Doppler Imaging: The Basics

Brian D. Coley, MD, FACR Cincinna Children’s Hospital Medical Center Cincinna, Ohio [email protected]

facebook.com/CincyKidsRad @CincyKidsRad @bdcoleymd Doppler Equaon

• FD = 2F0 V cos θ / c

• FD = Doppler shi (measured)

• F0 = insonang frequency (known) • θ = angle of insonaon (measured) • c = speed of sound (1540 m/sec) FD = 2F0 v cos θ / c

Cosine vs. Insonaon Angle 1

0.9

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0.5 Cosine 0.4

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0.1

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Insonaon Angle FD = 2F0 v cos θ / c Percent Change vs. Insonaon Angle 100

90

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40 Percent Change 30

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0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Insonaon Angle Hemodynamics

• Flow in most vessels laminar • Blood viscous - shear stress • Parabolic velocity profile – Near zero at edge (boundary layer) – Mean velocity ≈ 1/2 max velocity Parabolic Laminar Flow Parabolic Laminar Flow

Narrow gate Wide gate Bernoulli’s Principle

• Flow is constant • Q = Velocity x Area

Daniel Bernoulli 1700 - 1782 1 2 3

Q1 = Q2 = Q3 Poiseuille’s Law

Q = ΔP (π r4/8lη) Flow ≈ Pressure ΔP = pressure change r = vessel radius l = vessel length Jean Louis Marie Poiseuille η = fluid viscosity 1799 - 1869 Assumes steady flow, rigid tube

Hemodynamics - in vivo • Blood flow - difference in fluid energy – Pressure – Kinec – Potenal (gravity) – Ineral (pulsale systems) – Viscous (usually neg) • Energy is conserved

Isaac Newton 1643 - 1727 Theory

Flow constant To maintain flow: velocity, pressure Laminar flow maintained

Adapted From: Taylor, Burns, and Wells. Clinical Applications of Doppler Ultrasound Reality

Energy lost through stenosis Shape, length, η Ineral losses Viscous losses

Downstream pressure may be maintained

Adapted From: Taylor, Burns, and Wells. Clinical Applications of Doppler Ultrasound Reynolds Number R

Turbulent Laminar Osborne Reynolds Flow Flow 1842 - 1912 R ≈ velocity

R = d v ρ / η d = vessel diameter v = velocity ρ = fluid mass density = fluid viscosity Adapted From: Taylor, Burns, and Wells. η Clinical Applications of Doppler Ultrasound For blood R = 2300 Reynolds Number

R

Turbulent • Laminar Osborne Reynolds • Flow Flow 1842 - 1912 R ≈ velocity

R = d v ρ / η d = vessel diameter v = velocity ρ = fluid mass density = fluid viscosity Adapted From: Taylor, Burns, and Wells. η Clinical Applications of Doppler Ultrasound sageography.myschoolstuff.co.za For blood R = 2300 Crical Stenosis

Stenosis narrows, velocity As velocity , Reynolds number Laminar flow lost to turbulence Energy losses Perfusion is impaired

Elevated velocies infer energy loss Downstream perfusion impaired “Significant” or “Crical” stenosis

Adapted From: Taylor, Burns, and Wells. Clinical Applications of Doppler Ultrasound PSV AT Waveform V Velocity vs. Time Local condions EDV Proximal / upstream condions T Stenoses, cardiac output, shunts Distal / downstream condions Impedance (pressure, vessel diameter, etc) Peak Systolic Velocity

Increased Larger volume flow Stenosis (length, impedance) SMA fasng Decreased Low volume flow Crical stenosis

SMA post-prandial Liver - Portal Vein

Fasng Post-prandial End Diastolic Velocity Increased Low impedance (vasodilataon) Downstream from stenosis Decreased High impedance (vasoconstricon)

SFA pre SFA post exercise exercise Acceleraon Time

Normally very short (< 0.07 s)

Delayed Stenosis High compliance Low resistance (AVF) High downstream area Hemodynamics - Veins

Isolated from arterial pulsaon Slower flow Turbulence uncommon (R ≈ velocity) Sensive to downstream pressures Always Remember

Medicaons Shunts Cardiac disease Hepac Artery - Pressors

Epi

No Epi Cardiac Disease

Aorc Coarctaon

PDA Abnormal hepac waveforms… Tricuspid atresia with intact septum and elevated right heart pressures The Quick Review Poiseuille Flow ≈ Pressure

Jean Louis Marie Poiseuille Bernoullie 1799 - 1869 Constant volume flow through stenosis

Daniel Bernoulli Reynolds 1700 - 1782 Turbulence ≈ velocity

Osborne Reynolds 1842 - 1912 The Quick Review

PSV – volume flow and stenoses

EDV – impedance

AT – stenoses and impedance Conclusions

Properes of blood flow Conservaon of flow and energy Laminar vs. turbulent flow Behavior with stenoses, impedance Doppler waveform - velocity vs. me PSV, EDV, AT Conclusions

Doppler is good And it’s not that hard Predictable blood flow alteraons allow applicaon to clinical scenarios Makes US more fun and rewarding [email protected]

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