Beginners guide to understand the concepts and techniques of Doppler USG imaging -types , technical info,subtypes ,artefacts and interpretation

1. DOPPLER PHYSICS
• Dr.Sahil
Chaudhry,
AJIMS

3. OUTLINE
• Doppler
Principles
• Pulsed
and
Con:nuous
Doppler
• Aliasing
and
Nyquist
Criteria
• Spectral
Analysis
• Colour
flow
imaging
• Power
Doppler
• Doppler
Ar:facts

5. Waves from a stationary source
Wave
peaks
evenly
spaced
around
the
source
at
1
wavelength
intervals

6. Waves from a moving source
Source
moving
this
way
Old
posi7ons
of
source

7. Doppler Effect
v Change
in
the
perceived
frequency
of
sound
emiGed
by
a
moving
source.
v The
basis
of
Doppler
ultrasonography
is
the
fact
that
refected/scaGered
ultrasonic
waves
from
a
moving
interface
will
undergo
a
frequency
shiK.

8. RECEIVED FREQUENCY TRANSMITTED FREQUENCY
DOPPLER SHIFT

9. • In
diagnos:c
ultrasound,
the
Doppler
effect
is
used
to
measure
blood
flow
velocity.
• When
the
emiGed
ultrasound
beam
strikes
moving
blood
cells,
the
laGer
reflect
the
pulse
with
a
specific
Doppler
shiK
frequency
that
depends
on
the
velocity
and
direc:on
of
blood
flow.

10. • IF RECEIVED FREQUENCY = TRANSMITTED FREQUENCY, NO DOPPLER SHIFT
¨ Posi:ve
shiK
Ø
Received
freq
>
transmiGed
freq
Ø Flow
towards
the
transducer
¨ Nega:ve
shiK
Ø TransmiGed
freq
>
received
freq
Ø Flow
away
from
the
transducer

12. • Angle
•
Cos
(a)
Doppler
shiK
depends
on
the
cosine
of
the
angle
between
the
sound
beam
and
the
direc:on
of
the
mo:on
V
=
Fd
×
C
2
fₒ
×
cos
ᶱ
Op:mal
angle
30°
-­‐
60°
Angle
Cos
theta
0
1
45
0.7
60
0.5
90
0

13. Angle
to
Flow
Angle Cosine
0 1.00
15 0.97
45 0.71
60 0.50
75 0.26
90 0.00

14. The size of the Doppler signal is dependent on:
• Blood
velocity:
as
velocity
increases,
so
does
the
Doppler
frequency
• Ultrasound
frequency:
higher
ultrasound
frequencies
give
increased
Doppler
frequency.
• Angle
of
Insona:on

15. Continuous Doppler
• Uses
two
crystals,
one
to
send
and
one
to
receive.
• Uses
con:nuous
transmission
and
recep:on
of
ultrasound.
• Doppler
signals
are
obtained
from
all
vessels
in
the
path
of
the
ultrasound
beam
(un:l
the
ultrasound
beam
becomes
sufficiently
aGenuated
due
to
depth).
• Unable
to
determine
the
specific
loca:on
of
veloci:es
within
the
beam
and
cannot
be
used
to
produce
color
flow
images.
• Used
in
adult
cardiac
scanners
to
inves:gate
the
high
veloci:es
in
the
aorta.
AUDI
O
AMP
LIFIE
R
FIL
TE
R
DEMOD
ULATO
R
OSCILLAT
OR,
TRANSMI
T
AMPLIFIE
R
RECEIV
ER,
AMPLI
FIER

16. CW
DOPPLER
• Doppler shift can be located at any depth in
the flow sensitive zone of beam.
• The Doppler receiver is unable to determine
the exact location of the Doppler shift.
• Thus CW lacks range resolution.
• Because it is continuously sample returning
echoes it have no limitations
on measuring high flow velocities.

18. Directional Doppler
ü Quadrature
detec:on
helps
in
determining
flow
direc:on.
ü Received
echo
signals
are
amplified
àsplit
into
two
iden:cal
channels
for
demodula:on.
ü The
reference
signals
from
the
transmiGer
sent
to
the
two
demodulators
are
90
degrees
out
of
phase.
ü Two
separate
Doppler
signals
are
produced.
They
are
iden:cal
except
for
a
small
phase
difference
between
them,
and
this
phase
difference
can
be
used
to
determine
whether
the
Doppler
shiK
is
posi:ve
or
nega:ve.

