1. Doppler Echocardiography
Joyce Meng M.D.
7/16/2008

2. Doppler vs. B-mode Echo- complementary roles
Primary target is the red blood cell
Examine the direction, velocity, and pattern of blood flow through the heart and the great vessels.
Primary target are the myocardium and the heart valves
Provides information about the shape and movement of cardiac structures.

3. Outline Doppler Effect Continuous wave Doppler Pulse wave Doppler
Color Doppler
Tissue Doppler

4. Christian Doppler Australian mathematician and physicist
Published his notable work on the Doppler effect at the age of 39
Was Gregory Mendel’s physics professor in the University of Vienna.

5. Doppler Effect
The pitch of sound was affected by motion toward or away from the listener
Sound moves toward the listener, frequency increases, pitch rises.
Sound moves away from the listener, frequency decreases, pitch falls.

6. Doppler effect applied to Echocardiography
Transducer emits ultrasound reflected from RBC.
If RBC (flow of blood) moves toward transducer, frequency of the reflected sound’s wavelength increases
If RBC (flow of blood) moves away from the transducer, frequency of the reflected sound’s wavelength decreases

7. Mathematical relationship
Fd: Doppler shift= F[r] (received frequency)- F[t] (transmitted frequency)
F0: Transmitted frequency of ultrasound
V: velocity of blood.
q: intercept angle between the interrogation beam and the target
Can solve for V=Fd(C)/2f0(cos q)

8. Why do we care about the velocity of blood flow?
Modified Bernoulli’s equation:
DP= 4v2
Gives us the ability to estimate pressure differences between
two chambers (i.e, TR)
Stenotic valves (i.e. AS)

9. Angle of the Doppler beam
cos (0°)= 1
cos (10°)= 0.98
cos (20°)= 0.94
cos (30°)= 0.87
cos (60°)= 0.5
cos (90°)= 0
Fd= 2f0(V)(cos q)/C
Fd d V(cos q)
Misalignment of the interrogation beam will lead to underestimation of the true velocity
Becomes significant when q is >20°

10. Carrier frequency V=Fd(C)/2f0(cos q)
If Fd stays the same, the lower the f0 (carrier frequency), the higher the velocity of the jet that can be resolved.
Unlike B-mode imaging where higher frequency transducer gives better resolution, here lower frequency transducers gives better resolution.

11. Spectral analysis
The difference in waveform between the transmitted and backscattered signal is compared.
A process called fast Fourier transform (FFT) displays this information into a “spectral analysis” (spectral display of entire range of velocities)
Time- x axis
Velocity- y axis
Toward the transducer is positive, away from transducer negative.
Amplitude is displayed as “brightness” of the signal.

12. Continuous wave doppler
Two dedicated crystals- one for transmitting and one for listening
Receives a continuous signal along the entire length of the ultrasound beam
Disadvantage- don’t know where the signal comes from.
Advantage- can measure very high Doppler shift/velocities.
Most useful when trying to discern maximal velocity along a certain path (AS, TR…etc).

13. Clinical example- AS The position of the doppler beam is 2-D guided.
In the GE system, it’s indicated by a single line
Profile is usually filled in- velocity along the path that is below the maximal velocity also represented.

14. Problematic cases Don’t know where the maximal velocity comes from
Serial stenosis- LVOT obstruction or AS?

15. Problematic cases
AS or MR?

16. Pulse wave doppler
Short intermittent busts of ultrasound are transmitted.
Only “listens” at a brief time interval
Permits returning signal from one specific distance to be selectively analyzed- “range resolution”
Sample volume

17. Clinical Examples position of doppler beam 2-D guided
In GE system, the sample volume is indicated by double lines
Spectral envelope not filled in
Common use- mitral inflow velocity and LVOT velocity

18. Aliasing Sampling rate is inadequate to resolve the direction of flow
PRF (pulse repetition frequency)- number of pulse transmitted from the transducer/second
Nyquist limit= PRF/2
Cannot resolve higher frequency (velocity) sound waves

19. Aliasing Tends to happen at higher velocity jets
Doppler shift is has higher frequency- needs higher PRF to resolve the direction of the wave.

20. Aliasing Tends to happen in at greater depth
Sample volume at a shallow site- can interrogate more frequently (higher PRF)
Sample volume at deeper site- cannot interrogate as often (lower PRF)

21. High PRF imaging
Shallower sample volume associated with a higher PRF- less likely to have aliasing
Listening window will also sample returning signal from twice that depth
Velocity from both sites will be recorded
Disadvantage: ambiguity
Advantage: Higher velocities can be analyzed without aliasing

22. Color Doppler
pulse wave Doppler with multiple sample volume along multiple raster lines
direction, velocity and variance determined for each sample volume

23. Color Doppler Displayed as color information-
Amplitude- intensity
Direction- red vs blue (toward or away from transducer)
Velocity- brightness (bright blue higher velocity)
Variance (turbulence)- coded green to give a mosiac apperance.
Overlays this information on 2D images
Time consuming (temporal resolution is especially poor with a large sector window)
Different vendors have different algorithms for generating color Doppler

24. Example of Color Doppler
Color Doppler jet encoded with variance
Color Doppler jet with aliasing in the center due to high velocity

25. Semiquantitative method
Important to remember that color codes velocity and not actual volume!
Angiography- contrast is actual regurgitation
Color doppler encodes “billard ball effect”- color may encode non-regurgitant blood that is “pushed around” by the regurgitant jet.

26. Semiquantitative method
Measures velocity, not regurgitant orifice area (ROA)
Velocity can be inversely proportional to ROA
Larger ROA may lead to lower velocity
Jet looks smaller than a those with smaller ROA.

27. Color gain Same jet with different color gain appears different.
Color gain is turns up or down the amplitude of the color jet.

28. Color gain then turn it down slightly
To optimize color gain, turn it up until you see speckles in the tissues-

29. Color scale/ Nyquist limit
Should set the Nyquist limit to the highest a given depth allows (generally >0.6 cm/s)
By changing the color Nyquist limit, the jet appearance and size can appear different

30. Color Doppler M-mode imaging
Pulse Doppler interrogation done along a single line
Doppler velocity shift recorded and color coded
Provides high temporal and spatial (but still not velocity) resolution to the assessment of flow

31. Color Doppler M-mode
Small amount of left to right flow during systole

32. Tissue Doppler Imaging
Routine Doppler targets blood flow
High velocity
Low signal amplitude
Tissue Doppler (assessing the movement of the myocardium) targets tissue
Low velocity
High signal amplitude
Different Filters

33. Example of pulse TDI
Velocity of tissue along a particular sample volume

34. Example of Color TDI
Velocity of tissue coded by color superimposed on 2-D image
Can derive information such as strain, strain rate, dyssynchrony…etc.