Principles of Doppler ultrasound

Principles of Doppler ultrasound

Samir Haffar M.D.Department of Internal Medicine

General principles

Spectral-specific parameters

Color-specific parameters

Power Doppler imaging

Normal flow in arteries

Normal flow in veins

Principles of Doppler ultrasound

General principles of Doppler ultrasound

Christian Doppler (1803 – 1853) Famous for what is called now the “Doppler effect”

1841 Professor of mathematics & physics Prague polytechnic

1842 Published his famous book “On the colored light of the binary stars & some other stars of the heavens”

1850 Head of institute of experimental physics Vienna University

Austrian physicist

The Doppler effectProposed by Christian Doppler in 1842

• Change in frequency of a wave for an observer movingrelative to the source of the wave

• Commonly heard when a vehicle sounding a sirenapproaches, passes, & recedes from an observer

• Received frequency Higher during approachIdentical at instant of passing byLower during recession

What is the Doppler phenomenon?

Thrush A, Hartshorne T. Peripheral vascular ultrasound: how, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

= ft

> ft

= ft

< ft

What is the Doppler phenomenon?

Doppler shift frequency (fd): ft – fr

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

ft

fr

Doppler equation

∆ F Doppler shift frequency (kHz)

F0 Ultrasound transmission frequency (MHz)

V Blood cell velocity (cm/sec)

Cos ӨCos of angle between US & flow direction

C Speed of sound in soft tissue (1 540 m/sec)

∆ F = 2 F0 V Cos Ө / C

Goals of Doppler

• Detection flow in a vessel

• Detection direction of flow

• Detection type of flow: Arterial or venous Normal or

abnormal

• Measurement the velocity of flow

Types of Doppler

Continuous wave Doppler

Spectral Doppler (duplex)

Spectral & color Doppler (triplex)

Power Doppler

All Doppler ultrasound examinations shouldbe performed with:

Tahmasebpour HR et al. RadioGraphics 2005 ; 25 : 1561 – 1575.

• Gray-scale US

• Color Doppler

• Spectral Doppler

• Power Doppler

Spectral-specific parameters

Spectral Doppler

Angle correctioncursor

Beam path

Sample volume

Baseline

EDV

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

PSV

Doppler shift frequency & angle of insonation

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Use of spectral baseline

Normal baseline

Inverted baseline

Dropping baseline

Sample volume length

Large sample volume lengthSmall sample volume length

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Optimizing gate size & position

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Wide gate including PV (above baseline) & HV (below baseline)

Gate should be positioned over central part of the studied vessel

Doppler equation

∆ F Doppler shift frequency (kHz)

F0 Ultrasound transmission frequency (MHz)

V Blood cell velocity (cm/sec)

Cos ӨCos of angle between US & flow direction

C Speed of sound in soft tissue (1 540 m/sec)

∆ F = 2 F0 V Cos Ө / C

Percentage error in velocity measurements & angle of insonation

In order to minimize this error,angles of insonation > 60% should not be used

Optimizing Doppler angle Larger the angle, greater the error

• Ideally should be zero Usually not possible • Smallest angle possible Not under our control• Do not use angle > 60° Great error in velocity• Angle 90° Complete loss of flow

• Transducer position Obtain smaller angle

• Different US systems May be different results

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Doppler angle measurement

Angle: 60°PSV: 110 cm/secEDV: 41 cm/sec

Angle: 44°PSV: 74 cm/secEDV: 27 cm/sec

Thrush A et al. Peripheral vascular ultrasound. Elsevier Churchill Livingstone, London, 2005.

Changing position of the transducer

IntercostalTransabdominal Subcostal

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Adjusting spectral velocity scale

Spectral scale: 200 cm/sec Spectral scale: 50 cm/sec

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Color Doppler image, color bar, & color scale unchanged Spectral component is active

Adjusting spectral Doppler gain Gain setting 0% Gain setting 38%

Gain setting 77% Gain setting 100%

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Spectral wall filter

Wall filter 75 Hz

Wall thump removed

Wall filter 550 Hz

Filter frequency too high

Altered waveform

Wall filter 50 Hz

Wall thump

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Spectral aliasing CCA

Dropping baseline Increasing scalePeaks cross baseline

Rubens DJ et al. Doppler artifacts & pitfalls. Ultrasound Clin 2006 ; 1 : 79 – 109.

Color-specific parameters

Color map

BaselineWall filter

Changing color baseline

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

When color baseline changed → color velocity range changed

Range of depicted velocities remains constant

Examples of different color maps

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Velocity range(cm/sec)

Inversion ofcolor map

Color writepriority

Baselinewall filter

Inversion of color flow

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Reversal of this inversionAppropriate directional flow noted

Portal venous flow appears blueFalsely suggests flow reversal

Inversion of spectral flow

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Color box size / Overlay

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Oversized color box↑ frame rate & ↓ resolution

Reduced color box size↓ frame rate & ↑ resolution

Color box should be as small & superficial as possible

Doppler angle effects

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Color box steeringChanging angle of insonation

Large angleUnusable image

Small angleGood image

Moderate angleFlow is not optimal

Steered either left or right by a maximum of 20 – 25° Sensitivity of transducer decreases as beam is steered

Thrush A et al. Peripheral vascular ultrasound. Elsevier Churchill Livingstone, 2nd edition, 2005.

