The Doppler effect occurs
all echoes from moving sources
Doppler effect depends on
the closing velocity between transducer and tissue, carrier frequency & u/s propagation velocity..
The shape of the sample volume in PW Doppler has a large effect on the content of the Doppler signal
True..
To measure flow velocity with color flow imaging
color a sample volume is placed in the faster streamline and set at angle correction parallel to vessel wall
To form the color flow image, the system samples down each Doppler image scan line for
the average Doppler shift frequency
Separating moving soft tissue from moving blood in a color flow image tests for
The relationship between amplitudes and frequencies of the Doppler signals
The smallest vessels that appear in a color flow image are about 1 mm. diameter. The smaller vessels are absent because
small vessels do not reflect as well as larger vessels do
Detecting color flow depends on
changes in echo signal phase (phase indicates direction for color assignment)
Power Doppler imaging is a good choice for
showing blood perfusion through the tissue
Power Doppler is limited because
It does Not show direction of flow
Turbulence in color flow vascular imaging appears as
A mottled pattern of colors or
mottled pattern of red and blue with changing saturations
What is the maximum velocity limit for a 3 MHz continuous wave Doppler image at 4 cm deep
CW has no maximum limit
Alasing occurs when the frequency shift exceeds
1/2 the PRF
When imaging the portal vein in the liver and no color is detected in the vein, what can you do to improve the sensitivity to flow?
Decrease PRF (decrease PRF for slow flow)
The packet size (or ensemble length) in color Doppler refers to the number of
pulses per scan line
If the Doppler angle of incidence is underestimated, what error will result?
Velocity estimate will be Inaccurate
The processing technique for determining direction in CW Doppler is
Fast Fourier Transform...
What method is used to steer the color box?
electronic time delays
If the frequency of the returning echo is higher than the fundamental transmited frequency, which will occur?
positive shift with red color
The Doppler spectral display shows
relative signal power at each frequency in the Doppler signal
If you increase the wall fiter during Doppler sampling it will:
reduce display of low-frequency shifts
What technique is used to perform the spectral analysis?
Fast Fourier Transform, technique
If you increase the transmit frequency of the color Doppler, what will happen?
improved sensitivity to slow flow
If you lower the color threshold, what will occur?
increased color fill within the vessel
The Doppler frequency shift is defined as
the difference between transmitted and received frequencies
From the Doppler equation, which would NOT be true?
increasing Doppler frequency will incase frequency shift
What does brightness of the Z axis on the Doppler spectrum refer to?
Amplitude
The Nyquist limit refers to
Sampling frequency required for Doppler samples without Aliasing
What can you adjust to improve the frame rate?
(Decrease size of color box & Decrease scan line density)
What adjustments can you make to decrease aliasing?
increase PRF
With the following scan parameters, what is the frequency at which aliasing will occur? 5 MHz fundamental frequency, 3 kHz PRF, 4 cm depth, 1.5 mm sample volume width.
3 kHz (Nyquist limit is PRF)
The faster technique used to obtain the MEAN Doppler frequency in color flow is
Autocorrelation
Color flow imaging in the vascular system usually uses
a linear sequenced (switched) array transducer
If you see spectral broadening in the spectral analysis display, it usually means
turbulent flow
Which of the following refer to the number of pulses used to measure the velocity along one scan line?
packet size & ensemble length
Which analysis method would show turbulence with color Doppler?
variance mode color display
Which term refers to the axial length of the sample volume
color gate
Spectral analysis is used for
Showing the distribution and magnitude of frequency shifts in the Doppler signal
What adjustments can you make to eliminate color flash artifact?
increase wall filter
Which of the following is NOT true for turbulent flow?
causes increase in pressure downstream
Which conditions are most likely produce turbulence?
5 mm diameter with 300 cm/sec velocity (Reynolds number = average speed x diameter x density)
Which of the following are true regarding color Doppler images?
