Basic Doppler

GE Medical SystemsUltrasound

LOGIQ LOGIQ LineLine

Welcome toWelcome to

TheThe Basics Basics ofofDoppler UltrasoundDoppler Ultrasound



„ About the Colorlightning of the Dopplerstars“ 1842 Johann Christian Doppler

The Doppler Effect

stated that any directional motion between a light source and an observer would produce a detectable frequency shift or color change (“twinkling” of stars) Doppler’s theory is applicable to both light and sound



Doppler EffectIn ultrasound Imaging, echoes received from most tissues will be at the same frequency as the transmitted beam. However, if echoes received are from tissues or blood cells that are moving, the transmitted 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 velocity of the moving object. Additionally, movement toward the transducer results in a higher received frequency, and movement away in a lower received frequency.



Index of Slides:Index of Slides:The Dopper Effect Applied to Sound 4-10

Doppler Ultrasound Modes 11-17

Duplex/Triplex 18

Pulse Repetition Frequency 19

Aliasing 20-23

Adjusting the Doppler Spectrum 24,25

Automatic Spectrum Optimization 26

CFM Adjustments 27

Artifacts 28

Hemodynamics 29

Spectral Doppler Waveforms 30-33

Doppler Calculations 34

Auto Doppler Calcs. 35

Hints and Tips 36-37



The Doppler Effect applied to sound

The sound frequency from an approaching source is higher than from one receding

The difference is the Doppler shift frequency - fD



The Doppler Equation

fD : 2f x Vx cosØ/c

•f: the insonating frequency, in MHz

•V: the velocity of the blood flow

•Ø: the insonating angle (angle of observation)

•c: the speed of sound through soft tissue

(ca. 1540m/sec.)

fD is kHz, which is within the audible range



Angle of Observation



Angle of Incidence

When the motion of the object and the transmittedbeam are not parallel, it is necessary to correct for the angular difference. Motion that occurs at an angle to the beam axis will result in a decreasein the magnitude of the frequency shift and a lowercalculated velocity. Therefore, the transmitted beam needs to be parallel to the flow for the most accurate velocity. An equation is used to correct for the angle offset. The transducer receives only the componentparallel to the beam Vcos .

Ultrasound Beam

Blood FlowV



The smaller the angle between the insonated vessel and the probe, the higher is the Doppler shift.



The Insonating Frequency, The Insonating Frequency, ff

• In combined modes the probe sends two different sets of frequencies: one for B-mode, one for Doppler mode(s)

• According to the Doppler equation f should be as high as possible. • But as the reflectors, the red blood cells, are very small, their echoes

are rather weak.• Because low frequencies travel farther than high ones a reatively low f

is used for Doppler modes.

B- mode frequency-

Doppler frequecies

The LOGIQ systems have for CFM og PDI two different D-frequencies in all probes, and are programmed to use the lower one



Doppler modesDoppler modes

PW: Pulsed Wave Doppler (Spectral Doppler)

CFM: Color Flow Mapping (Color Doppler)

PDI: Power Doppler Imaging (Power Doppler)

CW: Continuous Wave Doppler (Spectral Doppler)



Clinical use of the Doppler EffectClinical use of the Doppler Effect

Quantification of flow velocities and indicesPWD, CW

Presence of flow, vascular or cystic

CFM, PWD, PDI

The direction of flow in respect to the probein respect to the probe

CFM , PWD, CW



Spectral Doppler

Spectral Doppler, of high value in ultrasound diagnosis, can be used for evaluation of blood flow, includes three kinds:

- Pulse Doppler(PW) - High Pulse Repetition Frequency Pulse Doppler (HPRF) - Continuous Wave Doppler (CW).



Pulse Ultrasound

For practical use, most modern ultrasound systems are designed based on the principle of pulse-echo technique, which means that transducer emits only a few cycles of pulses at a time into the human body. When encountering tissues interfaces, reflection and scattering will occur and produce pulse echoes, By detecting these echoes, tissue positioning and identification as well as diagnosis can be made.



