presentation-kim-bredahl-doppler-ultrasound.pdf

Vascular Ultrasound
Kim Kargaard Bredahl, MD, Ph.D

Background
• Resident in vascular surgery
• Vascular ultrasound on a daily basis
– Stenosis
– Flow measurement
– Aneurysms (size)
• Ph.d thesis 3D and contrast-enhanced ultrasound in AAA and
endovascular aneurysm repair surveillance
– Size and flow detection
• Course in European Society of Vascular surgery
– Basic course
– Advanced course
kimbredahl79@gmail.com

Goals of this lesson
• Achieve basic knowledge of vascular ultrasound and
the machinery
• Understand the concept of colour Doppler and
Doppler spectrum
• Be able to perform flow measurement and know the
related pitfalls
• Know how to use and handle ultrasound contrast
• Practical tips for doing ultrasound
• Hands on session is possible from 1400 in Dept. of
Vascular Surgery: Located on 11th floor, entrance 3,
central building. kimbredahl79@gmail.com

Ultrasound in vascular surgery
Size
- Aneurysms
Flow detection
-Leakage
-Receptor artery
for bypass
Morphologic and Dynamic flow visualization in human or animals
Volume flow
- Dialysis
Contrast
-Plaque or
thrombus
evaluation
-Neovasc.
Research area
Velocities
Flow Pattern
- Stenosis

Vascular ultrasound
• Real time imaging
– Can be repeated and is harmless
– Dynamic information
– Morphology
• Pitfalls
– Operator dependent
• Demonstrate and report your variabilty
– Bland Altman plots

Ultrasound imaging – What can be displayed
Brightness mode (B-
mode) also called grey-
scale imaging
-Morphology
Colour
Spectral analysis
Doppler Ultrasound - Dynamics

Brightness-mode
Machinery
CD Player – do you
remember it? Receiver Loudspeaker
Amplification
Raw data

Ultrasound equipment in short – two unit
model
Transducer
Mechanical
energy
Filtered and amplified
Received
information
Displayed
Tissue

Brightness depends on
-Output power
-Attenuation
-Scattering
-Acoustic impedance
-Amplification of the
returning signal called
gain
Skin
Depth
B-mode
Two ways to increase signal intensity
1. Increase output power, which for safety
reasons is fixed.
2. Increase amplification, which is the gain
level (2D)
Amplifier
Filter
Screen
Mechanical
energy
Receiving
element
Transmitting
element
Output power
Electric
energy
Tissue
Tissue
related
Brightness mode (B-mode)

Small adjustments to increase the image quality – focal zone
Superficial focal zone

• Worst images:
ultrasound beam is
parallel to the interface
•
Best images: ultrasound
beam is perpendicular
to the interface
• interface
From sound to image Operator dependent
factors B-mode
Clear definition of the arterial walls is a good indication of perpendicular position.

Heavily calcified arterial Aortic anterior wall
Don’t blame the operator

Brightness-mode – 3 buttons!!!
Raw data
Volume = gain →2D button
Optimal gain level = some
echo signal insight the
vessel

Brightness-mode 2. and 3. button
Adjust the depth of your
scanfield
Region of interest:
at least 1/3 of the
scan field
If you can get close it is
good ☺

Transducer
Image
resolution
Penetration
High-frequency
Superficial structures

Transducer
Low-frequency
Deep
Structures

From sound to image
Superficial imaging:
High frequency low penetration but better
image resolution
Depth of penetration depend on frequency.
Abdominal imaging:
Low frequency high penetration – Your
neighbour’s bass is more clearly than the
treble
The lateral image resolution is poorer
than the axial image resolution due to
higher density of scan lines
Linear array
9 MHz
17 MHz
3-5 MHz
Curved array
Transcranial or cardiac imaging:
Large field of view compared to the
size of the transducer face.
Electronical steering
Phased array

3-D transducer Real time biplane imaging
Pixels total: Scan field
Dimensions are known
Pixels outside the
segmentation
Pixels inside = AAA

Transducer
High-frequency Low-frequency
- Marking on the left by your thumb
- Towards the heart or cranial (carotid)

Transducer
Handheld Fingercontrol

Tasks for practical session later today
• B-mode optimization –
– Gain
• A little echo-signal inside the vessel
– Depth
• The region of interest should occupy 1/3 of the display
– Focus
• On the far wall.

