Unit 2: Doppler
It is critical to identify the doppler angle because of the:
- ability to determine flow direction - ability to assess Doppler measurement accuracy - ability to minimize Doppler error sources - ability to assess likelihood of artifact related issues such as spectral broadening
What are the disadvantages of CW doppler transducers?
- the exact location of the moving RBC's cannot be determined - signals arise from all blood cells in the region of overlap between the transmit and receive beams - collects data from all along the scan line and has no sample gate - lack of TGC
When an angle of ___ degrees or ___ degrees between the direction of motion and the sound beam, the measured velocity is equal to the true velocity because the cosine of these angles is 1.
0, 180
When it comes to the differences between imaging and doppler, doppler occurs at:
0-180 degrees, lower frequencies, pulsed or continues wave
CW doppler transducers have duty factor of ___ or ___.
1, 100%
What are the 3 characteristics that color is based on?
1. hue 2. saturation 3. luminosity
The nyquist limit is ___ of the PRF.
1/2
The first color flow images were produced in ___.
1985
Signal processing signifies that the information is detected at ___ different phases that are ___ degrees apart.
2, 90
Doppler shift range from ___ Hz to ___ kHz.
20, 20
A typical value of doppler frequency is ___ Hz, meaning they are audible.
2000
The color box can be steered in ___ different directions, changing the angle left to right by a maximum of ___ degrees.
3, 25
The human visible dynamic range is less than ___ dB.
36
We should always attempt to use between ___ and ___ degrees for the doppler equation data.
45, 60
We can eliminate aliasing by also using ___ doppler.
CW
For PW, the upper limit of the ___ is determined because we know it takes the pulse a certain amount of time to reach the reflector and return to the t/d.
PRF
___ is the number of times the pulse repeats itself within one second.
PRF
Aliasing occurs when the doppler shift exceeds ___.
PRF/2
What is the equation for resistive index (RI)?
PSV - EDV / PSV
What is the equation for pulsatility index (PI)?
PSV - EDV / average
Aliasing only occurs with ___, not ___.
PW, CW
Doppler shifts are created when sound bounces off of ___.
RBC's
What is the advantage of CW doppler transducer?
able to measure very high velocities
If there is no color invert on, flow toward the t/d is represented by the color ___ the baseline.
above
Directionality is determined by the doppler equation with spectral doppler and a positive shift will be ___ the baseline, while a negative shift is ___ the baseline.
above, below
How do we find the measured velocity?
actual velocity x cosine angle
If the PRF is twice the doppler shift, no ___ will ocur.
aliasing
___ appears when the doppler shift exceeds the nyquist frequency limit.
aliasing
The gray shades of a spectrum are related to the ___ of the reflected signal or the number of ___ ___ causing the reflection.
amplitude, blood cells
New scanners provide a color map of blood flow superimposed onto the ___ ___.
anatomical map
If color is not seen, we can change the ___ and ___ ___ to see if it helps.
angle, wall filter
Color flow only gives an estimate of the ___ or ___ velocity.
average, mean
There is no ___ ___ needed with CW transducer.
backing material
What are the most common clinical doppler devices?
bi-directional
___ is a more sophisticated doppler system which distinguishes between flow towards the t/d and flow away from the t/d by the appearance of positive and negative doppler shifts.
bi-directional
How can we speed up the frame rate when using color doppler?
by adjusting the size of the imaged field in the color mode
How can we correct aliasing?
by increasing our scaes (PRF)
On spectral displays, low frequency shift appear along the baseline and are known as ___.
clutter
Autocorrelation is used with ___ ___ because of the enormous amount of doppler information that requires processing.
color doppler
___ ___ has the worst temporal resolution of all the u/s modalities.
color doppler
___ ___ is a good tool for surveying a large region of the patient, pulsed ultrasound technique.
color flow
___ is a digital computer based-technique used to analyze color flow doppler signals.
color flow
___ ___ is an effective method to detect turbulence, which will show many velocities present from different regions.
color variance
If there is motion toward the transducer (observer), the wavelength will be ___, which will result in a ___ doppler frequency shift.
compressed, positive
The doppler shift depends on the ___ of the angle between the sound beam and the direction of motion.