Pulse Doppler

Transducer

Pulsed Doppler Line

In Pulse Doppler, a single ultrasound lineis repeatedly fired. Echoes reflected from moving structure, including blood cells, experience a Doppler shift in frequency.Using the Doppler equation, the echo information obtained within the Sample Volume is analyzed for shifted frequency content and amplitude, rather than transmitfrequency amplitude. From this, the bloodvelocity can be determined.

SampleVolume



Pulse Doppler

Time

Velocity

In order to obtain enough data to calculate the frequency componentsof the sampled volume, many ultrasound lines must be fired.

The frequency data is converted to velocity, and displayed in a scrollingstrip format on the monitor.

The highest detectable velocity islimited by one half of the rate at which the ultrasound lines are fired, known as *Nyquist Limit “.



Pulsed Doppler (Spectral Doppler, PW)

Is a graphic representation of velocity and profile of the flow inside the Sample Volume, SV as a function of time

Flow toward the probe is seen above the Baseline

Flow away from the probe below the Baseline



Pulse Repetition Frequency T T T T

R R R R

Pulse RepetitionPeriod

* Pulse Repetition Frequency (PRF) is the number of times per second that transducer transmits a pulse.

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



Pulse Repetition Frequency (PRF)Pulse Repetition Frequency (PRF)

PRF is the frequency of pulses transmitted by the probe.The higher the flow velocity, the higher the PRF settings must be

PRF=2x fD is optimalPRF can be shown as kHz or cm/sec.

CFM PRF

PWD PRF



Pulsed Doppler (PW)

For Pulsed Doppler the probe uses only one crystal, which acts as both transmitter and receiver.

A timing switch activates a window in the region of interest - the Sample Volume (SV)

Transmitt Receive

Time gate Signal processing

Delay

Time

Time



Frequency Spectrum-Analysis

For each received signal a Doppler shift is calculated.

The frequencies/velocities are displayed as bright dots

Each frequency/velocity is translated into a seperate Doppler curve, all curves together are combined to form the DOPPLER SPECTRUM where the frequencies/velocities are assigned different dot brightness or color.



Continuous Wave Doppler

Continuous Wave Doppler, or CW Doppler, is a similar 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 overcomes the maximum velocity limit, but the exact point along the ultrasound line from which the velocity data originated can not be determined.(No range resolution).

CW Doppler is used primarily in diagnosing abnormalities in which range resolution is not importantor when the sonographer is interested in the quantification of high velocity jets.

CW PW

Range Resolution None Determined by Sample Volume Maximum Velocity Virtually Unlimited Limited by 1/2 PRF



Continuous Wave Doppler

Time

Velocity

Transducer

Monitor



Continuous Wave Doppler: (Unidirectional)

The result of the Doppler shift will increase or decrease, depending of the blood flow direction

Vessel Skin



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 Real Time.

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 displayedcombining with the B-mode image at the original location.

+ =Blood Flow 2 - D CFM



MTI (Moving Target Indicator)

Blood Cell

Blood Cell

Ultrasound Line

Ultrasound Line

First

Second

Subduction Blood Cell Signal



Limitations of CFM

- Only give the average of the velocity across the beam, can not get the maximum velocity.- Sensitivity, a compromise to be made among the depth, velocity range, and PRF- Frame Rate, influenced by FOV , scan angle and control system of transmit and receive.



CFM Display

Transducer

Doppler Ultrasound Line

Color Box

Monitor



CFM, Color DopplerCFM, Color Doppler

Color coded Doppler signals from numerous small sample volumes insidethe Region Of Interest (ROI)Color coding is assingned according to flow direction in respect to theprobe, and mean velocities

Flow toward the probe is coded RED

Flow away from probe is coded BLUE

High velocities have bright hues, low velocities dark hues



No frequency spectrum is displayed, color information is superimposed on the 2D image.

CFM, Color Doppler

The wider the Region of Interest (ROI,color box)>the higher number of color lines>the more time needed to create each image frame>the lower the Frame Rate



PDI, Power Doppler

Color coded signals from numerous small Sample Volumes inside theRegion Of Interest (ROI, color box)

Color coding is assigned according to flow intensities, (power), notdirection.