19. Pulsed Doppler
• The
transducer
both
sends
and
receives
the
signal.
• The
returned
signal
is
gated
so
that
only
informa:on
about
the
desired
depth
is
computed
• Pulses
–
just
like
real
:me
scanning
• Need
to
“gate”
analysis
of
received
pulse,
so
we
know
where
the
moving
objects
are.
• This
allows
measurement
of
the
depth
(or
range)
of
the
flow
site.
Addi:onally,
the
size
of
the
sample
volume
(or
range
gate)
can
be
changed.
Pulsed
wave
ultrasound
is
used
to
provide
data
for
Doppler
sonograms
and
color
flow
images
Sam
ple
Demod
ulator
Gate
size
and
depth
Master
Oscillat
or
Rec
eive
r
Gated
Trasmi
Ger

20. Continuous doppler Pulsed doppler
Ø
Separate
crystal
for
transmiqng
&
receiving
Ø
Can
measure
high
veloci:es
Ø
Range
ambiguity
Ø
Single
crystal
transmits
&
receives.
Ø
Range
resolu:on
Ø
Can’t
measure
very
high
veloci:es

21. Doppler Modes
Colour
Power
Spectral

22. Physics of Spectral Flow
Vascular
Flow
• Blood
flow
is
normally
laminar
with
velocity
decreasing
from
the
center
outward
to
the
vessel
walls

23. Hemodynamic Principles
Laminar
Flow
• Con:nuous
or
laminar
flow
is
characterized
by
a
constant
velocity
over
:me.
• The
flow
profile
of
laminar
flow
is
determined
by
iner:al
and
fric:onal
forces.
Fric:on
produces
a
laminar,
or,
in
the
three-­‐dimensional
model,
parabolic
flow
profile.
Flow
is
fastest
toward
the
center
of
a
vessel
and
decreases
toward
the
wall,
where
it
approximates
zero.
• Color
duplex
ultrasound
reflects
this
flow
profile
by
lighter
color
shades
in
the
center
(fast
flow)
and
darker
shades
near
the
wall
(slow
flow)

24. Typical triphasic Doppler waveform of the
popliteal artery.
color duplex scan depicts
laminar flow with lighter
coloring in the
center darker colors
toward the margins.

25. Pulsatile Flow
• In
contrast
to
laminar
flow,
pulsa:le
flow
changes
periodically
over
:me.
Phases
of
accelera:on
and
decelera:on
vary
in
rela:on
to
changes
in
pressure.
• The
pressure
amplitude
generated
by
the
leK
ventricle
is
reduced
by
the
compliance
of
the
aorta
and
other
large
vessels
(windkessel
effect),
resul:ng
in
a
more
steady
flow.
• Another
factor
affec:ng
the
flow
profile
is
the
peripheral
resistance
• As
the
peripheral
resistance
is
a
crucial
factor
affec:ng
the
waveform,
a
dis:nc:on
is
made
between
low-­‐
resistance
flow
and
high-­‐resistance
flow.

26. Low Resistance Flow
• Arteries
supplying
parenchymal
organs
and
the
brain
are
characterized
by
a
fairly
steady
blood
flow
as
a
result
of
low
peripheral
resistance.
In
these
arteries,
a
moderate
systolic
rise
is
followed
by
a
steady
flow
that
persists
throughout
diastole.
This
flow
profile
is
typical
of
the
renal,
hepa:c,
splenic,
internal
caro:d,
and
vertebral
arteries
• The
windkessel
effect
thus
ensures
a
more
con:nuous
flow
than
would
result
from
the
ac:on
of
the
leK
ventricle
and
aor:c
valve
alone.
As
a
result,
flow
will
become
more
pulsa:le
when
this
effect
and
the
normal
elas:city
of
the
vessels
are
lost.

27. High Resistance Flow
• A
high
peripheral
resistance
results
in
a
more
pulsa:le
flow
with
a
steep
systolic
upslope
during
the
accelera:on
phase,
followed
by
decelera:on
and
a
significant
reflux
in
early
diastole
and
short
backward
flow
in
mid-­‐diastole.
Zero
flow
is
typically
seen
in
end
diastole.
This
paGern
is
referred
to
as
triphasic
flow.
• High-­‐resistance
flow
is
typical
of
the
arteries
supplying
Muscles
and
the
skin

28. Transition from laminar to turbulent flow
Ø Turbulent
flow
occurs
when
laminar
flow
breaks
down
and
the
par:cles
in
the
fluid
move
randomly
in
all
direc:ons
with
variable
speeds
Ø
Turbulent
flow
is
more
likely
to
occur
at
high
veloci:es
(V),
and
the
cri:cal
velocity
at
which
flow
becomes
turbulent
depends
on
the
viscosity,
the
density
of
the
fluid
and
the
diameter
of
the
vessel
(d).
Reynolds
described
this
rela:onship,
which
defines
a
value
called
the
Reynolds
number
(Re)

30. Color
Flow
Imaging
•
Doppler data evaluated using
autocorrelation.
• Autocorrelation is a technique that
compare the echo from each pulse
with the echo from the previous pulse.
• Autocorrelation requires a minimum
of 3 pulses per scan line.

