1. DOPPLER PHYSICS
By Dr Nani Lampung
Junior Resident
Dept of Radiodiagnosis
JNMCH AMU ALIGARH
2. PRINCIPLE OF DOPPLER
ULTRASOUND
• BASIS – ‘ DOPPLER EFFECT’
• DISCOVERY – Physicist Christian Johann
Doppler in 1842
• ‘When a sound source and the reflector
are moving toward each other, the sound
waves are spaced closer together and reach
the reciever at a higher frequency than
they were originally emitted ’.
3.
4.
5. • Doppler shift isthedifference
between thetransmitted and
received frequencies
• Transmitted and received
Frequenciesarein theMHz range
Doppler shift frequenciesoften in
audiblerange
DOPPLER SHIFT
7. • Relationship between Doppler shift (or just Doppler)
frequency, FD and reflector velocity, v:
fo istheultrasound frequency, or thetransmitted beam
frequency.
v isthereflector velocity (m/s; cm/s)
q istheDoppler angle
c isthespeed of sound
DOP
P
LEREQUATION
c
cosθ
v
2f
F o
D =
12. • Usesbrief pulsesof ultrasound energy using only one
crystal.
• Theecho delay time( Te) can beconverted into distance
and theDEPTH of echo sourcecan bedetermined
• Thesensitivevolumefrom which flow dataaresampled
can becontrolled in termsof shape, depth, and position.
PULSED-WAVE (PW) DOPPLER
13. DUP
L
E
X UL
T
RASOUND
SCANNING
Duplex ultrasound instrumentsarereal-timeB-modescanners
with built-in Doppler capabilities.
● B
-mode Imager( Outlineanatomic structures)
● P
ulsed-Doppler ( Flow and movement patterns)
14. PULSED WAVE DOPPLER
P
UL
SERE
P
E
T
IT
ION F
RE
QUE
NCY ( P
R
F)-
No. of pulses transmitted per second
• With increasing scanning depth PRF decreasesasmoretimeis
needed for theechoesto return
• At aminimum, thePRF must beat least twice the
frequency of theDoppler signal to construct thesignal
successfully.
• Thissetsupper limit to theflow velocitiesto beaccurately
recorded
• Usehigher PRF setting for high flow velocities, low PRF for
slow venousflow
17. SPECTRAL DOPPLER
• Ultrasound isemitted in pulsessimilar to B-mode
• Gate is used to determine the interval after emission
when returning signalsarereceived and thereforethedepth
from which thesampleistaken.
• The Doppler shift data are displayed in graphic form as a
time-varying plot of the frequency spectrum of the
returning signal.
• A fast F
ourier transformation is used to perform the
frequency analysis.
18. • SPECTRAL ANALYSIS shows the Doppler shift
spectrum and direction ,usually displayed as the
maximum velocity rather than frequency
• ProvidesQUANTITATIVE INFORMATION
19. Theresulting Doppler frequency spectrum
displaysthefollowing :
Variation with time of the Doppler frequencies
present in thevolumesampled.
The envelope of the spectrum, representing the
maximum frequencies present at any given point in
time.
Thewidth of the spectrum at any point, indicating
therangeof frequenciespresent.
25. DOPPLER SPECTRUM
ASSESSMENT
DIRECTION OF FLOW
• Pulsed doppler usequadraturephasedetection
to providebidirectional doppler information
F
L
OWCAN E
IT
H
E
RB
E
• Mono-phasic
• Bi-phasic
• Tri-phasic
• Bidirectional
30. AM
P
L
IT
UDE
• Thespectrum displaysecho amplitude by varying the
brightnessof thedisplay
Theamplitudeof theechoesaredetermined by
• Echo intensity
• Power
• Gain
• Dynamic range
DOPPLER SPECTRUM
ASSESSMENT
34. SPECTRUM BROADENING
- Loss of spectral window is called SPECTRAL
BROADENING
OCCURS-
• As the blood decelerates in diastole
• SV placed close to the vessel wall
• In small vessels ( parabolic velocity profile )
37. P
UL
SAT
IL
IT
Y
• Measuresthedifferencebetween themaximum and minimum
velocitieswithin thecardiac cycle
• Indicesareunit less
• All increasein valueasflow pulsatility increases
• Can bemeasured without knowledgeof thedoppler angle
DOPPLER SPECTRUM
ASSESSMENT
38.
39. DOP
P
L
E
RINDICE
S
• PI = S-D/Vm ( GOSLING )
• RI = S-D/S( POURCELOT )
• S/D Ratio
• Acceleration time( AT) & Acceleration Index ( AI)
• SPECTRAL BROADENING
40. COLOUR DOPPLER
• Based on pulsed doppler technique.
• Doppler shifts- converted to colour and the
moving blood isdisplayed in colorsthat
correspond to itsvelocity and direction.
41. COLOUR DOPPLER
• PositiveDoppler shiftsareencoded asred and negative
shiftsareencoded asblue.
• Velocity of theflow isrepresented in shadesof color -
faster - brighter
43. COLOR BOX
• Operator adjustableareawithin the
USimage
• AffectsImageresolution & quality
( changein box size)- Framerate
decreaseswith increasing box size
• Assmall & superficial aspossible
• Deep color box – slower PRF
resultsaliasing
COL
ORDOP
P
L
E
R.