Is used to detect flow in very small, or low flow vessels



Duplex / TriplexDuplex / Triplex

Duplex: Duplex: B mode og Doppler spectrumB mode og Doppler spectrumIs the fastest to generate Is the fastest to generate

Triplex: B mode, CFM and Doppler spectrum

Simultaneous Triplex: B, CFM and PW live at the same time

takes longer time to generate

Alternating Triplex: B/CFM mode and Doppler spectrum live in turns - switch between them by pressing B-Pause



Nyquist Limit

The maximum Doppler shift velocity measurable in Pulse Doppler is limited to onehalf the sampling rate defined by the PRF, which is mainly determined by the samplingdepth. For a given transducer and depth, this maximum measurable velocity, which isknown as the Nyquist Limit, can be calculated using the following equation:

PRF Nyquist Limit = 2



Aliasing

If the maximum velocity for that transducer and depth exceeds the Nyquist limit, aphenomenon known as Aliasing occurs. Aliasing results in the display of erroneousvelocity information.(Showing a “wraparound” effect.)

Velocity

2

0

-2

Spectral Display Showing Aliasing



AliasingAliasing

The aliasing phenomenon is seen in old movies, where wagon wheelsappear to rotate slowly backwards instead of fast forwards.

The true velocity and correct direction of the wheel is only seen if themovie frame rate is frequent enough to detect the position of the wheel ateach quarter turn.

The moving wheel is filmed every quarter turn: no aliasing

Aliasing occurs because the wheel is only filmed every three quarter turn: it appears to move slowly backwards



AliasingAliasing

Doppler Aliasing is a result of too low PRF settingsCan also be called undersampling: The flow velocity is higher than the PRF, the probe reads part of the flow as negative flowAliasing is compensated by:1. Increasing PRF2. Lowering the Baseline



Spectral AliasingSpectral Aliasing

On the frequency spectrum display the aliasing effect is represented by a curve where the top is transposed to the negative range



HPRF Doppler

The Nyquist limit will decrease with depth of the sample volume. As this limit reaches 1/2 PRF, the system automatically increases the sample rate by increasing the PRF and the number of samples. This results in more than one wavefront propagating through the body simultaneously. Therefore, information obtained may be from more than one location.

Transducer



Color AliasingColor Aliasing

A mix of red and blue color signals is seen.

Red changes to Blue through White: a classical sign of CFM aliasing



Adjusting the Spectrum

Angle of insonation: adjust Angle Steer or slightly angle the probe

Angle Correct: align crosshair inside SV in parallelto the vessel walls/blood flow

PRF: adjust according to flow velocity

Baseline: the whole spectrum should beshown above or below the Baseline



Adjusting the Spectrum

Sample Volume: keep SV size inside the vessel lumen

Gain: is set correctly when background noise is only just discernable

Wall Filter: adjustment is rarely needed, WF is linked to PRF

Sweep Speed: low Sweep Speed to show many cycles in timelinefast Sweep Speed for better detail of cycle(s)



SmartScanSmartScan::One-Touch Auto One-Touch Auto Spectral Spectral OptimizationOptimization (ASO) (ASO)

ASO adjustments: •PRF (up to 3 iterations)

•Baseline Shift

•Angle correct (optional)

•Invert (optional)



CFM AdjustmentsPRF• low PRF for slow flows/small vessels - if PRF is too high, low flows are not detected

• high PRF for high flow velocities to avoid color overwriting of tissue/ vessel walls and aliasing

Gain

Gain and PRF should be adjusted together

• higher Gain for small vessels

• decrease Gain to avoid overwriting of tissue/vessel walls

Angle Steer (linear probes)

ROI should be angled toward the flow direction



ArtifactsArtifacts

Ghost-artifact of the Dopplerspectrum, appears when theangle of insonation is close to90 degrees

Angle artifact in CFM, appears when the angle of insonation is close to 90 degrees.Appearance is different from alaising: Red and Blue are separated by BlackBlack



Hemodynamics

Plug flow Laminar flow(parabolic)

Turbulent flow - speed

Turbulent flow at a stenosis

At a stenosis: spectral broadening proximal to the stenosis high velocities at the narrowest point, complete spectral broadening and flow on both sides of the Baseline caused by eddy currents and vortices distal to the stenosis