Doppler effect
”the Doppler shift”

Spectral analysis
Flow towards the transducer will
displayed as positive
Flow away from the transducer will displayed as
negative
Tim
e
Linear velocity is
displayed on the
vertical –axis (cm/s)
Proportion of blood cells at
a particular speed along
the third axis – brightness
of the display
Vessel

Heart Foot
In this example:
Blood flow towards
the transducer is
coded red
Blood flow away
from the transducer
is coded blue
Colour Doppler
• B-mode image with
• Colour coded Doppler
signals in the steering-box

θ
Tilting or steering
Colour Doppler

Spectral analysis
Flow towards the transducer will
displayed as positive
Flow away from the transducer will displayed as
negative
Time
Linear velocity is
displayed on the
vertical –axis (cm/s)
Proportion of blood cells at
a particular speed along
the third axis – brightness
of the display
Vessel

B-mode image
+
Doppler curve
=
Velocity
is
coded
Duplex
Colour Doppler

SFA
External
Iliac artery
Remember! The Doppler shift is based on Doppler
equation where cosinus function is included, and
cosinus to 90 degree is zero
Colour Doppler
1
Cos
(θ)
Sin
(θ)
0

Scan positions
Groin or SFA Poplitea

Colour Doppler
Remember! The pulse repetition frequency is important in
order to visualize blood-flow.
Growth of a tree cannot
be observed by
watching every second!
If the speed is high – you have to watch every
second
Low
flow
PRF too high PRF too low

Display of Colour Doppler and
spectrum
Peak systolic
velocity
Mean
velocity
Framerate
Angle θ
Distance
Colour
scale
Beam path (Steer)
Colour
Box
Doppler angle
Correction curser
Doppler Angle θ
Sample Volume

Normal triphasic flow in peripheral artery
1. First phase systolic forward flow
2. Second phase diastolic flow reversal
3. Third phase diastolic forward flow
2
1
3
Blood flow in peripheral arteries
Forward and reversed flow are
seen simultaneously during the
diastolic phase
Reversal flow depends on the
peripheral resistance
After exercise
The velocity of blood cells (or Doppler shift
freq.) vary with time due to arterial pulsation
Low resistance vessel
-Organ supply

Normal Triphasic flow
After releasing the cuff
Normal Triphasic flow
Recovery of peripheral resistance

Organ supply – Low resistance
A. Mesenterica
superior

Transition from laminar to turbulent flow
Blood cells with
multiple velocities Spectral
broadening
Laminar or Parabolic flow
Disturbed flow
Turbulent flow

Triphasic signal → Disturbed flow showing
spectral broadening → Finally monophasic flow

Flow profiles in stenoses
• Velocity increase
– fluid travels faster
through the
narrow section
• Turbulence

x3
Velocity profile in arterial stenosis
Stenotic signal
Post-stenotic signal
Monofasic signal
Tri-phasic signal
Blood flow
Velocity
Decrease in diameter
50%
At 70% reduction of diameter a pressure drop
occur - and the stenosis are limiting the flow
This correspond to a 2-3 fold increase in
systolic velocity

Linear velocity
Area = π . ¼ . D²
D
Flow volume = Cross section . Linear velocity
Flow measurement

Dist 0.699 cm
TAMV 13.8 cm/s
Vol Flow 318 mL/ min
Area 0.384 cm2
Flow measurement –The display
TAMV: Time Averaged mean
velocity = Mean velocity for each
line of the sonogram averaged
over a complete cardiac cycle
Peak systolic
velocity
Mean
velocity
TAMV

Flow measurement and pitfalls
• Sample volume
• Doppler angle
• Pulse repetition frequency
• Doppler gain
• Image resolution
• Variation due to pulsation
• The right imaging plane
• Other pitfalls
Related to
linear velocity
assessment

