2 Doppler vs. B-mode Echo- complementary roles Primary target is the red blood cellExamine the direction, velocity, and pattern of blood flow through the heart and the great vessels.Primary target are the myocardium and the heart valvesProvides information about the shape and movement of cardiac structures.
3 Outline Doppler Effect Continuous wave Doppler Pulse wave Doppler Color DopplerTissue DopplerNew research applying principles of doppler echo
4 Christian Doppler Austrian mathematician and physicist Published his notable work on the “Doppler Effect” at the age of 39To explain the color of binary stars.Was Gregory Mendel’s physics professor in the University of Vienna.
5 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 listenerSound 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 increasesIf RBC (flow of blood) moves away from the transducer, frequency of the reflected sound’s wavelength decreases
7 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 increasesIf RBC (flow of blood) moves away from the transducer, frequency of the reflected sound’s wavelength decreases
8 Doppler Shift and Velocity Fd: Doppler shift= Fr (received frequency)- F0 (transmitted frequency)F0: Transmitted frequency of ultrasoundV: velocity of blood.q: intercept angle between the interrogation beam and the targetCan solve for V=Fd(C)/2f0(cos q)C= speed of sound in blood
9 Importance of blood flow velocity Modified Bernoulli’s equation:DP= 4v2Gives us the ability to estimate pressure differences betweentwo chambers (i.e, TR)Stenotic valves (i.e. AS)
10 Angle of the Doppler beam cos (0°)= 1cos (10°)= 0.98cos (20°)= 0.94cos (30°)= 0.87cos (60°)= 0.5cos (90°)= 0Fd= 2f0(V)(cos q)/CFd d V(cos q)Misalignment of the interrogation beam will lead to underestimation of the true velocityBecomes significant when q is >20°
11 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
12 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
13 Spectral analysisThe difference in waveform between the transmitted and backscattered signal is compared.Data processed by Fourier transform (FFT) to display a spectral range of velocitiesTime- x axisVelocity- y axisDirection - toward the transducer is positive, away from transducer negative.Amplitude - “brightness” of the signal.
14 Continuous wave doppler Two dedicated crystals- one for transmitting and one for receiving.Receives a continuous signal along the entire length of the ultrasound beamDisadvantage- 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).
15 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.
16 Problematic cases Don’t know where the maximal velocity comes from Serial stenosis- LVOT obstruction or AS?
18 Pulse wave dopplerShort intermittent busts of ultrasound are transmitted.Only “listens” at a brief time intervalPermits returning signal from one specific distance to be selectively analyzed- “range resolution”Sample volume
19 Clinical Examples position of doppler beam 2-D guided In GE system, the sample volume is indicated by double linesSpectral envelope not filled inCommon use- mitral inflow velocity and LVOT velocity
20 Aliasing Sampling rate is inadequate to resolve the direction of flow Nyquist limit= PRF/2PRF (pulse repetition frequency) - number of pulse transmitted from the transducer/second
21 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)
22 Aliasing Tends to happen at higher velocity jets Methods to overcome aliasing include baseline shift, continuous doppler, high PRF imaging.
23 High PRF imagingShallower sample volume associated with a higher PRF- less likely to have aliasingListening window will also sample returning signal from twice that depthVelocity from both sites will be recordedDisadvantage: range ambiguityAdvantage: Higher velocities can be analyzed without aliasing
24 Color Dopplerpulse wave Doppler with multiple sample volume along multiple scan linesdirection, velocity and variance determined for each sample volume
25 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 imagesTime consuming (temporal resolution is especially poor with a large sector window)
28 Semiquantitative method Color codes velocity and not actual volume!Angiography- contrast is actual regurgitationColor doppler encodes “billard ball effect”- color may encode non-regurgitant blood that is “pushed around” by the regurgitant jet.
29 Tissue Doppler Imaging Routine Doppler targets blood flowHigh velocityLow signal amplitudeTissue Doppler (assessing the movement of the myocardium) targets tissueLow velocityHigh signal amplitudeDifferent Filters
30 Example of pulse TDIVelocity of tissue along a particular sample volume
31 Example of Color TDIVelocity of tissue coded by color superimposed on 2-D imageCan derive information such as strain, strain rate, dyssynchrony…etc.
32 Applications of tissue doppler 1036 patients from community based population studyDo patients with normal LV by conventional echo but abnormal systolic and diastolic function by TDI have increased mortality?
33 BackgroundTDI 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.
34 Methods Conventional echo (2D, MM, PD mitral) Color TDI: To rule out patients with LVEF<50%, severe diastolic dysfunction, LVH, LV dilatationColor TDI:6 mitral annular positionsPeak systolic (s’), early diastolic (d’), late diastolic (a’)