Plug flow: most of the reflectors travel at the same velocity >narrow spectral waveform

Laminar flow: the reflectors in mid-stream travel at higher velocities, especially duing diastole >broader spectral waveform

Turbulent flow: the reflectors travel at different velocities >spectral broadening



Spectral Doppler waveformsSpectral Doppler waveformsDoppler arterial waveforms are affected by:• Cardiac contractility• The resistance in the receiving bed• Compliance of the vessel walls• Turbulence• Viscosity of the blood

and vary in accordance with the cardiac cycle

Doppler waveforms are used for:

1. Measuring velocities- for exmple to quantify stenoses

These measurements are angle depentant for accuracy: the insonating angle must not exeed 60 degrees

2. Indices- for example PI or RI,

which do not depend on the angle for accuracy of measurement, but the Doppler Equation must be kept in mind



High/Low Resistance Arterial WaveformsHigh/Low Resistance Arterial Waveforms

There are two major arterial waveforms:

High peak systolic flow, low, absent or negative

flow in diastole

High resistance waveform is mostly seen in arteries supplying muscles and skin,

which in resting phase have high resistance to the blood flow.



High/Low Resistance Arterial WaveformsHigh/Low Resistance Arterial Waveforms

Low resistance waveform Low resistance waveform is typical for arteries supplying blood hungryis typical for arteries supplying blood hungryorgans such as kidneys and brain. The vessels act like slack funnelsorgans such as kidneys and brain. The vessels act like slack funnelssupplying the receiving bed with rich perfusion.supplying the receiving bed with rich perfusion.

Flow above the baseline troughout the carciac cycle,

the lower the resistance in the receiving bed, the higher the diastolic flow



The arterail waveforms change according to The arterail waveforms change according to the peripheral resistancethe peripheral resistance..

Radial artery in rest phase: Radial artery in rest phase: high peak systolic flow, low orhigh peak systolic flow, low ornegative diastolic flow negative diastolic flow

After moving the fingers the After moving the fingers the waveform changes according to the waveform changes according to the altered peripheral resistancealtered peripheral resistance



Doppler calculationsDoppler calculations

RI (Resistance Index):PsV-EdV/PsV

PI (Pulsatility PI (Pulsatility Index):Index):PsV-EdV/TAMAXPsV-EdV/TAMAX Peak

systolic Velocity

EnddiastolicVelocity

Time Average MAX curve

Frequently used Frequently used measurements/ indices:measurements/ indices:

PsVPsVEdV EdV

ACCel (Acceleration ACCel (Acceleration Index)Index)



Auto Doppler Calcs.Auto Doppler Calcs.

Auto calcs. save examination time and are operator independent.

Measurements of velocities and calculation of indices can be performedmanually or automatically on the spectrum live or frozen.

Six Sigma for Healthcare Project, July 2003:Auto calcs. and ASO for third trimester flow exams and measurement of PI in the umbilical artery reduce average Doppler exam time by 45%.



Hints and Tips

TrueAccess:In the frozen or stored image you can adjust several parameters

Angle Correct

Change Sweep Speed Shift Baseline

Adjust Gain



Hints and Tips L3Hints and Tips L3

If simultaneous triplex is too slow:If simultaneous triplex is too slow:1. Zoom the image around the SV1. Zoom the image around the SV2. Switch to Alternating Triplex, 2. Switch to Alternating Triplex, (Sub menu, Pg.2, / Dupelx/Triplex OFF)(Sub menu, Pg.2, / Dupelx/Triplex OFF)3. Switch to Duplex 3. Switch to Duplex

For PI and TAMAX, if the Auto TAMAX curve is inaccurate:For PI and TAMAX, if the Auto TAMAX curve is inaccurate:Switch to Manual Trace Switch to Manual Trace (Top Menu)(Top Menu) click the calc.of choice from the click the calc.of choice from the Measurement menu, i.e. PI, place the cursor at the Start Systolic point of a , i.e. PI, place the cursor at the Start Systolic point of a cycle, manually trace the spectrum to the End Diastolic point, press SET. cycle, manually trace the spectrum to the End Diastolic point, press SET.



Thank you...

Basic Doppler

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