Doppler Presentation

•Doppler Principles•Doppler Principles•Color Principles

Color/DopplerColor/DopplerColor/DopplerColor/Doppler

Doppler PrinciplesDoppler PrinciplesColor Principles

The Doppler ConceptThe Doppler ConceptThe Doppler ConceptThe Doppler Concept

Moving objects and stationary objectssound differently to the observer...

To the observer,the engine soundappears to fall pitch


Moving objects and stationary objectssound differently to the observer...

To the observer, the engine sound appears to rise in pitch

While this plane on theground appears to havea constant pitch

An AnalogyAn AnalogyAn AnalogyAn Analogy

You can think of it as a moving object that either

compresses or stretches the sound wave , thus changing

its frequency.


You can think of it as a moving object that either

compresses or stretches the sound wave , thus changing

Ultrasounde

Doppler EffectIn ultrasound Imaging, echoes received from most ti ssues will be at the same frequency as the transmitted beam. However, if echo es received are from tissues or blood cells that are moving, the transmi tted and received frequencies

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tissues or blood cells that are moving, the transmi tted and received frequencies will not be the same. This “shifted” frequency can be used to determine the relative velocity and the direction of this moving tissues. This effect is known as the Doppler Principle . Essentially, the greater the frequency shift, the higher the ve locity of the moving object. Additionally, mo vement toward the transducer results in a higher received frequency, and movemen t away in a lower received frequency.


In ultrasound Imaging, echoes received from most ti ssues will be at the same frequency as the transmitted beam. However, if echo es received are from tissues or blood cells that are moving, the transmi tted and received frequencies tissues or blood cells that are moving, the transmi tted and received frequencies

frequency can be used to determine the relative velocity and the direction of this moving tissues. This effect is known as

. Essentially, the greater the frequency shift, the higher the ve locity of the moving object. Additionally, mo vement toward the transducer results in a higher received frequency, and movemen t away in a lower received

UltrasoundeDoppler Effect

TXM

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RCV

If the reflector is moving toward the transmitter, the received frequency will be higher than the transmitfrequency.


TXM

RCV

If the reflector is moving toward the transmitter, the received frequency

If the reflector is traveling awayfrom the transmitter, the received frequency will be lower than thetransmit frequency.

Doppler ConceptDoppler ConceptDoppler ConceptDoppler Concept

When sound strikes a blood cell,the echo bounces back at thesame frequency

And when the blood cell is movingtowards the sound source,the reflectedecho will be at a higher frequency

•You can think of it as the movement of the blood stretching or compressing the sound wave, thuschanging the frequency.

•Doppler instruments measure this change in frequency in order to determine velocity.


But when the blood cell is moving awayfrom sound source,the reflected echo will be at a lower frequency.

reflected

You can think of it as the movement of the blood stretching or compressing the sound wave, thuschanging the frequency.

Doppler instruments measure this change in frequency in order to determine velocity.

Ultrasounde

Spectral Doppler

Spectral Doppler, of high value in ultrasound diagn osis, can be used for

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Spectral Doppler, of high value in ultrasound diagn osis, can be used for evaluation of blood flow, includes two kinds:

- Pulse Doppler (PW)

- Continuous Wave Doppler


Spectral Doppler, of high value in ultrasound diagn osis, can be used for Spectral Doppler, of high value in ultrasound diagn osis, can be used for evaluation of blood flow, includes two kinds:

(PW)

Continuous Wave Doppler (CW).

Pulse Doppler

In Pulse Doppler, the transducer emits few

cycles of pulses at a time into the human body.Echoes reflected from moving structureincluding blood cells, experience a Doppler shift in frequency.Using the Doppler equation, the echo Using the Doppler equation, the echo information obtained within the ‘SampleVolume’ is analyzed for shifted frequency Content and displayed as a graphic waveformwhich gives information about blood flow velocityat a particular point in vessel. .


the transducer emits few

cycles of pulses at a time into the human body. Pulse DopplerPulse Doppler

Single Transducer

is analyzed for shifted frequency Content and displayed as a graphic waveformwhich gives information about blood flow velocity

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θθθθRange Gate

A Doppler ProcessorA Doppler ProcessorA Doppler ProcessorA Doppler Processor

• The Doppler processor puts a dot on the “spectrum” based on the velocity of a moving object.object.


