Physics Doppler Effect

what is the cosine of 180

-1

the functions of a doppler detector include

-amplification -phase quadrature detection -doppler shift detection -sign determination

stenosis effects what in the spectral analysis?

-peak systolic flow speed -end diastolic flow speed -spectral broadening

as a stenosis progresses, what increases?

-systolic doppler shift -diastolic doppler shift -spectral broadening

What is the cosine of 60?

.5

at what angles between the sound beam and the direction of motion will the doppler shift be the highest?

0 or 180

b-mode imaging requires at least ____ pulse

1

the cosine of 0 is

1

What are the two terms used to describe PW's ability to select the exact location where velocities are measured?

1) range resolution 2) range specificity

What 5 pieces of information does Autocorrelation contain?

1. Doppler Shift 2. Mean 3. Sign 4. Variance 5. Power

What are five techniques that can be used to avoid aliasing artifact?

1. adjust the scale to its maximum 2. select a new ultrasonic view with a shallower sample volume 3. select a lower frequency transducer 4. use baseline shift 5. use continuous wave doppler

The functions of a doppler detector include what 4 things?

1. amplification 2. phase quadrature detection 3. doppler shift detection 4. sign determination

What are the 4 forms of doppler presentation?

1. audible 2. color doppler 3. spectral doppler 4. strip-chart recording

the doppler sample volume is determined by what three things?

1. beam width 2. gate length 3. emitted pulse length

3 factors that create more aliasing

1. faster blood velocity 2. higher frequency transducer 3. deep gate (low PRF)

Lack of color in a vessel containing blood flow may be attributable to what 3 things?

1. low color gain 2. a high wall filter setting 3. a low priority setting

Compared with doppler-shift imaging, doppler-power imaging is what 4 things?

1. more sensitive 2. angle independent 3. aliasing independent 4. speed independent

flow information provides what 4 things?

1. presence of flow 2. direction of flow 3. speed of flow 4. character of flow

What are two ways to avoid aliasing?

1. raise the Nyquist limit 2. lower baseline

3 factors that create less aliasing

1. slower blood velocity 2. lower frequency transducer 3. shallow gate (high PRF)

the amount of increase or decrease in doppler frequency depends on what 3 things?

1. speed 2. angle 3. frequency of the wave emitted

Autocorrelation produces what 2 things?

1. the mean value of the Doppler shift 2. variance

What are the two things that a good doppler angle is critical for?

1. to determine flow direction 2. to accurately determine speed

dedicated continuous wave transducers do not use backing material, which results in the following 4 things:

1. undampened transmitted signal 2. narrow bandwidth 3. high quality factor 4. higher sensitivity

In a single frame, color can change in a vessel because of what 4 things?

1. vessel curvature 2. sector format 3. helical flow 4. diastolic flow reversal

In practice, approximately _____ pulses are required to obtain one line of color info

10

What is the average ensemble length?

10-20

how many crystals are present in CW doppler?

2

If angle correction is set at zero degrees but should be 60 degrees, the display indicates a flow speed of 100 cm/s. The correct flow speed is

200 cm/s

What is the minimum ensemble length?

3

How many frames per second are produced by a color Doppler instrument?

40 or less

doppler instruments have pulse lengths of how many cycles?

5-30

If a 5-kHz Doppler shift corresponds to 100 cm/s, then a 2.5 kHz shift corresponds to _____ cm/s

50

If angle correction is set at 60 degrees but should be zero degrees, the display indicates a flow speed of 100 cm/s. The correct flow speed is.

50 cm/s

Frame Rate in Color

77,000/depth x LPF ensemble length

Grayscale imaging is best performed at what angle?

90 degrees

what is the duty factor in PW doppler?

<1%

Color Doppler instruments use an _______ technique to yield Doppler info in real time

Autocorrelation

What is the typical range of Doppler shift found in diagnostic imaging examinations?

Between 20 Hz and 20 kHz (in the audible range)

A region of bright color on a doppler shift display always indicates the highest flow speeds. True or false.

