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