Doppler ProcessorDoppler ProcessorDoppler ProcessorDoppler Processor

• When there are objects moving at different speeds, the Doppler processor displays a dot for each object.each object.



• The vertical position represents the object’s velocity.



• When several objects move at the same velocity, the corresponding dot on the spectrum is brighter.brighter.


Doppler ProcessorDoppler ProcessorDoppler ProcessorDoppler Processor Color/DopplerColor/DopplerColor/DopplerColor/Doppler

Doppler InformationDoppler InformationDoppler InformationDoppler Information

Vel

ocity

There are 3 key pieces of information in a Doppler signal

Vel

ocity

In general, flow toward the transducer will be abov e the baseline, and flowaway from the transducer will be below the baseline .


Turbulence

There are 3 key pieces of information in a Doppler signal

Turbulence

Intensity

In general, flow toward the transducer will be abov e the baseline, and flowaway from the transducer will be below the baseline .

Doppler Shift EquationDoppler Shift Equation

2V ft Cos θ θ θ θc

fd =

fd = Frequency shift (ft-fr)ft = Transmitted frequency

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θ = θ = θ = θ = Angle of ultrasound beam withdirection of blood flow

V=velocity of blood flow


Doppler Shift EquationDoppler Shift Equation

Doppler.ppt WPS 2

Angle of ultrasound beam with

� It so happens that, for diagnostic ultrasound,the Doppler Shift lies in the audible range.

For example, if v = 0.5 m/s,

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For example, if v = 0.5 m/s,angle = 30 ° and c = 1540 m/s,

then fd = 2825 Hz(Between 20 Hz & 20 kHz)


It so happens that, for diagnostic ultrasound,the Doppler Shift lies in the audible range.

For example, if v = 0.5 m/s, f = 5 MHz,

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For example, if v = 0.5 m/s, fo = 5 MHz,angle = 30 ° and c = 1540 m/s,

= 2825 Hz(Between 20 Hz & 20 kHz)

Doppler AngleDoppler Angle

As Doppler angle


� As Doppler angleincreases, echoDoppler shiftfrequency decreases.(Pls note length of RedArrow)


Doppler AngleDoppler Angle

9090 80807070

6060

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5050

4040

3030

2020

1010

00

UltrasoundePulse Repetition Frequency

T T T T

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R R

Pulse RepetitionPeriod

* Pulse Repetition Frequency ( PRF transducer transmits a pulse.

* Pulse Repetition Frequency is dependent on trans mit depth and propagation velocity. ( 1540 m/s )


T T T T

R R

Pulse Repetition

PRF) is the number of times per second that

* Pulse Repetition Frequency is dependent on trans mit depth and propagation velocity. ( 1540 m/s )

Ultrasounde

Nyquist Limit

The maximum Doppler shif t velocity measurable in Pu lse Doppler is limited to onehalf the sampling rate def ined by the PRF, which is mainly determined by the sampling

27th January 2007 By : GEMS-A Marketing

half the sampling rate def ined by the PRF, which is mainly determined by the samplingdepth. For a given transducer and depth, this maxim um measurable velocity, which isknown as the Nyquist Limit , can be calculated using the following equation:

PRF Nyquist Limit = 2Remember:If the speed of the blood is faster than o ne-half of the PRF the signal will alias.


The maximum Doppler shif t velocity measurable in Pu lse Doppler is limited to onehalf the sampling rate def ined by the PRF, which is mainly determined by the sampling

January 2007 By : Mahendra Mehra

half the sampling rate def ined by the PRF, which is mainly determined by the samplingdepth. For a given transducer and depth, this maxim um measurable velocity, which is

, can be calculated using the following equation:

PRF

2 Remember:If the speed of the blood is faster than o ne-half of the PRF the signal will alias.

The Aliasing ProblemThe Aliasing ProblemThe Aliasing ProblemThe Aliasing Problem

• Pulsed Doppler has the limitation that the maximum velocity is determined by the sampling rate i.e. PRF, pulse repetition frequency.

• If the maximum velocity for that • If the maximum velocity for that transducer and depth exceeds the Nyquist limit, a phenomenon known as Aliasing occurs. Aliasing results in the display of wrong information with velocity display showing a wraparound effect.