False

Angle is not important in transverse color Doppler views through vessels. True or False.

False

doppler ultrasound provides information about flow conditions only at the site of measurement. True or False.

False

Higher flow speed always produces a higher doppler shift on a spectral display. True or False.

False (remember the doppler angle)

How is "doppler shift" represented in equations?

Fd

What is the doppler equation?

Fd = 2x Fo x v x cosθ /c

Color Doppler instruments present two-dimensional, color-coded images representing ___________ that are superimposed on gray-scale images representing __________

Flow or motion, anatomy

How is the operating frequency represented in equations?

Fo

What is presented in real time on a color Doppler display

Gray-scale anatomy and flow direction

What is the unit of doppler shifts?

Hz

The larger the Doppler angle the [lesser, more] the Doppler shift

Lesser

The very top of a doppler display is called the

Nyquist limit

What is the Nyquist Limit (formula)

PRF(Hz)/2

What type of Doppler is not angle dependent?

Power Doppler

what formula is used to yield effective sample volume length?

SPL/2

formula to determine velocity

V = Fd x C/ 2 x Fo x cos(theta)

When is the blood cell velocity 100% accurate?

When blood cells are moving parallel to the sound beam

What is the doppler effect?

a change in frequency caused by the motion of a sound source

an earlier gate time means _____ sample volume depth

a shallower

What is the primary advantage of PW doppler?

ability to select the exact location where velocities are measured

What is the advantage of CW doppler?

able to display high velocities without aliasing

What is the biggest disadvantage of PW doppler over CW?

aliasing

the part of a doppler spectrum that wraps around and appears at the bottom of the screen is called

aliasing

Which is typically higher, arterial or venous velocities?

arterial

The _____ technique is commonly used to detect echo Doppler shifts in color Doppler instruments?

autocorrelation

power doppler uses _____ to detect the strength of the doppler shift

autocorrelation

the width of the sample volume is equal to the

beam width

Why is the measured velocity zero when the direction of flow is perpendicular to the sound beam?

because the cosine of 90 is zero

If an instrument distinguishes between positive and negative doppler shifts, it is called

bidirectional

Color map baselines are always represented by what color?

black

the doppler shift is proportional to the

blood flow

doppler signal power is proportional to

cell concentration

Can you control PRF in B-mode or Color?

color

Ensemble length AKA

color packet

for blood flowing in a vessel with a plug flow profile, the doppler shift is ____ across the vessel

constant

when incident sound direction and reflector motion are not parallel, calculation of the reflected frequency involves the ______ of the angle between these directions

cosine

With constant flow speed and source frequency an increase in doppler angle creates a _____ in doppler shift

decrease

If cosine is increased velocity is

decreased

If doppler angle is doubled, the doppler shift is

decreased

Increasing the ensemble length _____ the frame rate

decreases

as the angle indicator increases, the cosine

decreases

the process of extracting the low Doppler frequency from the transducer's carrier frequency is called

demodulation

range gating enables what two things?

depth selectivity and a small doppler sample volume

echo voltages from the transducer are processed in the

detector

What does zero crossing do?

detects motion above or below the baseline

The measurement of the doppler frequency depends on the relationship between what two things?

direction of blood flow and the direction in which the sound wave propagates

how is speed reported?

distance over time

to proceed from a measurement of doppler shift frequency to a calculation of flow speed, what must be known or assumed?

doppler angle

What do you call the many different doppler shifts received from the vessel by the system?

doppler frequency spectrum

the y-axis of a doppler spectrum represents

doppler shift or velocity

How do you acquire flow information?

doppler ultrasound

the ______ effect is used to detect and measure ______ in vessels

doppler, flow

If a transducer's frequency is doubled the measured doppler shift will

double

simultaneous anatomic imaging and doppler is called

duplex imaging

What is increased if doppler angle is increased?

effect of angle error

Doppler shift displays are not dependent on Doppler angle. True or False?