Color box steered in more than one direction to demonstrate flow in the whole vessel

Color box steering

Thrush A et al. Peripheral vascular ultrasound. Elsevier Churchill Livingstone, 2nd edition, 2005.

Adjusting color velocity scale

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Color velocity scale 2 cm/secColor aliasing in PV & its branches

High color velocity scale (69 cm/sec)Apparent absence of flow in PV

Color velocity scale 30 cm/sec Normal flow in a patent PV

Color Doppler aliasing

Velocity scale range 12 cm/sec Velocity scale range 23 cm/sec

Rubens DJ et al. Doppler artifacts & pitfalls. Ultrasound Clin 2006 ; 1 : 79 – 109.

Portal vein pseudo-clot

Velocity scale: 20 cm/s Velocity scale: 7 cm/s

Adjusting color gain

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Color gain should be set as high as possible without displaying random color speckles

Color gain 44% Color gain 65% Color gain 100%

Adjusting color gain

Flow ‘bleeding out’ of the vesselColor gain set too high

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Adjusting color wall filter

Filter setting displayed on color scale (horizontal arrow)

Filter too high Removing low flow

Filter setting reduced Display low flow

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Pseudo-thrombosis of main PV Adjusting velocity & angle of insonation

Velocity: 24 cm/secWall filter: medium

Angle 90°

Velocity: 7 cm/secWall filter: medium

Angle < 90°

Radiol Clin N Am 2006 ; 44 : 805 – 835.

Doppler panel on console of many contemporary US imagers

Each parameter can be adjusted to optimize spectral or

color Doppler components of the examination

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Clinical & tissue-specific presets

• Clinical option GeneralAdultObstetric (etc…)

• Tissue-specific preset AbdomenRenalTransplant (etc...)

Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675.

Once a transducer selected

preset choices includes:

Guidelines for optimal Doppler examination

Adjust gain & filter

Adjust velocity scale & baseline

Doppler angle < 60° by steering & probe position

Color box as small & superficial as possible

Sample volume size: 2/3 of vessel width in the center

Avoid transducer motion

Rubens DJ et al. Doppler artifacts & pitfalls. Ultrasound Clin 2006 ; 1 : 79 – 109.

Power Doppler imaging

Advantages of power mode Doppler

• No aliasing

• Angle independent

• Increased sensitivity to detect low-velocity flow Distinguish pre-occlusive from occlusive lesionsSuperior depiction of plaque surface morphology

• Useful in imaging tortuous vessels

• Increases accuracy of grading stenosis

Power Doppler imaging

Large plaque ulcerICA

Narrow flow channel in ICA“string sign” or “trickle flow ”

Disadvantages of power Doppler imaging

• Do not provide velocity of flow

• Do not provide direction of flowNew machines provide direction of flow in power mode

• Very motion sensitive (poor temporal resolution)Less suitable for rapid scan along vessels

Normal flow in arteries & veins

Flow at a curvature & bifurcation

Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004.

Apex of parabola moves away from concave wall at a curve

Apex of parabola moves away from outer wall at bifurcation

Flow around curves in a vessel

Tortuous ICA

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

A B

A

PSV outside the bend 70 cm/sec

B

PSV inside the bend 55 cm/sec

Normal flow reversal zone in ICA

Opposite to origin of the ECAHigh velocities near flow divider

Reversal on opposite side to flow divider

Thrush A et al. Peripheral vascular ultrasound. Elsevier Churchill Livingstone, London, 2005.

High & low resistance arterial flow

High-resistance flowSFA

Low-resistance flowICA

Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004.

Arterial high resistance flow

Typical normal Doppler spectra

Normal anterior tibial arteryTriphasic flow

Pulsatility index

Most commonly used of all indices

S Systolic

D Minimum diastolic

M Mean

PI S – D / M

Effect of exercise on flow

Dorsalis Pedis Artery at restTriphasic flow

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

DPA following exerciseMonophasic hyperemic flow

Arterial monophasic flow

• HyperemicExercise Infection Temporary arterial occlusion by blood pressure cuff

• Distal to severe stenosis or occlusion Low velocity Longer rise time* Tardus-Parvus wave

* Rise time: time between beginning of systole & peak systole

Tardus-Parvus waveDistal to severe stenosis or occlusion

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Tardus: Longer rise time

Parvus: Low PSV

Arterial low resistance flowTypical normal Doppler spectra

Normal internal carotid artery

Pourcelot’s resistance index

RI S – ED / S

Normal 50 – 70 %

Abnormal > 80 %

Accleration Time (AT) or Rise Time (RT)

• Length of time in seconds from

onset of systole to peak systole

• Normal value: ≤ 0.07 second

Acceleration index

AI = X (KHz)