Nyquist limit, a phenomenon known as

Doppler SummaryDoppler SummaryDoppler SummaryDoppler Summary

• Three Key Pieces of Information in a Doppler Signal– Velocity– Intensity– Turbulence

• In general, flow toward the transducer is above the baseline, transducer is above the baseline, flow away is below the baseline

• Major limitation is maximum velocity, which is based on frequency and sampling rate.

• 2nd limitation is the angle of flow relative to the transducer.


Three Key Pieces of Information in

transducer is above the baseline, transducer is above the baseline, flow away is below the baseline.

2nd limitation is the angle of flow

UltrasoundeContinuous Wave Doppler

Continuous Wave Doppler, or CW Doppler, is a simila r modality to Pulse Doppler in that frequencydata is gathered to determine blood velocity along the ultrasound line. With CW Doppler, the transmit and receive functions happen simultaneously. This o vercomes the maximum velocity limit, but the

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and receive functions happen simultaneously. This o vercomes the maximum velocity limit, but the exact point along the ultrasound line from which th e velocity data originated can not be determined.(No range resolution).

CW Doppler is used primarily in diagnosing abnormal ities in which range resolut ion is not importantor when the user is interested in the quantificatio n of high velocity jets.

CW PW

Range Resolution None Determined by Sample Volume Maximum Velocity Virtually Unl imited Lim ited by 1/2 PRF


Continuous Wave Doppler, or CW Doppler, is a simila r modality to Pulse Doppler in that frequencydata is gathered to determine blood velocity along the ultrasound line. With CW Doppler, the transmit and receive functions happen simultaneously. This o vercomes the maximum velocity limit, but the and receive functions happen simultaneously. This o vercomes the maximum velocity limit, but the exact point along the ultrasound line from which th e velocity data originated can not be determined.

CW Doppler is used primarily in diagnosing abnormal ities in which range resolut ion is not importantor when the user is interested in the quantificatio n of high velocity jets.

CW PW

Range Resolution None Determined by Sample Volume Maximum Velocity Virtually Unl imited Lim ited by 1/2 PRF

Continuous Wave DopplerContinuous Wave Doppler

Double Transducer

Transmit

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Continuous Wave DopplerContinuous Wave Doppler

Double Transducer

Transmit

Receive

Dopple r.ppt WPS 6

θθθθReceive

Color Flow Mapping

Color Flow Mapping (CFM) combines B-mode image format and Pulsed Doppler to provide a two dimensional representation of blood flow in

The Doppler ultrasound lines, like B-mode lines, are sequentially scanned through the frame. Multiple range gates are taken along the Doppler lines. The calculated velocity data is assigned a color to represent a certain velocity and direction, and then displayed combining with the B-mode image at the original location.

+BloodFlow 2 - D


mode image format and Pulsed Doppler to provide a two dimensional representation of blood flow in Real Time .

mode lines, are sequentially scanned through the frame. Multiple range gates are taken along the Doppler lines. The calculated velocity data is assigned a color to represent a certain velocity and direction, and then displayed

mode image at the original location.

= CFM

Color DopplerColor DopplerColor DopplerColor Doppler

• Color Doppler uses the same principals.

• The system acquires a Doppler Spectrum from many points in the image.

• For each point, the system determines the average velocity.

• The average velocity is converted to a color. Generally RED toward the transducer and BLUEaway.


Color DopplerColor DopplerColor DopplerColor Doppler

Color Doppler takes the averagevelocity and maps it to a color

...and then repeats the processthroughout the color flowregion.


Anatomy of a Color Flow ImageAnatomy of a Color Flow ImageAnatomy of a Color Flow ImageAnatomy of a Color Flow Image

• The result is an image with colors representing the average velocities.