Small sample volume: Reflection only received
from fast the fastest moving blood cells
Small sample volume: Reflection will be
received from all moving blood cells
Vol flow = 477 mL / min
Vol flow = 318 mL / min
Sample volume and
Linear velocity

fd = f0 – f1 = (2 x V x f0 x cos) / C
When calculating the velocity (V)
the angle estimation is very
important – especially when  > 60.
Example:
Overestimating the angle by 5
• at 40  leads to an error of 7%.
• at 75  leads to an error of 47% !
Conclusion: Keep the angel < 60  !
30 60 80
0
10
100
Error in velocity %
Degrees
Doppler angle θ

Volume measurement - Doppler gain
High gain → overloading of the
instrument → poor direction
discrimination
Mirror image
PSV and TAMV increase
Ideal image
PSV and TAMV decrease
Too low gain → flow
may not be detected The ideal gain level

Cross section
The error is 0.084 cm or
less than 1 mm. or 11 %
Area = π . ¼ . D²
The corresponding failure in
vol flow is 21 % going from
459 mL to 362 mL

Diameter assessment and Image resolution
L9-3 MHz L17-5 MHz
Intima
No intima
For superficial structures take the transducer with the highest frequency available

Diameter assessment – when to measure
Cardiac cycle

Cardiac cycle
Upper LoA =4.7 mm
Average 1, 94 mm

Challenges in systoly
Diameter
forskel
Tid
1 sekund
Frame rate = 18
By Henrik Sillesen

Cursor position
2-6 mm. Difference!

Diameter assessment – where to measure
Taken the concept of acoustic
impedance into account the ideal
measurement would be from the
most reproducible measurement
is from leading edge adventitia
ant. wall to leading edge
adventitia posterior wall
The most reproducible
measurement
The true volume flow
From intima to intima

Karvæggen
Leading edge
of intima
Tunica media
Leading edge of adventitia –
anterior wall
Lumen
Grænsen mellem
tunica media og
tunica adventitia

Cursor position
Leading edge of intima
Leading edge of adventitia

Cursor position

Volume flow and other pitfalls
Not all vessels are circular
Most scanners assume the mean
Velocity of sound is 1540 m/s
→Systematic underestimation of the
Diameter
Medium Speed (C)
(m/s)
Air 330
Water 1480
Blood 1570
Fat 1450
Muscle 1580
Bone 3500
Soft tissue
(average)
1540

Ultrasound Contrast media
• Microbubbles ≈ Red blood cells.
– Small enough to pass through the capillaries
– Large enough to retain in the vascular system
• Blood pool agent → Indicator dilution principal with a wah
– Completely pulmonary eliminated
Gas SF6
Poor
interaction
with other
molecules
Amphophilic shell
-Stabilizes the gas
-Flexible molecule

Contrast specific imaging
• Insonation power
Instability → destruction
Backscatter
= Tissue Signal
Low pressure
High pressure
Oscillation
-Harmonic frequency
-Specific signals
≠ Tissue signal

Contrast specific imaging
• In summary
– Specific echo signal different from tissue
• No tissue signals
• No movement artifacts and blooming effects
– Independent from blood flow velocity
• No angle dependent color display
• Better spatial resolution
• Detect low flow
– Good safety profile
• No burden for the liver or kidneys
• Allergic reactions are rare

In practice
• High end scanner with a contrast specific
application
• SonoVue
– 20 gauge cannula
– Forward injection in a cubital vein.
– 1-2 ml.
– Last 6 hours after mixture.
– Anti-histamin and adrenalin.

Contrast-enhanced ultrasound
• If microvascular perfusion is important.
– Diabetic patients
• If luminal morphology is important
– Plaque size and neovascularization
– Thrombus size estimation
– Near occlusion / complete occlusion
– Flow detection

Microvasculature
C. Greis / Ultrasound contrast agents as markers of vascularity and microcirculation

Peripheral arterial disease
Healthy volunteer
Lindner JR, Portland, Oregon. JACC: Cardiovascular imaging 2008

Flow detection

Tasks for practical sessions
• Doppler Ultrasound
– Control colour box
• Size and position
• Steering
– Pulse repetition frequency
• Low and high – find the right level
– Spectral analysis
• Adjust size of sample volume
• Obtain Doppler angle < 60 degrees
– Extra option ”Walk the Doppler” from CFA to PFA.