cosine
___ is a mirror image artifact of the doppler system.
crosstalk
If there was actual flow reversal, the colors would go straight the black baseline from ___ ___ to ___ ___.
dark red, dark blue
If the motion is away form the observer (t/d), the wavelength will be ___, and the change in frequency will be a ___ frequency shift.
decompressed, negative
We the color box is steered, the t/d sensitivity will ___.
decrease
Doppler shift is a low frequency that "rides" on top of the much higher transducer frequency and is usually extracted by the ___.
demodulation
___ occurs when the reflected signals from the stationary structures are subtracted from the combined signal, leveling the frequency shifted information.
demodulation
The colors on the color bar determine the ___ and the ___ ___.
direction, mean speed
Doppler shift is ___ proportional to the t/d frequency.
directly
Doppler shift is ___ related to velocity and t/d frequency.
directly
Why do we want to see all of the components of the frequency with FFT?
distinguishes laminar flow from turbulent flow
Aliasing occurs when it is not possible to increase the ___ ___ anymore.
doppler scales
The change in frequency of a sound wave is known as the:
doppler shift or doppler frequency
___ ___ is a technique that utilizes the fact that the frequency of sound changes when it is reflected from a moving surface.
doppler ultrasound
___ ___ is a machine that can perform both imaging and doppler.
duplex imaging
What is the doppler shift equation?
fD= 2fov cos/c
True or false: we can use color to find true velocity.
false
A ___ ___ ___ is a digital technique that is use to process both pulsed and continuous wave doppler.
fast fourier transform
Autocorrelation is slightly less accurate, but is substantially ___ than FFT.
faster
The greater the velocity, the greater the ___ ___.
frequency shift
The doppler equation is a mathematical relationship between the ___ ___ and the ___ of RBC's that produce it.
frequency shift, velocity
Increasing the ___ can cause the color noise floor to become visible as color speckle within the image.
gain
___ occurs with color displays right outside of the packet.
ghosting
What is a problem with gray scale imaging that conflicts with doppler?
gray scale imaging requires the optimal angle between the sound beam and reflectors to be 90 degrees, which means no doppler shift could be measured
With PW doppler, aliasing occurs at very ___ velocities in one direction that incorrectly displayed as going in the opposite direction.
high
When aliasing occurs, the audible doppler signal exhibits a noticeable loss of ___ frequencies as the frequency exceeds the maximum. It also sounds as though ___ ___ occurs.
high, flow reversal
If the sample volume is shallow, PRF is ___, so the nyquist limit is ___.
high, increased
For superficial vessels, we use ___ frequency. For deep vessels, we use a ___ frequency.
high, low
___ frequency t/ds alias more than ___ frequency t/ds.
high, low
___ frequency t/ds have more of a shift than ___ frequency.
high, low
Blood cells moving toward the t/d will cause a ___ shift, meaning the reflected frequency is higher than the transmitted frequency.
higher
According to the doppler effect, if the source is moving towards the t/d, the frequency will be ___ and the wavelength will be ___. This indicates a ___ frequency shift or change.
higher, shorter positive
On a spectral display, the time is the ___ axis and the frequency shift is the ___ axis.
horizontal, vertical
The pulse-echo scanner and the doppler instrument compliment each other, one gives ___ ___ and the other provides information about ___ ___.
imaging detail, flow patterns
What are the disadvantages of PW doppler?
inability to correctly measure high velocities
How should we set the color gain?
increase the gain until noise speckle appears and then decrease the color gain until the color speckle
As the wall filter is ___, the doppler signals from the baseline is lost.
increased
What are the advantages of power doppler?
increased sensitivity, and gives improved edge definition around plaque, etc
When the color box is steered, the angle ___ and maintaining the ___ must be compromised.
insonation, sensitivity
When identifying the doppler angle, we must identify whether it is an ___ angle or an ___ angle.
insonification, insonation
What are the advantages of FFT?
it is exceedingly accurate and it displays all individual velocity components that make up the complex reflected signal
With ___ flow, most blood cells within the sample volume travel at similar velocities.
