Transcript Doppler Echocardiography

Doppler Echocardiography
Joyce Meng M.D.
7/16/2008
Doppler vs. B-mode Echocomplementary roles
 Primary target is the
 Primary target are the
red blood cell
myocardium and the
heart valves
 Examine the
direction, velocity, and  Provides information
pattern of blood flow
about the shape and
through the heart and
movement of cardiac
the great vessels.
structures.
Outline
Doppler Effect
Continuous wave Doppler
Pulse wave Doppler
Color Doppler
Tissue Doppler
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.
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.
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
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)
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)
Angle of the Doppler beam
 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°
 cos
 cos
 cos
 cos
 cos
 cos
(0°)= 1
(10°)= 0.98
(20°)= 0.94
(30°)= 0.87
(60°)= 0.5
(90°)= 0
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.
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.
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).
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.
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
 PRF (pulse repetition frequency)- number of pulse
transmitted from the transducer/second
 Nyquist limit= PRF/2
 Cannot resolve higher frequency (velocity) sound waves
Aliasing
 Tends to happen at higher velocity jets
 Doppler shift is has higher frequency- needs
higher PRF to resolve the direction of the wave.
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)
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
Color Doppler
 pulse wave Doppler with multiple sample volume
along multiple raster 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)
 Different vendors have different algorithms for
generating color Doppler
Example of Color Doppler
Color Doppler jet
encoded with
variance
Color Doppler jet
with aliasing in
the center due to
high velocity
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 nonregurgitant blood that is
“pushed around” by the
regurgitant jet.
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.
Color gain
Same jet with different
color gain appears
different.
Color gain is turns up
or down the
amplitude of the color
jet.
Color gain
then turn it down
slightly
To optimize color gain,
turn it up until you see
speckles in the tissues-
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
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
Color Doppler M-mode
Small amount of left to right flow during
systole
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.