Repetition - If I want to do it right☺
Field of
view
1. The right transducer: curved phased or linear array
transducer
2. Adjust your B-mode image
-Depth
-Focal zone
-Gain level
3. Apply colour Doppler image
-Tilt the transducer or adjust steering level
-Pulse repetition frequency level

Repetition - If I want to do it right ☺
4. Spectral Doppler
analysis
- Parallel to flow direction
and keep the angle to the
Beam path < 60º
Beam path
Flow direction

The practical sessions
5. Be correctly seated and your right should work
independently. Don’t look down! Keep eye on the road
(Keyboard).
And your left hand is as important as your right hand.

If you want to know more
• Vascular ultrasound How, why and when
– Edited by Abigail Thrush and Tim Hartshorne
• Quantitative evaluation of microvascular blood flow
by contrast-enhanced ultrasound by C. Greis. Clinical
Hemorheology and Microcirculation 49 (2011) 137-149
• Pubmed: Eiken FL et al. Diagnostic methods for
measurement of peripheral blood flow during
exercise in patients with type II diabetes and
peripheral artery disease: a systematic review

Practical stuff

Transducer
Handheld Fingercontr
ol

Brightness-mode
Machinery
CD Player – do you
remember it? Receiver Loudspeake
r
Amplificatio
n
Raw
data

Ultrasound equipment in short – two unit
model
Transducer
Mechanica
l energy
Filtered and amplified
Received
informatio
n
Displaye
d
Tissue

Display of Colour Doppler and
spectrum
Peak systolic
velocity
Mean
velocity
Framerat
e
Angle
θ
Distance
Colour
scale
Beam path (Steer)
Colour
Box
Doppler angle
Correction curser
Doppler Angle θ
Sample Volume

Sup. Fem.
artery
Sup. Fem.
artery
If the Doppler waveform doesn’t look
right

The practical sessions
5. Be correctly seated and your right hand works
independently. Don’t look down! Keep eye on the road
(Keyboard).
And your left hand is as important as your right hand.

Contents
• The clinical use of ultrasound in vascular
surgery
• From sound to image – theory 10 min.
• Doppler effect / doppler shift
– Displaying the doppler signal
– Flow profiles
• Colour doppler
• Volume measurement
– Pitfalls
• Hands on session

Ischemic disease
• Patient’s complaint
• Objective
– Peripheral blood pressure
– Dynamic flow visualization
• Linear flow velocities
• Flow pattern

Aneurysm size or mophology
Accuracy is important
Standard protocol is pivotal
-Cardiac cycle
-Delineation of the vessel wall
-Image plan; 3D ultrasound
• Ultrasound contrast
– Morphology
• Thrombus or plaque size – delineates the
lumen/thrombus

Leakage
• Flow detection
• Ultrasound contrast
– Low flow
– Microperfusion

Ultrasound = High frequency sound that induces
local periodic displacement of particles in the medium
Transducer on
Transducer off
Displacement Depth
λ
Frequency (f) = 1/τ, number of cycles of displacements during 1 second (Hz).
Medical ultrasound scanner typically use frequencies between 2 – 15 MHz

Transducer
Piezo-electro
elements
Gel
fd = fr – ft = ( 2 x V x ft x Cos θ) / C
Receiving element
Red cells = moving source,
Transducer = stationary observer
Doppler-effect
Transmitting
element
Transducer = stationary source
Red cells = Moving observer.
θ
: Angle of insonation
C: Speed of sound in tissue (1540 m/s)
V: Velocity of blood
fr: Receiving frequency
ft: Transmitted frequency

The Doppler signal of flowing blood contains a range of
velocities (or Doppler shift frequencies)
Bloods cells near the vessel wall will move more slowly
Displaying the doppler signal
Velocity
time

Output power
Electric
energy
Transmitting
element
Receiving
element
Amplifier
Analyser
Screen
From sound to image
Transducer: Converts energy into another form of energy
Ultrasound machine interprets the receiving information
Mechanical
energy
Vibration
Tissue
High-End
Frame rate depends on
-Machine power
-Work load
Reduce field of view.
Steady patient!
Low-End
Two possibilities to
increase signal
intensity
-Increase output
power, which is
often locked
- Increase
amplification,
which is the gain
level (2D)
but at a certain
level signal ≠ noise