laminar
We cannot usually visualize the difference of steering the color box with ___ vessels. However it becomes a problem when looking at ___ vessels.
large, smaller
Colors on the ___ side of color map indicate laminar flow, and colors on the ___ side indicate turbulent flow.
left, right
A wall filter control is a control of CW that eliminates ___ frequency signals.
low
The wall filter removes ___ frequency doppler signals from the display.
low
If the sample volume is deep, PRF is ___, so the nyquist limit is ___.
low, low
Pulsed doppler transducers have a ___ Q, ___ sensitivity, and ___ bandwidth.
low, lower, wide
When trying to detect low velocity flow with color, you must make certain to ___ the color scale.
lower
According to the Doppler effect, if the source is moving away from the t/d, the frequency will be ___ and the wavelength will be ___. This indicates a ___ frequency shift or change.
lower, longer negative
___ is the brightness of a color.
luminosity
The color bar relates the ___ ___ ___ detected with color.
mean frequency shift
The pulse packet correlates the data from each scanned line to yield an estimated ___ ___.
mean velocity
What are the advantages of a large number pulses in a pulse packet?
more accurate velocity measurement and an increased sensitivity to low flow
What are the disadvantages of a large number of pulses in a pulse packet?
more time needed to acquire data, reduced frame rate, and decreased temporal resolution
PWD using a small sample gate in the center of a vessel will produce a ___ band doppler frequency signal.
narrow
CW transducers have an undampened signal, ___ bandwidth, ___ Q, and ___ sensitivity.
narrow, high, high
Color doppler has a pulse with a ___ frequency bandwith, with is an advantage.
narrower
Do we have to make adjustments or calculations to determine the doppler frequency?
no
Does power doppler suffer from aliasing?
no
Will variations in red blood cell concentration affect the ability to perform a doppler exam?
no
When flow is not detected, it could be from:
no flow, an angle at or close to 90 degrees, or the low frequency shifts were rejected by the wall filters
What are two other names for a uni-directional doppler system?
non-coherent, non-directional
When it comes to the differences between imaging and doppler, imaging occurs at:
normal incidence, higher frequencies, pulsed wave
The ___ ___ ___ is the highest doppler frequency or velocity that can be measured without the appearance of aliasing.
nyquist frequency limit
Aliasing occurs when the doppler frequency exceeds the ___ ___.
nyquist limit
We should always be aware of whether the ___ is on or off so flow direction can be determined.
off
For PW doppler, ___ crystal is necessary.
one
The largest amplitude signals received can be ___ ___ ___ times larger than the smallest signals.
one hundred million
The most accurate doppler measurement is obtained when red blood cells are traveling in a direction ___ to the ultrasound beam.
parallel
Color does not provide ___ ___ or ___ ___ and is subject to aliasing.
peak velocities, spectral broadening
Processing of the signal is performed with ___ ___ or ___ ___.
phase quadrature, quadrature detection
___ doppler provides better definition of the boundaries of the blood flow than ___ doppler.
power, color
Color flow uses a longer ___ ___ than what it used in B-mode imaging.
pulse duration
When using color doppler, the single line that pulses are transmitted along is repeated to create a color or ___ ___.
pulse packet
Multiple pulse echo sequences are required in color flow imaging and are called ___ ___.
pulse packets
What are the advantages of PW doppler?
pulsed doppler enables the precise selection of the depth and angle of the sample volume to be placed on the exact location you want to measure
What separates the signal into its forward and reverse components so that flow directionality is known and shown graphically?
quadrate detection
What are some ways to avoid aliasing?
raise the nyquist limit, reduce the doppler shift, locate another scanning window in which the incident angle is closer to 90 degrees, and by using a low frequency t/d
When signals arise form all blood cells in the region of overlap between the transmit and receive beams, it is called ___ ___.
range ambiguity
What are the pulsed doppler controls?
range gate position, gate or sample volume size, and flow angle cursor
Before each pulse is launched in aliasing, the machine waits for the preceding one so that ___ ___ can be acquired.
range resolution
___ scattering occurs when the diameter of the reflector is small relative to the wavelength of the interrogating wave.
rayleigh
What are the three primary color hues?