31. Color
Flow
Imaging
• This technique can only produce an
estimate of the mean frequency shift
and mean velocity.
• Increasing the line per frame provides
an image with more resolution at the
expense of the frame rate.

32. Color
Flow
Imaging
Color
Resolu7on
Frame
rate
Number
of
lines
in
Gray
scale
imaging

33. Color
Flow
Imaging
• To produce the color flow image, the
mean Doppler shift is encoded
according to a preset color map.
• This color information is superimposed
on the gray scale anatomic scan in real
time.

34. Color
Flow
Maps
• Velocity color map
• Variance color
map

37. .

38. Velocity
Color
Bar
Increasing flow velocity
away from the transducer
Zero flow
Increasing flow velocity
toward the transducer

39. Variance
Color
Bar
Variance
Color

40.
Near
occlusion
Total
occlusion

41. Colour Doppler
Limita:ons
:
Ø Semi
quan:ta:ve
Ø Angle
dependence
Ø Aliasing
Ø Ar:facts
caused
by
the
noise
Ø Poor
temporal
resolu:on.

42. Colour Box
Color box is an operator-adjustable
area within US image in which all
color Doppler information is
displayed.
Because frame rate decreases as
box size increases, image
resolution & quality are affected by
box size and width.
Box should be as small &
superficial as possible while still
providing necessary information.
A deep color box will result in a
slower PRF, which may produce
aliasing of depicted color flow.

43. Colour Box

44. Aliasing
• Aliasing
is
produc:on
of
ar:ficial
low
frequency
signals
when
the
sampling
rate
is
less
than
twice
the
doppler
signal
frequency.
When
the
Doppler
shiKs
exceed
a
value
Nyquist
frequency,
veloci:es
are
perceived
as
going
in
opposite
direc:on.
Aliasing
occurs
when
Doppler
shi2
>
Nyquist
frequency
Nyquist
freq
-­‐
Pulse
Repe<<on
Frequency
2

45. Nyquist
Sampling
Limit
• The
Maximum
Doppler
frequency
that
can
be
sampled
is
½
the
PRF
• Example,
if
PRF
=
8
kHz
– Max
Doppler
frequency
is
4
kHz
• Example,
if
PRF
=
4
kHz
– Max
Doppler
frequency
is
2
kHz

46. Adjustments to be made to avoid aliasing
• Increasing
the
PRF
• Moving
color
or
spectral
baseline
up
or
down.
• Decreasing
Doppler
shiK
frequency
(changing
angle
of
insona:on).
• Using
a
lower-­‐frequency
transducer.

47. Doppler
Spectrum
Assessment
Assess the following:
1. Presence of flow
2. Direction of flow
3. Amplitude
4. Window
5. Pulsatility

48. Doppler
Spectrum
Assessment
Check
for
Flow
Flow
Detected
No
Flow
Detected
Check
SV
Placement
Sensi7ve
Decreased
Sensi7vity
Improve
Sensi7vity
Check
Sensi7vity
Check
Beam-­‐
flow
angle

49. Doppler
Spectrum
Assessment
Sensitivity can be improved by:
• Increasing power or gain.
• Decreasing the velocity scale.
• Decreasing the reject or filter.
• Slowly increasing the SV size.

50. Doppler
Spectrum
Assessment
Direction of Flow
Pulsed Doppler use
quadrature phase
detection to provide
bidirectional Doppler
information.

51. Doppler
Spectrum
Assessment
Flow can either be:
• Mono-phasic
• Bi-phasic
• Tri-phasic
• Bidirectional

52. Spectral
Display
Frequency
Time
Mono-­‐phasic
Flow
Flow
on
just
on
side
of
the
Baseline.

53. Spectral
Display
Frequency
Time
Bi-­‐phasic
Flow
Flow
start
on
one
side
of
the
Baseline
and
then
crosses
to
the
other.