From sound to image:
Skin
Brightness proportional to
amplitude of echoes – grey scale
We assume the speed of ultrasound through
the tissue is constant, and we know the
generated frequency then we can predict the
distance from the source to the reflective
boundary
Medium Speed (C)
(m/s)
Air 330
Water 1480
Blood 1570
Fat 1450
Muscle 1580
Bone 3500
Soft tissue
(average)
1540
Depth
Distance = (Time . C) / 2

Output power
Electric
energy
Transmitting
element
Receiving
element
Amplifier
Analyser
Screen
From sound to image
Transducer: Converts energy into another form of energy
Ultrasound machine interprets the receiving information
Two possibilities to
increase signal intensity
-Increase output power,
which is often locked
- Increase amplification,
which is the gain level
(2D)
but at a certain level
signal ≠ noise

From sound to image
Superficial imaging:
Depth of penetration depend on frequency.
High frequency low penetration but better image
resolution
Abdominal imaging:
Low frequency high penetration – Your neighbour’s bass
is more clearly than the treble
The lateral image resolution is poorer the axial image
resolution due to higher density of scan lines
Linear array
9 MHz
13 MHz
3-5 MHz
Curved array
Cardiac imaging:
Large field of view compared to the size of the
transducer face.
Electronical steering
Phased array

Difference in acoustic impedance
determines reflection rate
From sound to image – Acoustic impedance: resistance
against passage of the sound wave
Similar acoustic impedance
• Muscle/blood (ratio=0.03)
• Fat/muscle (0.10)
• Low/moderate reflection - ideal for US
Different acoustic impedance
• soft tissue/air (ratio=0.999)
• soft tissue/bone (0.65)
• High reflection – not ideal for US imaging

Colour Doppler
ultrasound
• B-mode grey-scale image +
• Colour coded Doppler signals
in the colour-box
Blood flow towards the
transducer is (probably) coded
red
Blood flow away from the
transducer is coded blue
Arterial flow
Venous flow
Primarily used for flow detection

θ
The doppler shift depends on the angle θ
Cos (θ)
Sin (θ)
Doppler angle θ = 90 then
Cos(90) = 0
1
0

Doppler angle θ

The Doppler spectrum displays:
Time along the horizontal axis
Velocity (Doppler shift) along the vertical axis
Proportion of blood cells at a particular speed along the
third axis – brightness of the display
Displaying the doppler signal
Blue The mean velocity
Peak systolic velocity

Repetition - If I want to do it right☺
Field of view
1. Ultrasound equipment and find the on/off button
2. The right transducer: curved phased or linear array transducer
3. Adjust your B-mode image
-Depth
-Focal zone
-Gain level
4. Apply color doppler image
-Tilt the transducer or adjust
steering level
-Pulse repetition frequency level
-Doppler gain level

Repetition - If I want to do it right ☺
5. Spectral doppler analysis
- Parallel to flow direction
and keep the angle to the
Beam path < 60º
Beam path
Flow direction
6. Volume flow measurement
-The most important factor is the diameter assessment

Sup. Fem.
artery
Sup. Fem.
artery
Underestimate the true velocity Align the transducer with
reasonable length of the vessel
Out of image

6
PRF too high
PRF too low
Aliasing – Flow is going backwards
12
9 3
45 min
later
90 min
later
135 min
later
Pulse Repetition Frequency
PRF / scale
Especially low flow is
not detected

Colour Doppler ultrasound
B-mode image
+
Doppler curve
=
Duplex

Contents
• From sound to image – theory 10 min.
• Doppler effect / doppler shift
– Displaying the doppler signal
– Flow profiles
• Colour doppler
• Volume measurement
• Contrast-enhanced ultrasound

Display of Colour Doppler and spectrum
Colour
scale
Framerate
Angle θ
Doppler Angle θ
Beam path (Steer)
Colour Box
Doppler angle
Correction curser
Sample Volume
Distance
Peak systolic
velocity
Mean
velocity

Karvæggens bestanddele
Små glatte
muskelceller og
elastisk fibre
Endothelceller
Adventitia består
mest af kollagen
Stor forskel i
akustisk
impedans fra lav
til høj →
Refleksion ↑
Måler aldrig IMT på forreste
væg

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