Doppler color image is superimposed over the B mode image
Which of the following will decrease frame rate?
increasing line density
When using Duplex scanning, how many pulses per san line are usually used to create the gray scale image?
1-2
If you increase the packet size, what will result?
decreased frame rate
Which control on the control panel adjusts Doppler PRF?
Spectral velocity scale
When you increase the Doppler frequency, what occurs?
Increased Doppler frequency shift
What should you adjust to improve color Doppler sensitivity to flow?
lower wall filter setting
If you lower the PRF, which of the follow occur?
Nyquist limit is decreased
What part of the Doppler spectrum in color-encoded with color Doppler
the frequency shift
What color would represent flow at 90 degrees to the sound beam?
black
What color is usually represented as moving toward the transducer?
red
Why does the frame rate decrease when adding color to the gray scale image?
more pulses are required for each scan line
Which control determines the gray-scale brightness at which color willdisplay instead of gray-scale?
priority
With reference to the Doppler equation, the frequency shift will increase by increasing the ________
Transmit frequency
What affects the spatial resolution of the color image?
frequency and line density
What happens if you increase the Doppler transmit frequency?
increased Doppler frequency shift
What happens if you increase the Doppler angle?
Doppler frequency shift decreases
The velocity estimation would have the greatest error at which Doppler angle?
70 degrees
Another term for ensemble length or dwell time is:
packet size
Which of the following occur to Doppler frequency shift with high velocities in the vessels?
increased frequency shift
appearance of the spectral window on the Spectral waveform display is affected by
(Turbulent flow, Doppler gain, Sample volume size)
ALL OF THE ABOVE
What must be known to calculate the velocity from the Doppler shift information?
(Doppler frequency, Angle of incidence, speed of sound in tissue)
All of the above
Which control would y you use to increase the amplification of the color Doppler signal?
color gain
Which of the following could result in color Doppler display?
(Blood flow, Motion from respiration, Cardiac motion, transducer motion)
Any of the above
Which control removes low frequencies and displays a clean zero baseline?
high pass filter
Continuous wave (CW) Doppler
does not alias
Although the signals from CW Doppler are not as complex only pulsed doppler can do
depth location
Which of the following is true about pulsed Doppler?
determines depth by echo arrival time
CW Doppler does not alias because
the transducer is continuously sending and receiving which shows the changing flow patterns rather than sampling at intervals
Which statement is NOT true of CW Doppler?
aliasing can occur at the very high frequencies always
In pulsed Doppler, which of the following do not affect the shape and size of the sample volume?
spectral scale range
When measuring flow velocity, the pixel color represents
movement of both blood and/or tissue
When comparing CW and pulsed wave Doppler, which apply?
CW has a duty cycle of 1.00
If the returning echoes have a lower frequency than the transmitted frequency, the refector is
moving away from the transducer
It the fow is toward a transducer of 2 MHz, the frequencies of the Doppler shift should be ____________ 2 MHz
much less than
Ifa 5 MHz transducer displays a peak shit of 12 kHz, what shift would the same vessel display with a 2.5 MHz transducer?
6 kHz
If a Doppler shift of 3 kHz is displayed with an angle of 40 degrees, what will the shift be at 60 degrees
less than
H the scanner does not have the ability to display the Spectral analysis waveform, it will not show
the distribution of the range of frequencies
The range gate determines
volume the sample volume length along the length of the beam direction
The frequency of the Doppler samples is determined by the
The pulse repetition
Aliasing is more likely at lower Doppler frequencies when the sample is
farther from the transducer
Adjustments to overcome aliasing do NOT include
using a higher fundamental frequency
Range (depth) discrimination is poorest with
CW Doppler
If you increase the packet size (ensemble length), the results is
better velocity estimates with lower frame rate
The term variance refers to
velocity range
The most accurate measurement of velocity distribution is with
Pulsed Doppler
The scanning term that displays gray scale and a spectral waveform is called
Duplex scanning