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The faster techniques used to obtain the mean Doppler frequency in color flow is
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Autocorrelation
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If you see spectral broadening in the spectral analysis display, it usually means
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Turbulent flow
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Which of the following refer to the number of pulses used to measure the velocity along one scan line?
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Packet size or ensemble length
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Which analysis method would show turbulance with color Doppler?
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variance mode color display
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Which term refers to the axial length of the sample volume
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Color gate
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Spectral analysis is used for
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Showing the distribution and magnitude of frequency shift in the Doppler signal
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what adjustments can you make to eliminate color flash artifact?
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increase wall filter
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Which of the following is not true for turbulent flow?
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causes increase in pressure downstream
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Which conditions are most likely to produce turbulance?
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5 mm diameter with 300 cm / sec velocity (Reynolds number =average speed x diameter x density)
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Which of the following are true regarding color Doppler images?
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Color image is superimposed over the B mode image
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Which of the following will decrease frame rate?
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Increasing line density
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When using duplex scanning, how many pulses per scan line are usually used to create the gray scale image?
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1 - 2
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If you increase the packet size, what will result?
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Decreased frame rate
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Which controls on the control panel adjusts Doppler PRF?
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Spectral velocity scale
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When you increase the Doppler frequency, what occurs?
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Increased Doppler frequency shift
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What should you adjust to improve color Doppler sensitivity to flow?
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Lower wall filter settings
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If you lower the PRF, which of the follow occurs?
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Nyquist limit is decreased
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What part of the Doppler spectrum in color -encoded with color Doppler
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The frequency shift
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What color would represent flow at 90 degrees to the sound beam?
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Black
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What color is usually represented as moving for the transducer?
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Red
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Why does the frame rate decrease when adding color to the grayscale image?
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More pulses are required for each scan line
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Which control determines the grayscale brightness at which color will display instead of grayscale?
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Priority
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With reference to the Doppler equation, the frequency shift will increase by increasing the
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Transmit frequency
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What effects the spatial resolution of the color image?
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Frequency and line density
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What happens if you increase the Doppler transmit frequency?
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Increased Doppler frequency shift
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What happens if you increase the Doppler angle?
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Doppler frequency shift decreases
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The velocity estimation would have the greatest error at Doppler angle?
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70 degrees
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Another term for ensemble length or dwell time is
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Packet size
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Which of the following occur to Doppler frequency shift with high velocity in the vessels?
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Increased frequency shift
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The appearance of the spectral window on the spectral waveform display is affected by
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All of above, turbulent flow, Doppler gain, sample volume size
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What must be known to calculate the velocity from the Doppler shift information?
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All of the above, Doppler frequency, angle of incidence, speed of sound in tissues
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Which control would you use to increase the amplification of the color Doppler signal?
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color gain
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Which of the following could result in color Doppler display?
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Any of the above, blood flow, motion from respiration, cardiac motion, transducer motion
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Which control removes low frequency and display a clean zero baseline?
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High pass filter
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Continuous wave (CW) Doppler
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does not alias
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Although the signals from CW Doppler are not as complex, only pulsed Doppler can do
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Depth location
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Which of the following is / are true of pulse Doppler?
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Determines depth by echo arrival time
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CW Doppler does not alias because
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the transducer is continuously sending and receiving with shows the changing flow patterns rather than sampling at interval
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Statement is not true of CW Doppler?
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Aliasing can occur at the very high frequency
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In pulse Doppler, which of the following do not affect the shape and size of the sample volume?
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Spectral scale range (this applies only to the processing of the echo that are received)
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When measuring flow velocity, the pixel color represents
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Movement of both blood and /or tissue
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When comparing CW and pulse wave Doppler which apply?
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CW has a duty cycle of 1.00
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If the returning Echoes have a lower frequency than the transmitted frequency, the reflector is
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Moving away from the transducer
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If the flow is toward a transducer of 2 MHz, the frequencies of the Doppler shift should be _____ 2MHz
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Much less than
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If a 5 MHz transducer display a peak shift of 12 kHz, what shift would the same vessel display with a 2.5 MHz transducer
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6 kHz
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If a Doppler shift of 3 kHz is displayed with an angle of 40 degrees, what will the shift be at 60 degrees?
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Less than
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If the scanner does not have the ability to display the spectral analysis waveform, it will not show
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The distribution of the range of frequencies
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The range gate determines
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The sample volume length along the length of the beam direction
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The frequency of the Doppler samples is determined by the
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The pulse repetition
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Aliasing is more likely at lower Doppler frequency when the sample is
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Farther from the transducer
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Adjustments to overcome aliasing do not include
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Using a higher fundamental frequency
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Range (depth) discrimination is poorest with
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CW Doppler
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If you increase the packet size (ensemble length), the result is
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Better velocity estimation with lower frame rate
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The term variance refers to
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velocity range (laminar flow has less, turbulent flow has more)
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The most accurate measurement of velocity distribution is with
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pulsed Doppler
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The scanning term that display gray scale and a spectral waveform is called
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Duplex scanning
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