false

If a color Doppler instrument shows two colors in the same vessel, it always means flow is occurring in opposite directions in the vessel. True or false?

false

True or False. Shallower sample volumes result in more aliasing

false

the [slower, faster] the velocity, the greater the doppler shift

faster

Doppler shift is directly related to the ______ of the transmitted sound

frequency

motion of an echo-generating structure causes an echo to have a different _____ from that of the emitted pulse

frequency

The doppler effect is presented as a ______ when the source and the receiver are ________

frequency shift, in motion relative to each other

the faster the velocity the [lesser, greater] the doppler shift

greater

doppler measurements are not reliably achieved at doppler angles

greater than 60 degrees

When the measured velocity is at 60 degrees it is what percent of the actual velocity?

half

Doubling the width of a color window produces a ______ frame rate

halved

If the cosine (theta) is reduced by half the doppler shift will be

halved

When the velocity is halved the doppler shift is

halved

flow reversal in diastole indicates

high distal resistance

When the sample volume is shallow, the PRF is [low, high] and the Nyquist limit is [low, high]

high, high

In a positive doppler shift the received frequency is [lower, higher] than the transmitted frequency

higher

what is slowed to allow for the acquisition of doppler information between frames?

imaging frame rates

A shorter gate length does what in a spectral display?

improves the quality

Increasing ensemble length _____ color sensitivity and accuracy and _____ frame rate

improves, decreases

With constant flow speed and source frequency a decrease in doppler angle creates a ______ in doppler shift

increase

decreased distal resistance normally causes end diastolic flow to

increase

if doppler angle is increased then velocity is

increased

doppler angle and cosine have a(n) _______ relationship

inverse

What is the doppler equation for?

it is used to quantify the doppler effect

What type of situation does the lack of TGC's create in CW ultrasound?

it may falsely appear that deeper vessels have less flow

What is another disadvantage of CW ultrasound besides range ambiguity?

lack of TGCs

the doppler sample volume in CW is [small, large]

large

When an angle exists between the direction of flow and the sound beam, the measured velocity is [less, more] than the true velocity

less

color doppler frame rates are ____ gray-scale rates

less than

Aliasing occurs when the doppler sampling rate is too ______ in comparison to the measured blood velocities

low

When the sample volume is deep, the PRF is [low, high], and the Nyquist limit is [low, high]

low, low

Pulsed wave doppler has ______ quality factor, _____ sensitivity, and _____ bandwidth pulses

low, low, wide

In a negative doppler shift the received frequency is [lower, higher] than the transmitted frequency

lower

speed is purely a

magnitude

velocity is defined by a

magnitude and a direction

Color doppler measures ____ velocity while spectral doppler measures ______ velocity

mean, peak

higher frequency transducers create [less, more] aliasing

more

what is required for doppler effect?

motion

When blood cells move away from the transducer, the Doppler shift is [negative, positive]

negative

Disadvantages of Power Doppler

no flow direction info no speed info no flow characteristics info

What is the disadvantage of CW doppler?

no imaging

what is the main disadvantage of selecting a new ultrasonic view with a shallower sample volume to reduce aliasing?

none

Advantages of Power doppler

not dependent on doppler shift formula no aliasing no angle dependence more sensitive to slow flow and small vessels

What is the job of the two crystals in a CW transducer?

one continuously sends, the other continuously receives

doppler shifts are typically ________ of the operating frequency

one thousandth

in CW, doppler shifts are determined by mixing the returning voltages with the CW voltage from the

oscillator

The cosine gives the component of the flow velocity vector that is _______ to the sound beam

parallel

What is the commonly used signal processing technique for bi-directional doppler?

phase quadrature, or quadrature detection

When blood cells move toward the transducer, the Doppler shift is [negative, positive]

positive

Doppler-power imaging indicates (with color) the ____ of flow

presence

Doppler-shift imaging indicates (with color) the _(4)__ of flow

presence, direction, speed, character

spectral analysis does what with doppler shift frequencies?