Probe frequency (MHz)

Normal value: > 3.8 cm/s2

Aacleration time & PSV

Early systolic pick

AJR - Dec 1995

Biphasic with late systolic pick

Monophasic with late systolic pick

AT & AI according to degree of stenosis

Moderate stenosis 50 – 85%

Normal Severe stenosis> 85 %

Measurement of volume flow

Volume = Cross-sectional area × Mean velocity × 60 (ml/min) (cm2) (cm/sec)

Cross-sectional area (cm2): π d2 / 4d: diameter

Doppler equationConverting Doppler shift frequency to velocity

∆ F Doppler shift frequency (kHz)

F0 Ultrasound transmission frequency (MHz)

V Blood cell velocity (cm/sec)

Cos ӨCos of angle between US & flow direction

C Speed of sound in soft tissue (1 540 m/sec)

∆ F = 2 F0 V Cos Ө / C

∆ F

F0

V ?

Cos Ө

C

∆ F = 2 F0 V Cos Ө / C

50 cm/s

1.6 kHz

5 MHz

60°

1 540 m/sec

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Doppler equationConverting Doppler shift frequency to velocity

Blood flow & PSV changes relatedto severity of arterial stenosis

Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004.

Flow through a stenosis

Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when.Elsevier Churchill Livingstone, London, 2nd edition, 2005.

Increased velocity through stenosis Flow reversal beyond stenosis

CCA

IJV

ICA

Color from red to turquoise Posterior wall – deep blue

Pic Systolic Velocity ratio

Robbin ML et al. Ultrasound Clin 2006 ; 1 : 111 – 131.

Proximal: 2 cm proximal to stenosis

Same Doppler angle if possible

Post-stenotic zone/Spectral broadeningProportional to severity of stenosis

• Cannot be precisely quantified (evaluated visually)Fill-in of spectral window > 50% diameter reductionSeverely disturbed flow > 70% diameter reduction

High amplitude & low frequency signalLow amplitude & high frequency signalFlow reversal – Poor definition of spectral

border

• May be only sign of stenosis: calcified plaque

Spectral broadeningImmediate post-stenotic zone

Pseudospectral broadening

• High gain setting

• Vessel wall motion

• Site of branching

• Abrupt change in vessel diameter

• ↑ velocity: athlete, high cardiac output, AVF1, & AVM2

• Tortuous vessels

• Aneurysm, dissection, & FMD3

1AVF: Arterio-Venous Fistula2AVM: Arterio-Venous Malformation3FMD: Fibro-Muscular Dysplasia

Color Doppler bruit

Extensive soft tisuue color Doppler bruit surrounds

the carotid bifurcation with 90% ICA stenosis

Venous valve

Two cups of a valve clearly seenIt is uncommon to see venous valves with this clarity

Normal venous flow

Spontaneity Spontaneous flow without augmentation

Phasicity Flow changes with respiration

Compression Transverse plane

Augmentation Compression distal to site of examination Patency below site of examination

Valsalva Deep breath, strain while holding breath Patency of abdominal & pelvic veins

Normal venous flow

Spontaneity Spontaneous flow without augmentation

Phasicity Flow changes with respiration

Compression Transverse plane

Augmentation Compression distal to site of examination Patency below site of examination

Valsalva Deep breath, strain while holding breath Patency of abdominal & pelvic veins

Phasicity

Flow changes with respiration

Slow ApneaRapid

Normal venous flow

Spontaneity Spontaneous flow without augmentation

Phasicity Flow changes with respiration

Compression Transverse plane

Augmentation Compression distal to site of examination Patency below site of examination

Valsalva Deep breath, strain while holding breath Patency of abdominal & pelvic veins

Compressibility of veins

Do not press too hard since the normal vein collapsesvery easily making it difficult to find

11

Incompressibility = Thrombus

Do not compress vein more than necessary in recent thrombusFear of detaching thrombus to cause PE

Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004.

External compression of the vein

Relaxation Compression

A

Normal venous flow

Spontaneity Spontaneous flow without augmentation

Phasicity Flow changes with respiration

Compression Transverse plane

Augmentation Compression distal to site of examination Patency below site of examination

Valsalva Deep breath, strain while holding breath Patency of abdominal & pelvic veins

Augmented flow in popliteal vein

Aug Competent vein

Normal venous flow

Spontaneity Spontaneous flow without augmentation

Phasicity Flow changes with respiration

Compression Transverse plane

Augmentation Compression distal to site of examination Patency below site of examination

Valsalva Deep breath, strain while holding breath Patency of abdominal & pelvic veins

Valsalva’s maneuver

Valsalva’s maneuver

A V

Normal respiration

A V

Valsalva maneuver

Start Valsalva

End Valsalva

Competent vein

Indicate on the report whether

the examination was excellent, good or poor

Emphasize if a scan is suboptimal

Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004.

References

Arnold – 2004 Elsevier – 2005 Elsevier Mosby – 2005

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