Doppler Echocardiography

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Doppler Echocardiography
Alex Tan M.D. 7/15/2009

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.

Outline Doppler Effect Continuous wave Doppler Pulse wave Doppler
Color Doppler Tissue Doppler New research applying principles of doppler echo

Christian Doppler Austrian mathematician and physicist
Published his notable work on the “Doppler Effect” at the age of 39 To explain the color of binary stars. Was Gregory Mendel’s physics professor in the University of Vienna.

Doppler Effect “Observed frequency of a wave depends on the relative speed of the source and observer” 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.

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

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

Doppler Shift and Velocity
Fd: Doppler shift= Fr (received frequency)- F0 (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) C= speed of sound in blood

Importance of blood flow velocity
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)

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°

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. Fd

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. Fd

Spectral analysis The difference in waveform between the transmitted and backscattered signal is compared. Data processed by Fourier transform (FFT) to display a spectral range of velocities Time- x axis Velocity- y axis Direction - toward the transducer is positive, away from transducer negative. Amplitude - “brightness” of the signal.

Continuous wave doppler
Two dedicated crystals- one for transmitting and one for receiving. 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).

Clinical example- AS The position of the doppler beam is 2-D guided.
Profile is usually filled in- velocity along the path that is below the maximal velocity also represented.

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

Problematic cases AS or MR?

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

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

Aliasing Sampling rate is inadequate to resolve the direction of flow
Nyquist limit= PRF/2 PRF (pulse repetition frequency) - number of pulse transmitted from the transducer/second

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)

Aliasing Tends to happen at higher velocity jets
Methods to overcome aliasing include baseline shift, continuous doppler, high PRF imaging.

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: range ambiguity Advantage: Higher velocities can be analyzed without aliasing

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

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)

Example of Color Doppler

Color Gain

Semiquantitative method
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.

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

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

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.

Applications of tissue doppler
1036 patients from community based population study Do patients with normal LV by conventional echo but abnormal systolic and diastolic function by TDI have increased mortality?

Background TDI assessing LV systolic and diastolic function has been shown to have prognostic significance. However, data conflicting. Has not been applied to a large community population.

Methods Conventional echo (2D, MM, PD mitral) Color TDI:
To rule out patients with LVEF<50%, severe diastolic dysfunction, LVH, LV dilatation Color TDI: 6 mitral annular positions Peak systolic (s’), early diastolic (d’), late diastolic (a’)

Color TDI parameters E/e’ e’/a’ e’/(a’x s’)

Patient characteristics
1100 patients studied 19 excluded for AF or significant valvulopathy 45 excluded for poor quality images.

Results Model 1: adjusted for age and sex
Model 2: adjusted for LVH, LV dilatation, LVEF<50% Model 3: included only those with normal conventional echo

Prognostic significance of Eas index
Kaplan Meier Survival curves of age and sex adjusted tertiles of Eas [e’/(a’ x s’)]

Incremental value of TDI in predicting mortality