General directionof ultrasound beam





This area is blue , soflow is generally awayfrom the beam, right to left



This area is red, so flow is toward the beam, left to right



This area is blue , soflow is generally awayfrom the beam, right to left

Color Flow has Doppler LimitationsColor Flow has Doppler LimitationsColor Flow has Doppler LimitationsColor Flow has Doppler Limitations Color/DopplerColor/DopplerColor/DopplerColor/Doppler

• Of the three pieces of information from a Doppler signal, CFM uses only the VELOCITY information. – Velocity– Intensity– Turbulence

• And has the same limitations:– Aliasing: Maximum velocity

limited by PRF– Dependent on angle of flow

The Angle ProblemThe Angle ProblemThe Angle ProblemThe Angle Problem Color/DopplerColor/DopplerColor/DopplerColor/Doppler

The Angle ProblemThe Angle ProblemThe Angle ProblemThe Angle Problem

• The transducer only sees a portion of the total velocity.


The transducer only sees a portion of the total velocity.


• On the other side, the apparent directioneven though the flow direction is the same!


direction appears to be opposite, even though the flow direction is the same!


• And in the center... there is NO apparent flow. Doppler processors cannot see flow perpendicular to the ultrasound beam.


And in the center... there is NO apparent flow. Doppler processors cannot see flow perpendicular to the ultrasound beam.

The Angle ProblemThe Angle ProblemThe Angle ProblemThe Angle Problem Color/DopplerColor/DopplerColor/DopplerColor/Doppler

Probe and Cursor Adjustments

Correct Doppler Shift



Probe and Cursor Adjustments

Correct Doppler Shift

Dopple r.ppt WPS 6

Incorrect Doppler Shift



Incorrect Doppler Shift

Doppler.ppt WPS 7

Note interior vessel wall (

or fatty streaking)


Carotid at 90Carotid at 90


Note interior vessel wall (intima

or fatty streaking)

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Carotid at 90Carotid at 9000



Flow DirectionFlow DirectionAmbiguityAmbiguity

Doppler.ppt WPS 9



ExcellentExcellentDoppler ShiftDoppler Shift

Doppler.ppt WPS 10



ExcellentExcellentDoppler ShiftDoppler Shift

Dopple r.ppt WPS 11

PRF 6000 Hz 37cm/sec

The Aliasing ProblemThe Aliasing ProblemThe Aliasing ProblemThe Aliasing Problem

PRF 3800 Hz 23 cm/sec


PRF 5000 Hz 31 cm/secPRF 5000 Hz 31 cm/sec

PRF 3000 Hz 19cm/sec

Dealing with the Doppler ProblemsDealing with the Doppler ProblemsDealing with the Doppler ProblemsDealing with the Doppler Problems

• What is going on here?• Why is the blood flow multi

red or all blue?


Why is the blood flow multi-colored, rather than all


• What is going on here?• Where is the flow velocity the highest?

A? B? C?

B

C


Where is the flow velocity the highest?

A

Dealing with the Doppler Problems

• What is going on here?• Where is the flow velocity the highest?

A? B? C?

The flow velocity is the same in the vessel, but th e angle makesit look like the blood is accelerating from A to B to C.

C

Color/DopplerColor/DopplerColor/DopplerColor/DopplerDealing with the Doppler Problems

Where is the flow velocity the highest?

The flow velocity is the same in the vessel, but th e angle makesit look like the blood is accelerating from A to B to C.

A

B


• What is going on here?• Why is the blood flow multi-colored, rather than all red or

all blue?


colored, rather than all red or


• What is going on here?• Why is the blood flow multi-colored, rather than all red or

all blue?

It’s a combination of changing angles and aliasing.


colored, rather than all red or

It’s a combination of changing angles and aliasing.


• Velocity asks “how fast is it going?”

• Velocity is subject to angle problems. Apparent velocity changes with angle.angle.

• Velocity is subject to aliasing. Depends on PRF.


• Intensity asks “ how manyare going?”

• Intensity is not subject to angle problems. How many doesn’t change with angle.angle.

• Intensity is not subject to aliasing. How many doesn’t change with sampling rate.


Vel

ocity

• Remember this?

• What if we used Intensity instead of information?


Turbulence

Intensity

instead of Velocity to map the flow


• The result is color flow that is not angle dependent, and not subject to aliasing.

• We call it Power Doppler Imaging (PDI).

• It appears to be more sensitive (no zero angle to worry about).


Thank YouRemember,,, enough “GAS”

solves all problems !!•G = GAIN•G = GAIN

•A = ANGLE

•S = STEERING


• Thank YouThank You

Remember,,, enough “GAS”solves all problems !!

Doppler Presentation

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