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.
4 Christian Doppler Australian mathematician and physicist Published his notable work on the Doppler effect at the age of 39Was Gregory Mendel’s physics professor in the University of Vienna.
5 Doppler EffectThe 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 Mathematical relationship Fd: Doppler shift= F[r] (received frequency)- F[t] (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)
8 Why do we care about the velocity of blood flow? Modified Bernoulli’s equation:DP= 4v2Gives us the ability to estimate pressure differences betweentwo chambers (i.e, TR)Stenotic valves (i.e. AS)
9 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°
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 analysisThe 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 axisVelocity- y axisToward 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 listeningReceives 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).
13 Clinical example- AS The position of the doppler beam is 2-D guided. In the GE system, it’s indicated by a single lineProfile 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?
16 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
17 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
18 Aliasing Sampling rate is inadequate to resolve the direction of flow PRF (pulse repetition frequency)- number of pulse transmitted from the transducer/secondNyquist limit= PRF/2Cannot 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 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: ambiguityAdvantage: Higher velocities can be analyzed without aliasing
22 Color Dopplerpulse wave Doppler with multiple sample volume along multiple raster linesdirection, velocity and variance determined for each sample volume
23 Color Doppler Displayed as color information- Amplitude- intensityDirection- 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)Different vendors have different algorithms for generating color Doppler
24 Example of Color Doppler Color Doppler jet encoded with varianceColor 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 regurgitationColor 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 ROALarger ROA may lead to lower velocityJet 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 lineDoppler velocity shift recorded and color codedProvides high temporal and spatial (but still not velocity) resolution to the assessment of flow
31 Color Doppler M-modeSmall amount of left to right flow during systole
32 Tissue Doppler Imaging Routine Doppler targets blood flowHigh velocityLow signal amplitudeTissue Doppler (assessing the movement of the myocardium) targets tissueLow velocityHigh signal amplitudeDifferent Filters
33 Example of pulse TDIVelocity of tissue along a particular sample volume
34 Example of Color TDIVelocity of tissue coded by color superimposed on 2-D imageCan derive information such as strain, strain rate, dyssynchrony…etc.