54. Spectral
Display
Frequency
Time
Tri-­‐phasic
Flow
Flow
start
on
one
side
of
the
baseline
side,
then
crosses
to
the
other,
then
returns
to
the
original
side.

55. Spectral
Display
Time
Frequency
Bidirec7onal
Flow
Flow
which
occurs
simultaneously
on
both
sides
of
the
baseline.

56. Doppler
Spectrum
Assessment
Amplitude
The spectrum displays echo amplitude by varying the
brightness of the display.
The amplitude of the echoes are determined by:
• Echo intensity
• Power
• Gain
• Dynamic range

57. Doppler
Spectrum
Assessment
Window
• Received Doppler shift consist of a range of
frequencies.
• Narrow range of frequencies will result in a
narrow display line.
• The clear area underneath the spectrum is
called the window.

58. Spectral
Display
Sonic
Window
Velocity
Time
A
narrow
range
of
frequencies
results
in
large
clear
window.

59. Spectral
Display
Sonic
Window
Velocity
Time
A
broad
range
of
frequencies
results
in
diminished
window.

60. Spectrum
Broadening
Loss of the Spectral window
is called
Spectral Broadening.

61. Spectrum
Broadening
Occurs usually:
• As the blood decelerates in diastole
• If sample volume is placed to close to the vessel wall
• In small vessels (parabolic velocity profile)

62. Spectrum
Broadening
• Tortuous vessels.
• Low flow states..
• Excessive gain/power/dynamic range

63. Spectrum
Broadening
It is hallmark of
disturbed and/or
turbulent flow.

64. Spectrum
Broadening
Pulsatility
• Measures the difference between the maximum
and minimum velocities within the cardiac cycle.
• Indices are unit less.
• All increase in value as flow pulsatility increases.
• Can be measured without knowledge of the Doppler
angle.

65. Spectral analysis
sharp
systolic
peak
+
reversed
diastolic
flow
(e.g.)
extremity
artery
in
res:ng
stage.
Broad
systolic
peak
+
forward
flow
in
diastole
(e.g.)
ICA,renal,vertebral,celiac.
Sharp
systolic
peak
+
forward
flow
in
diastole.
(e.g.)
ECA
&
SMA
(during
fas:ng)

66. Spectral changes in disturbed flow

67. • Doppler indices are :
Ø PI
Ø RI
Ø SYSTOLIC / DIASTOLIC RATIO
Ø Acceleration time(AT) and acceleration index(AI)
Ø SPECTRAL BROADENING
• These indices can thus serve as a semiquantitative parameter
for the evaluation of stenoses

68. Pulsatility Index
§ It is defined as the
maximum height of the
waveform, S, minus the
minimum diastolic, D
(which may be
negative), divided by
the mean height, M,
• Stenoses or occlusions
in arteries will alter the
Doppler waveform and
the pulsatility index.

69. Pourcelot’s Resistance index (RI)
§ The resistance indices, in particular the Pourcelot index,
reflect wall elasticity as well as the peripheral resistance of
the organ supplied
• In vessels with greater peripheral resistance, the Pourcelot
index is higher and end-diastolic velocity decreases.
§ It is defined as follows
where E is end diastolic velocity. The value of RI can be
calculated by the scanner and displayed on the screen.

70. Acceleration Time and Index

71. Spectral Broadening
§ There have been several definitions of spectral
broadening (SB) described over the years in an
attempt to quantify the spread of frequencies present
within a spectrum. One such definition is as follows:
§ Increased SB indicates the presence of arterial disease

72. • SPECTRAL
DOPPLER
• COLOUR
DOPPLER
Depic7on
of
Doppler
shiQ
informa7on
in
waveform
U7lize
the
Doppler
shiQ
informa7on
to
show
blood
flow
in
color

73. • SPECTRAL
DOPPLER
Advantages
:
• Depicts
quan:ta:ve
flow
at
one
site
• Allows
calcula:ons
of
velocity
and
indices
• Good
temporal
resolu:on
• COLOUR
DOPPLER
Advantages
:
Ø Overall
view
of
flow
Ø
Direc:onal
informa:on
about
flow
Ø
Averaged
velocity
informa:on
about
flow

74. Power Doppler
¨ Power
or
intensity
of
Doppler
signal
is
measured
rather
than
Doppler
shiK.
Limita:ons
:
¨ No
direc:on
/
velocity
informa:on
¨ Slow
frame
rate

75. Power Doppler
Ø A
color-­‐coded
map
of
Doppler
shiKs
superimposed
onto
a
B-­‐mode
ultrasound
image
Ø Color
flow
imaging
have
to
produce
several
thousand
color
points
of
flow
informa:on
for
each
frame
superimposed
on
the
B-­‐mode
image.
Ø Color
flow
imaging
uses
fewer,
shorter
pulses
along
each
color
scan
line
of
the
image
to
give
a
mean
frequency
shiK
and
a
variance
at
each
small
area
of
measurement.
This
frequency
shiK
is
displayed
as
a
color
pixel.