46. COLOUR DOPPLER
Advantages
It providesan overall view of flow in organ or structure
Providesdirectional information about flow,
Providesvelocity information about flow and shows
turbulent typeflow
L
imitations
• SEMI QUANTITATIVE
• Angledependence
• Aliasing
• Artifactscaused by the noise
• Poor temporal resolution
48. SPECTRAL DOPPLER
• DEPICTION OF DOPPLER
SHIFT INFORMATION IN
WAVEFORM
COLOUR DOPPLER
• UTILIZE DOPPLER SHIFT
INFORMATION TO SHOW
BLOOD FLOW IN COLOR
50. POWER DOPPLER
• Also known asEnergy Doppler / AmplitudeDoppler.
• In thismode, colour isassigned to thepower /strength/ energy
of theDoppler signal rather than theDoppler frequency shift.
• Flow isusually displayed with onecolour
USE
S
• To detect very slow flow, flow in small vessels, or where
transducer angling isawkward.
• Power Doppler can beused in conjunction with contrast
agentsof varying brightness
56. OP
T
IM
ISAT
ION OFCOL
ORF
L
OW
DOP
P
L
E
RE
XAM
INAT
ION
4. W
all F
ilters.
• Cut off of thelow frequency noises, a
cleaner high velocity blood flow signal is
displayed.
• If set too high theblood flow is
discarded, if set low noisewill bemore.
5. DopplerGain.
• Controlstheamplitudeof thecolour
display in colour or power Doppler mode
& thespectral display in pulseDoppler
mode.
Excess gain Proper gain Insufficent gain
PSV = 75 cm/sec 60 cm/sec 50 cm/sec
57. OP
T
IM
ISAT
ION OFCOL
ORF
L
OW
DOP
P
L
E
RE
XAM
INAT
ION
6. Velocity scale.
• Controlstherangeof frequenciesdisplayed
• Too high scale- dynamic rangeistoo largeand low
velocity signalsaremissed simulating an areaof
thrombosis
• If scaleistoo low thedynamic rangeistoo small to
display thehigh velocity signalsaccurately resulting in
aliasing.
59. • AL
IASING
An inaccuratedisplay of
colour or spectral Doppler
velocity when thevelocity
rangeexceedsthescale
availableto display it.
Nyquist sampling rate-
PRF = 2 x fD
DOPPLER ARTIFACTS
60.
61. How to reduce ALIASING ?
• Drop thebaseline
• Increasetheavailablevelocity range.
• DecreasetheDoppler frequency shift
by using alower insolating frequency
or
• Increasing theDoppler angle.
62. • P
owerDopplerhas no aliasing becauseit hasno
directional or velocity component.
Advantage: -
• 1. useful for localizing thehighest velocity region.
• 2. It isused in identifying theabnormal areain T
IP
SS & in
localizing AV fistulae.
Disadvantage:- high velocity may not beaccurately measured.
64. DOPPLER ARTIFACTS
F
lash Artifact
• Manifestsasacolor signal dueto
transducer or patient motion
• It isseen in left lobeof liver dueto cardiac
pulsation and in hypoechoic areassuch as
cystsand fluid collections.
65. DOPPLER ARTIFACTS
M
irrorImage artifact :
• displays objects on both sides of a strong
reflector,
• The reflectors (diaphragm, pleural surface
and aortic wall) directs some of the
echoes to a second reflector before it
returns them to the transducer resulting
multipath reflection.
• Eg Duplication of sub clavian artery
(pleura reflector)
67. GUIDELINESFOR AN OPTIMAL
COLOUR FLOW DOPPLER
EXAMINATION.
• Thecolour flow box should bekept assmall & superficial as
possible
• Adjust thegain and filter settings
• Adjust thevelocity scale(PRF) and baselineaccording to the
flow conditions.
68. • Obtain an optimal Doppler angleby adjusting thebeam
steering and probeposition. ( 600
or less)
• Adjust thepulsed Doppler samplevolumesize(gate)
appropriately (2/3rd
of thevelocity diameter)
• AVOID TRANSDUCER MOTION.
69. RECENT INNOVATIONS
IN DOPPLER US TECHNIQUES
• Doppler USisexperiencing technical innovationsthat also
contributeto improved B-modeimaging.
1 Extended field of view imaging
2 (a) wideband, widedynamic rangesystems- improvethe
sensitivity of Doppler US;
(b) Viaincorporation of custom-designed integrated
circuitry.- Doppler USprocessing on even handheld US
scanners.
• 3 Contrast agentshavebecomemuch morethan simple“echo
enhancers” for Doppler instrumentation.
70. REFERENCES
1. Diagnostic Ultrasound, Carol M Rumack and others, 4th
ed.
2. Grainger & Allison’sDiagnostic Radiology- A Textbook of Medical
Imaging, 6th
ed.
3. Teaching Manual of Color Duplex Sonography,2nd
ed.
4. Frederick W. Kremkau, Diagnostic Ultrasound - Principlesand
Instruments, 7th Edition, St. Louis,-Missouri, SaundersElsevier, 2006
5. Rubin JM ,BudeRO CarsonPL et al ;Power Doppler US; A
potentiallyuseful alternativeto to mean frequency based color Doppler
US.