red, blue, and yellow
How do we find the doppler shift (Hz)?
reflected frequency - transmitted frequency
Autocorrelation estimates the ___ ___.
reflector velocities
For color flow, the more pulses in a packet, the better the estimates of the ___ ___. However, we will have slower image ___ ___ and poor ___ resolution.
reflector velocities, frame rates, temporal
The shift of frequency is actually the result of changes which occur to the wavelength of sound because of the ___ ___.
relative motion
The Doppler effect describes an apparent shift of any interrogating wave cause by ___ ___ between the ___ and the ___.
relative motion, observer, target
PW doppler has range ___.
resolution
During laminar flow, the velocities are nearly the ___ for each pulse and the variance is ___.
same, small
___ is amount of white in color that creates the shades of colors.
saturation
The color is usually located at the ___ of the image.
side
Doppler has an increased output because of the beam dwelling along a ___ acoustic line, instead of like b-mode, sweeping a region.
single
What does the baseline shift do?
slides the baseline down so that the entire scale is devoted to one direction
According to the wall filter theory, the reflectors that cause the clutter signals are moving ___ compared to most blood flow.
slowly
The doppler effect describes the change in observed frequency due to the relative motion between the ___ and the ___.
source, observer
With turbulence, blood flow is chaotic and will cause the spectral window to be filled with turbulent flow, which is known as ___ ___.
spectral broadening
The region between the baseline and the spectrum called the ___ ___, is clear.
spectral window
Doppler ultrasound determines the ___ and ___ of blood as it courses through the cardiovascular system.
speed, direction
What does bi-direcitonal audio require?
stereo headphones, speakers, or a display that can represent flow towards the transducer above the baseline and flow away from the transducer below the baseline
What does the black represent on the color bar?
the baseline and where the wall filtering occurs
What does the 2 represent in the doppler equation?
the fact that there is double doppler shift when a sound beam strikes a blood cell. The first shift occurs when the sound wave strikes the cell, the second shift is a result of the moving blood cell re-radiating the wave back to the transducer
What happens if we do not lower the color scale when detecting signals?
the integrated wall filters will be too high and will eliminate the very signals we are trying to detect
The returning signal from doppler shift detection is a combination of back scattered data from ___ and from frequency shifted data from ___ ___.
tissue, moving targets
What are the disadvantages of power doppler?
to improve sensitivty, a high degree of frame averaging is used, which means that the operator has to keep the t/d very still to obtain a good image,
When aliasing occurs, flow towards the t/d will extend to the ___ of the spectrum and then continue on the ___ of the spectrum.
top, bottom
With color, it wraps from the color at the ___ of the color bar to the color which appears at the ___ of the color bar.
top, bottom
The Doppler effect is the difference between the ___ ___ and the ___ ___ from a moving structure.
transmitted frequency, frequency reflected
True or false: According to the Doppler effect, if both objects are stationary, the same frequency will be observed.
true
True or false: color flow does not give full spectral information.
true
True or false: dedicated CW sound cannot be used for imaging, only pulsed sound can create images.
true
True or false: the mean velocity can also be obtained from the spectrum.
true
True or false: uni-directional means we cannot distinguish whether blood is flowing towards or away from t/d.
true
If the PRF is less than ___ the frequency of the maximum doppler signal frequency, aliasing occurs.
twice
Continuous wave doppler system requires ___ crystals.
two
We must work to make the PRF great enough to sample the doppler signal at least ___ times for each cycle of the doppler signal.
two
___ is a basic doppler system that simply measures the presence of moving blood cells by the appearance of a doppler shift.
uni-directional
Crosstalk will provide an identical analysis on both sides of the baseline. The flow will be ___ but appears to be ___.
unidirectional, bi-directional
The ___ ___ distinguished laminar from turbulent.
variance mode
A frequency shift is always related to ___.
velocity
With doppler, we are only interested in the ___ of the moving structures.
velocity
If we want to eliminate aliasing, we need to adjust the ___ ___ on the display.
velocity scale
With spectral doppler, we have separate controls for ___ ___ and ___ ___.
velocity scales, wall filtering
The technique for filtering out clutter signals is called ___ ___.
wall filtering