76. Power Doppler
Ø The
transducer
elements
are
switched
rapidly
between
B-­‐
mode
and
color
flow
imaging
to
give
an
impression
of
a
combined
simultaneous
image.
Ø
The
pulses
used
for
color
flow
imaging
are
typically
three
to
four
:mes
longer
than
those
for
the
B-­‐mode
image,
with
a
corresponding
loss
of
axial
resolu:on.
Ø Assignment
of
color
to
frequency
shiKs
is
usually
based
on
direc:on
(for
example,
red
for
Doppler
shiKs
towards
the
ultrasound
beam
and
blue
for
shiKs
away
from
it)
and
magnitude
(different
color
hues
or
lighter
satura:on
for
higher
frequency
shiKs).

77. Power Doppler
Advantages
:
Ø Increased
sensi:vity
of
flow
detec:on
Ø Less
angle
dependence
Ø No
aliasing
Ø Noise
–
a
homogenous
background

78. Spectral Velocity Scale
Scale
change
adjustment

79. Colour Velocity Scale

80. Spectral Baseline

81. Colour Baseline

82. Wall Filter
¨ Filters
eliminate
typically
low-­‐
frequency
high-­‐
intensity
noise
that
may
arise
from
vessel
wall
mo:on

83. Spectral Filter
Very
High
filter
Color
duplex
US
image
obtained
with
a
high
wall
filter
seVng
shows
loss
of
the
low-­‐velocity-­‐flow
component
of
the
spectral
waveform
immediately
above
the
baseline.
Higher-­‐velocity
flow
is
well
depicted,
and
accurate
flow
quan:fica:on
can
s:ll
occur.
In
the
evalua:on
of
the
liver
vasculature,
this
is
likely
to
become
relevant
only
when
flow
velocity
is
very
low
and
falls
within
the
range
of
veloci:es
that
are
filtered
out.

84. Spectral Filter
Color
duplex
US
image
demonstrates
how
the
spectral
waveform
progressively
fills
in
toward
the
baseline.
Op:mal
filter
50-­‐100
Hz

85. Colour gain
Amplifica:on
of
the
sampled
informa:on

86. Spectral gain

87. Angle Correction
• Angle
correc:on
refers
to
adjustment
of
Doppler
angle
&
is
used
to
calibrate
velocity
scale
for
the
angle
between
US
beam
and
blood
flow
being
measured

88. 45’’
0’
>90’
• The
angle
of
insona7on
should
also
be
between
45°-­‐
60°.
• Flow
may
appear
to
be
reversed
when
the
beam-­‐flow
angle
changes
about
90°.
• Complete
loss
of
flow
may
be
evident
when
the
beam-­‐flow
angle
is
90°.

89. Beam Steering
45°
’
>90°

90. Gate Size
Represents the area of flow
assessed with Doppler.

91. Sample Volume
Sample volume size should be 1/3 of
the diameter of the vessel.

92. Inversion
¨ Ability
to
manually
invert
the
spectral
wave
or
color
seqngs.

93. Colour Inversion

94. Spectral Inversion

95. Doppler artifacts
• Aliasing
• Mirror
image
• Blooming
• Color
in
non
vascular
structures
• Twinkle
ar:facts

96. Mirror
image
ar:fact
• any
vessel
adjacent
to
a
highly
reflec:ve
surface,
such
as
the
lung,
subdiaphragma:c
region
of
the
liver
and
the
supraclavicular
region

97. Blooming artifact

98. Twinkling artifact
Rapidly
fluctua:ng
mixture
of
Doppler
signals
(red
and
blue
pixels)
that
imitate
turbulent
flow

99. Colour in non vascular structures (Colour flash
artifact)
•
Manifests
as
a
colour
signal
due
to
transducer
or
pa:ent
mo:on
• Hypoechoic
areas
such
as
a
cyst
or
a
duct
are
suscep:ble
to
colour
flash
ar:fact.