What’s going on in here? •Doppler Effect •Color Displays...
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1 What’s going on in here? • Doppler Effect • Color Displays • Spectral Displays • Aliasing Christian Andreas Doppler 1803 - 1853 Courtesy Alec Eden The Christian Doppler Foundation Why is he not smiling? Salzburg, Austria Salzach River 1756 - 1791 You just heard _______________ a train whistle? Amtrak?
Transcript of What’s going on in here? •Doppler Effect •Color Displays...
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What’s goingon in here? • Doppler Effect
• Color Displays• Spectral Displays• Aliasing
Christian Andreas Doppler1803 - 1853
Courtesy Alec EdenThe Christian Doppler Foundation
Why is henot smiling? Salzburg, Austria
Salzach River
1756 - 1791You just heard _______________a train whistle?Amtrak?
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Kremkau
fD = fR - fT =2 fT v
c
transducer vfR
fTfD =
2 fT v cos θc
θ
Presence of flow
Direction of flow
Speed of flow
Character of flow
Yes or No ?
Which Way ?
How Fast ?
What kind ?
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Audible Sounds
Color-Doppler Display
Spectral Display
DISPLAY
Doppler-shift Detector
SIGNALPROCESSOR
IMAGEPROCESSOR
BEAMFORMER
amplitude
T
dop
Color Doppler
Baseline and wall filter
Increasing positivedopplershift
Increasing negativedopplershift
flow
transducer
upstream view (positive shift)
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flow
transducer
downstream (negative shift)
head
power
NASADemo2.20
5
World Book, Inc.
color (frequency) spectrum
ampl
itude
→
freq
uenc
y →
time →
frequency →
Time
Dopplershift orvelocity
FFT'sDoppler-shift Detector Spectrum Analyzer
SIGNALPROCESSOR
IMAGEPROCESSOR
BEAMFORMER
amp
TGated Amplifier
dop
Pulsed Spectral Doppler
13
26
39
52
65
78
91
104
C.R.B. Merritt, MD
6
DuplexPulsedDoppler
Gray-scaleImaging+ =
flow
transducer
upstream view (positive shift)
flow
transducer
downstream (negative shift)
stenosis plaque
turbulence
fast
proximal
7
at stenosisdistal
Demo5.00
Popliteal Artery
Normal Kidney
Tardus-parvus waveformPellerito & Zwiebel 2005
ARTIFACT-FREE
Fan1.30
StrobeMagic
0
0
0
000
00
0
0
1 kHz
PRF = 10 kHz[sampling rate]
0
0
0
0
00
0
0
00
3 kHz
8
00
00
0
0
0 0
0
0
6 kHz
PRF = 10 kHz
0
0
0
000
00
0
0
9 kHz
PRF = 10 kHz
NYQUIST LIMIT
2 samples per cycle
i.e., prf > 2 x doppler-shift frequency
Kentucky DerbyWinner 2016Nyquist on
Nyquist0
0
0
000
00
0
0 1 kHz
PRF = 10 kHzNyquist Limit = 5 kHz
9 kHz
0
0
0
000
00
0
0
LIMIT
NYQUIST
1/2 PRF
1.25
1.75
1.75
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CUTPASTE
1.75
1.25
i.e. cut and pasteshift baseline down
increase prf (scale)[3.50 before]
Correcting for Aliasing
• shift baseline up/down (first)
• increase prf (scale)
NC-ACRPart B
Panda Clev ClinPart 2
Demo4.00
Color-DopplerAliasing
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IncreasingpositiveDopplershift(correct)
IncreasingpositiveDoppler shift(aliased todecreasingnegative shift)
ALIASING
REVERSAL
Greg MarieJohnGeneREV SteveMarsha
ReviewTest
QAS30