presents them in frequency order

What is the Pulsed Wave operating frequency equation?

propagation speed / 2 x crystal thickness

color doppler has high ______ resolution

range

What do you call the overlap between the transmit and receive beams in CW ultrasound?

range ambiguity

through _______, pulsed wave doppler has the ability to select information from a particular depth along the beam

range gating

the doppler shift is the difference between _____ and _____ frequencies

received, emitted

what are the reflectors in human circulation?

red blood cells

what is the main disadvantage of adjusting the scale to a maximum to avoid aliasing?

reduces sensitivity to low velocities

what does the wall filter do?

rejects frequencies below an adjustable value

range gate aka

sample volume

What do you call a marker that shows where doppler information is being obtained from?

sample volume/gate

longer gate lengths are used when

searching for a desired vessel and flow location

most importantly, continuous wave transducers have increased

sensitivity

the spectral display is a presentation of doppler _____ versus ______

spectra, time

shorter gate lengths are used for

spectral analysis and evaluation

In continuous wave, doppler shifts are commonly sent through a _______ to a _______

spectrum analyzer to a spectral display

power doppler uses autocorrelation process to detect the _____ of doppler shift instead of the _______ that color doppler uses

strength, mean value

Is the system able to more accurately measure velocities in deep or superficial structures?

superficial

The frequency at which aliasing occurs is called

the Nyquist Limit

What can be thought of like a speed limit?

the Nyquist limit

The sampling rate of pulsed doppler is the same as

the PRF

What is the doppler angle defined as?

the angle between the sound beam direction and the direction of flow

what is the doppler effect?

the change in frequency/wavelength of a sound that results from motion

What determines the strength of power doppler?

the concentration of moving reflectors producing Doppler shift

What is the unit of power doppler?

the concentration of reflectors

The percentage of the true velocity that is measured depends on

the cosine of the angle between the sound beam and the direction of motion

How do you determine the doppler shift?

the difference between the received frequency and transmitted frequency

Steering the color window to the right or left changes what two things?

the doppler angle and the doppler shift

what determines the frequency in a CW transducer?

the drive voltage frequency

Modern ultrasound systems actually measure what in hertz between the received and transmitted sound waves?

the frequency difference

What is Fast Fourier Transform?

the mathematical technique the instrument uses to derive the doppler spectrum

What is ensemble length?

the number of pulses used for each scan line

In CW, the sample volume is where?

the overlapping region of the transmitting and receiving beams

Which portion of the motion contributes to the doppler effect?

the portion that is parallel to the sound beam

What is doppler shift?

the quantitative measurement of doppler effect

Where does auto-correlation occur?

the signal processor

what removes clutter?

the wall filter

Why is there a "2" in the doppler equation?

there are actually two doppler shifts

how are frequency shift and doppler shift related?

they are the same thing

what determines the frequency in a pulsed wave transducer?

thickness of crystal

If all the cells in a vessel were moving at the same constant speed, the spectral trace would be a

thin horizontal

color doppler requires at least _____ pulses

three

The x-axis of a doppler spectrum represents

time

True or False. The higher the emitted frequency, the more likely a pulsed wave signal is to alias

true

True or false. Only pulsed wave doppler exams have a sample volume.

true

measured velocity =

true velocity x cos(θ)

What type of flow is synonymous with spectral broadening?

turbulent flow

common causes of spectral broadening

turbulent or disturbed flow over gain sample volume too wide incorrect placement of sample volume

Steering the color window to the right or left produces a _____ frame rate?

unchanged

doppler shift is directly related to the _____ of the blood cells

velocity

What two major things is doppler shift directly related to?

velocity and transducer frequency

Doppler frequencies indicate _____ , not _______

velocity, not speed

Spectral broadening is a ______ of the spectral trace

vertical thickening

What control can be used to help with clutter?

wall filter

Name two things that will reduce the frame rate of a color Doppler image.

wider color window or increased ensemble length

if there is no doppler effect can there still be sound?

yes