Principles of Doppler ultrasound

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 effect Proposed by Christian Doppler in 1842 • Change in frequency of a wave for an observer moving relative to the source of the wave • Commonly heard when a vehicle sounding a siren approaches, passes, & recedes from an observer • Received frequency Higher during approach Identical at instant of passing by Lower 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 Ө Cos 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 should be 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 correction cursor 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 Ө Cos 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/sec EDV: 41 cm/sec Angle: 44 PSV: 74 cm/sec EDV: 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 Baseline Wall 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 of color map Color write priority Baseline wall filter
Inversion of color flow Kruskal JB et al.RadioGraphics 2004 ; 24 : 657 – 675. Reversal of this inversion Appropriate directional flow noted Portal venous flow appears blue Falsely 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 steering Changing angle of insonation Large angle Unusable image Small angle Good image Moderate angle Flow 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/sec Color 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 vessel Color 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/sec Wall filter: medium Angle 90 Velocity: 7 cm/sec Wall 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 General Adult Obstetric (etc…) • Tissue-specific preset Abdomen Renal Transplant (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 lesions Superior depiction of plaque surface morphology • Useful in imaging tortuous vessels • Increases accuracy of grading stenosis
Power Doppler imaging Large plaque ulcer ICA 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 flow New 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 flow SFA Low-resistance flow ICA 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 rest Triphasic flow Thrush A, Hartshorne T. Peripheral vascular ultrasound: How, why and when. Elsevier Churchill Livingstone, London, 2nd edition, 2005. DPA following exercise Monophasic hyperemic flow
Arterial monophasic flow • Hyperemic Exercise 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 wave Distal 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 flow Typical 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 / 4 d: diameter
Doppler equation Converting Doppler shift frequency to velocity ∆ F Doppler shift frequency (kHz) F0 Ultrasound transmission frequency (MHz) V Blood cell velocity (cm/sec) Cos Ө Cos 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 equation Converting Doppler shift frequency to velocity
Blood flow & PSV changes related to 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 broadening Proportional to severity of stenosis • Cannot be precisely quantified (evaluated visually) Fill-in of spectral window > 50% diameter reduction Severely disturbed flow > 70% diameter reduction High amplitude & low frequency signal Low amplitude & high frequency signal Flow reversal – Poor definition of spectral border • May be only sign of stenosis: calcified plaque
Spectral broadening Immediate 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 Fistula 2AVM: Arterio-Venous Malformation 3FMD: 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 seen It 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
Phasicity Flow changes with respiration Slow ApneaRapid
Compressibility of veins Do not press too hard since the normal vein collapses very easily making it difficult to find11
Incompressibility = Thrombus Do not compress vein more than necessary in recent thrombus Fear 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
Augmented flow in popliteal vein Aug Competent vein
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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