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Vascular Ultrasound: Physics and Haemodynamics

• “Doppler” principles

• Spectral Waveform

• Key factors

• Haemodynamics: Stenosis

• Waveforms

• Image recognition

Objectives

• “Vascular Ultrasound”

• Ultrasound of blood vessels

• Arteries / Venous

• Don’t exist in isolation

• Attached to systems

• Own pathology

• Change with pathology

• Advanced Ultrasound

• Should be learned early

• Carotid

Vascular Ultrasound: A flawed paradigm

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The Doppler Effect

What is the Doppler Effect

What is the Doppler Effect?: More Familiar The Stationary Ambulance

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The Moving Ambulance

• B-mode

• Colour

• Spectral

Ultrasound: ComponentsChristian Doppler (1803-53)

The Doppler Effect

• Movement

• Change in sound wavelength/ frequency

• Relationship to Ultrasound

The Doppler Effect

?Back to the basics

“observed frequency of a wave

depends on the relative speed of the

source and the observer”

• Radar/Sonar

B-mode: The Basics

Ultrasound B-mode: The Basics… Ultrasound B-mode: The Basics…

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• Variation in Anatomical Reflectors

Ultrasound B-mode: The Basics…

• Ultrasound (MHz)

• Frequency

• Time

• Image

B-mode: The Basics…

• B-mode

• Same Frequency

• Doppler

• Change in frequency

• Visualise movement

Doppler: Ultrasound

• Represent the “change in frequency”

• Spectral

• Fast Fourier Analysis

• Colour

• Autocorrelation

• Sound

Doppler: Ultrasound

• Colour Duplex Ultrasound

• What determines the change in frequency?

Doppler: Ultrasound What determines the change in frequency?

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What determines the change in frequency?

Change in frequency =2 X Reflector Speed X Angle (Cos 0)

Speed of Sound

X Freq

Doppler: The Equation

http://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-html/chapter_01.htm

Using the Doppler equation: Explain

• B-mode

• Doppler

• Colour

• Colour flow imaging

• Colour Doppler

• Amplitude Doppler

• Spectral Doppler

• Duplex Ultrasound

• Colour duplex ultrasound

Doppler: Terminology

• Autocorrelation

• Qualitative

• Directional

• Directs interrogation

• Optimise

• Spatial resolution

• Temporal resolution

• Contrast resolution

• Own range of settings- Name them

Doppler: Let’s look at Colour

• Optimize B-Mode image first

• Keep box small

• Width

• Create a good Doppler angle

• Heel / toe probe or steer

• PRF / Scale

• Set color gain appropriately

Color Flow Imaging: Optimisation

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• Fast Fourier Trans.

• Mathematical tool

• Frequency information

• Spectral waveform

Spectral Doppler

• Own settings- Name them

Spectral Doppler

Spectral: The Waveform

Moment in time

Range of V’s

Intensity

Spectral: The Waveform

• PSV

• EDV

• Ratios…

• Resistance

• Mono, Bi, Triphasic

• Calculation (S/D, RI, PI)

• Blood Flow Profile

• Where are these useful?

Spectral: Information

• PSV

• EDV

• Ratios…

• Resistance

• Mono, Bi, Triphasic

• Calculation (S/D, RI, PI)

• Blood Flow Profile

• How to understand

• Pipes , hoses, basic plumbing…

Spectral: Information

Basic Haemodynamics

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• Stenosis

• Increase in velocity

Spectral: PSV

• How is PSV explained

• Preservation of Energy

• (Fluid Energy)x = Pressure & Kinetic E.

Spectral: Stenosis: “Mr Benoulli”

x x

What is a critical stenosis?

• Loss of Pressure/ Energy

• Carotid (55-65% diameter)

• Iliac A (97% area)

What is a critical stenosis?

x x - y

• Reduction in volume/pressure

• Renal Artery: 82% area

• RA Diameter: 60-70%

• Excretion of renin… ?

Critical Stenosis

• Severe stenosis

• Increase in EDV

• Why?

Spectral: EDV/ Ratios

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• Severe stenosis

• Increase in EDV

• Loss volume

• Less resistance

• Distal vasodilation

• … take us to

Spectral: EDV/ Ratios

• Cardiac Output

• Artery

• tortuosity

• compliance

• no. of branches

• size

• Distal Vascular Bed

Spectral: Resistance

• Pressure Difference

• Q= Flow/Volume

• n = Viscosity

• r = Radius of the Vessel

Spectral: Resistance: “Mr Poiseuille”

• Pressure Difference

• Q= Flow/Volume

• n = Viscosity

• r = Radius of the Vessel

• If r = .0001m

r4 =.00000000000000001

Spectral: Resistance: “Mr Poiseuille”

Contributions to ResistanceAor ta

4%

Ar ter i ol es

41 %

Capi l l ar i es

27%

Venous

7%

M ai n Br anches

1 0%

Lar ge Ar ter i es

5%

T er mi nal B r anches

6%

Aorta

Large Arteries

Main Branches

Terminal Branches

Arterioles

Capillaries

Venous

Spectral: Resistance contributions

• Draw waveforms

• Monophasic

• Biphasic

• Triphasic

• Label high/ low resistance

Spectral: Resistance Waveforms

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• Draw waveforms

• Monophasic

• Biphasic

• Triphasic

• Label high/ low resistance

Spectral: Resistance Waveforms

• ICA

• CCA

• ECA

• Vertebral

• Subclavian

Spectral: The Carotid

• ICA

• CCA

• ECA

• Vertebral

• Subclavian

• ? Hepatic A

Spectral: The Carotid

• Leg Arterial

• Mesenteric

• Uterine

• Penile

Spectral: Normal Physiology

Cavernosal A: Pre Post Injection

• Leg Arterial

• Umbilical A.

• Third trimester

Spectral: Pathology

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• Laminar Flow

Blood Flow Profile

• Plug Flow

Blood Flow Profile

• Laminar

• Helical

• Essential concept: Explains Inaccuracies

• Presume direction of flow

• Recommend 50-60 deg

Haemodynamic: “Normal flow”

The Importance of Doppler Angle of Insonation on Differentiation between 50–69% and 70–99% Carotid Artery Stenosis

Logason etal Eur J of Endo Surg. 2001

• 53 stenoses (51 patients) re-evaluated

• >50% stenosis

• Angle: Initial scan

• Mean 46°- PSV I81cm/s

• Angle: Re-scanned

• 60° - PSV 261cm/s

The Literature: Carotid Stenosis

• Spectral Broadening

• Mild

• Moderate

• Severe (Flow reversal)

• Audible

Blood Flow Profile

• PSV

• EDV

• Resistance

• Mono, Bi, Triphasic

• Blood Flow Profile

• Plug, Laminer, Spectral Broadening

• Conclusion

Some Examples…

“Signature Waveform”

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CCA Superficial Femoral A

Some Examples... Ulnar Artery

SFA Aorta- Which is which?

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How can we tell which direction? SMA

36yo male, cadaver, day 1

Poor urine output

Mild acute antibody rejection

DTPA Mag 3, Day 5 Bx

CCA (see next page as well)

CCA (more info) CCA

No CTA – Large infacrt

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ICA Vertebral

Carotid Bulb ICA

Hepatic A Appendix

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EIA

Groin

• Draw

• Pre- stenosis

• Stenosis

• Immediately post severe stenosis

• Very distal post severe stenosis

Anything else?