Doppler Imaging: The Basics

Transcription

1 Doppler Imaging: The Basics Brian D. Coley, MD, FACR Cincinna< Children s Hospital Medical Center Cincinna<, Ohio

2 Doppler Equa<on F D = 2F V 0 cos θ / c F D = Doppler shik (measured) F 0 = insona<ng frequency (known) θ = angle of insona<on (measured) c = speed of sound (1540 m/sec)

3 F D = 2F 0 v cos θ / c Cosine vs. Insona+on Angle Cosine Insona+on Angle

4 F D = 2F 0 v cos θ / c Percent Change vs. Insona+on Angle Percent Change Insona+on Angle

5 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

6 Parabolic Laminar Flow

7 Parabolic Laminar Flow Narrow gate Wide gate

8 Bernoulli s Principle Flow is constant Q = Velocity x Area Daniel Bernoulli Q 1 = Q 2 = Q 3

9 Poiseuille s Law Q = ΔP (π r 4 /8lη) Flow Pressure ΔP = pressure change r = vessel radius l = vessel length η = fluid viscosity Assumes steady flow, rigid tube Jean Louis Marie Poiseuille

10 Hemodynamics - in vivo Blood flow - difference in fluid energy Pressure Kine<c Poten<al (gravity) Iner<al (pulsa<le systems) Viscous (usually neg) Energy is conserved Isaac Newton

11 Theory Flow constant To maintain flow: velocity, pressure Laminar flow maintained Adapted From: Taylor, Burns, and Wells. Clinical Applications of Doppler Ultrasound

12 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

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

14 Reynolds Number R Laminar Flow Turbulent Flow Osborne Reynolds R velocity R=dvρ/η Adapted From: Taylor, Burns, and Wells. Clinical Applications of Doppler Ultrasound sageography.myschoolstuff.co.za d = vessel diameter v = velocity ρ = fluid mass density η = fluid viscosity For blood R = 2300

15 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

16 Waveform Velocity vs. Time V PSV AT Local condi<ons EDV Proximal / upstream condi<ons T Stenoses, cardiac output, shunts Distal / downstream condi<ons Impedance (pressure, vessel diameter, etc)

17 Peak Systolic Velocity Increased Larger volume flow Stenosis (length, impedance) SMA fas<ng Decreased Low volume flow Cri<cal stenosis SMA post-prandial

18 Liver - Portal Vein Fas<ng Post-prandial

19 End Diastolic Velocity Increased Low impedance (vasodilata<on) Downstream from stenosis Decreased High impedance (vasoconstric<on) SFA pre exercise SFA post exercise

20 Accelera<on Time Normally very short (< 0.07 s) Delayed Stenosis High compliance Low resistance (AVF) High downstream area

21 Hemodynamics - Veins Isolated from arterial pulsa<on Slower flow Turbulence uncommon (R velocity) Sensi<ve to downstream pressures

22 Always Remember Medica<ons Shunts Cardiac disease

23 Hepa<c Artery - Pressors Epi No Epi

24 Cardiac Disease Aor<c Coarcta<on PDA

25 Abnormal hepa<c waveforms

26 Tricuspid atresia with intact septum and elevated right heart pressures

27 The Quick Review Poiseuille Flow Pressure Bernoullie Jean Louis Marie Poiseuille Constant volume flow through stenosis Reynolds Turbulence velocity Daniel Bernoulli Osborne Reynolds

28 The Quick Review PSV volume flow and stenoses EDV impedance AT stenoses and impedance

29 Conclusions Proper<es of blood flow Conserva<on of flow and energy Laminar vs. turbulent flow Behavior with stenoses, impedance Doppler waveform - velocity vs. <me PSV, EDV, AT

30 Conclusions Doppler is good And it s not that hard Predictable blood flow altera<ons allow applica<on to clinical scenarios Makes US more fun and rewarding

31 @bdcoleymd