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 shiK (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. Insona+on Angle 1 0.9 0.8 0.7 0.6 0.5 Cosine 0.4 0.3 0.2 0.1 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Insona+on Angle FD = 2F0 v cos θ / c Percent Change vs. Insona+on Angle 100 90 80 70 60 50 40 Percent Change 30 20 10 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Insona+on 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 – Poten<al (gravity) – Iner<al (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 Iner<al 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 Cri<cal Stenosis Stenosis narrows, velocity As velocity , Reynolds numBer Laminar flow lost to turBulence Energy losses Perfusion is impaired Elevated veloci<es infer energy loss Downstream perfusion impaired “Significant” or “Cri<cal” stenosis Adapted From: Taylor, Burns, and Wells. Clinical Applications of Doppler Ultrasound PSV AT Waveform V Velocity vs. Time Local condi<ons EDV Proximal / upstream condi<ons T Stenoses, cardiac output, shunts Distal / downstream condi<ons Impedance (pressure, vessel diameter, etc) Peak Systolic Velocity Increased Larger volume flow Stenosis (length, impedance) SMA fas<ng Decreased Low volume flow Cri<cal stenosis SMA post-prandial Liver - Portal Vein Fas<ng Post-prandial End Diastolic Velocity Increased Low impedance (vasodilataon) Downstream from stenosis Decreased High impedance (vasoconstric<on) 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) Sensi<ve 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] facebook.com/CincyKidsRad @CincyKidsRad @bdcoleymd .