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Introduction to Ultrasound Physics
Vassilis Sboros
Medical Physics and Cardiovascular SciencesUniversity of Edinburgh
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Transverse waves
•Water remains in positionDisturbance traverse producing more wave along the pathDisturbance travel at 90o of water movement, hence transverse
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Longitudinal wave
•Particles remains in positionDisturbance travel at 0o of particle movement, hence longitudinal
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Sound-Mechanical wave
Generated by piezoelectric crystals
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Single reflection
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Sound-Mechanical wave
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Frequency
• 1Hz = 1 cycle per second• Sound 20 Hz – 20 kHz• Ultrasound > 20kHz• Diagnostic Ultrasound 1-50 MHz• Ultrasound Therapy 40kHz-1MHz
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Some definitions
• Wavelength• Phase• Velocity of sound • Acoustic impedance• Reflection• Scattering• Refraction• Absorption• Attenuation
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Wavelength λ
c : velocity of sound (ms-1)
ν : frequency (Hz)
For ctissue= 1540 m/s cair = 330 m/s
ν=1MHz, λ=1.54mm λ=0.33mm
ν=3MHz, λ=0.51mm
ν=10MHz, λ=0.15mm
νλ c=
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Phase
a) Angle of cycle rotation
b) Phase difference between identical waves
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Pressure
• Positive – compression, negative –rarefaction
• Units 1 Pa = N / m2
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Intensity (time)
Units W / m-2
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Velocity of sound c
κ : stiffness (Pa)
ρ : density (Kg/m3)
ρκ=c
cair = 330 m/s
cwater= 1480 m/s
ctissue= 1540 m/s
cfat = 1450 m/s
cblood= 1570 m/s
cbone= 3500 m/s
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Acoustic impedance Z
cu
pZ ρ==
p : pressure (Pa)
u : particle velocity (m/s)
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Reflection
2211
2211
21
21
1
2
cc
cc
ZZ
ZZ
p
p
ρρρρ
+−=
+−=
pmuscle/ pblood= 0.03
pfat / pmuscle= 0.10
pbone/ pmuscle= 0.64
pmuscle/ pair = 0.99
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Reflection
a) Smooth surface
b) Small particle
c) Rough surface
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Scattering
General case for reflection
λ >> particle size = Rayleigh scattering
λ ~ particle size = Mie scattering
λ << particle size = reflection
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Refraction
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AttenuationAttenuation = scattering + absorption
Absorption = conversion to heat
Intensity decays exponentially
Frequency dependant
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Interference
a) Constructive interference – waves in phase
b) Destructive interference – waves in antiphase
Multiple ultrasound sources
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Plane disk transducer
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Intensity (space)
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Frequency Spectrum
a) Time domain
b) Frequency domain (FFT)
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Nonlinear propagation
At high ultrasound pressure• Time domain –
asymmetrical pattern
• Frequency domain (FFT) –Harmonic frequencies
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Bibliography
• McDicken W.N. Diagnostic Ultrasonics Churchill Livingstone New York
1991.
• Barnett E., Morley P. Clinical Diagnostic Ultrasound Blackwell
Scientific Publications, Oxford 1985.
• Meire H.B., Cosgrove D.O., Dewbury K.C., Farrant P. Clinical Ultrasound a comprehensive text: Abdominal and General Ultrasound Vol.2 Churchill Livingstone New York 2001.
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The Engineering of
Ultrasound Imaging
Vassilis Sboros
Medical Physics and Cardiovascular Sciences
University of Edinburgh
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Transducer Engineering -
Piezoelectric materials
• Positive Voltage = compression
• Synthetic ceramic - Lead Zirconate Titanate (PZT)– High sensitivity
– High acoustic power
– Easy to micromachine
– Impedance 20x tissue
• Thickness = λ/2 - resonance– Resonance due to internal reflection
– Determines transmit frequency
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Transducer Engineering –
Backing layer
• PZT Impedance 20x
tissue
– Duration of pulse difficult
to control due to internal
ringing
• Backing layer = absorber
– High impedance
– Reduces ringing
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Transducer Engineering –
Matching layer
• PZT Impedance 20x tissue
– Only 20% of energy transmitted to tissue
• Matching layer = impedance matching
– Impedance lower than PZT and higher than tissue
– Remove some ringing
• 1 layer 2x sensitivity
– λ/4 thickness
– Constructive interference towards tissue
– Destructive interference towards PZT
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Transducer Engineering –
Frequency bandwidth vs sensitivity
• High sensitivity = specific dimensions for Backing, PZT and Matching layers
– Frequency band is narrow
– Resolution low
• >1 Matching layers
– Decreasing impedance
• Bandwidth 2x (60% to 120%)
– Little loss in sensitivity
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1D – Single Plane disk transducer
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2D beams – Array transducers
a) Linear
b) Curvilinear
c) Trapezoidal
d) Sector
e) Radial
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Transducer Engineering –
Lens
• Single element
– Focus has high sensitivity and resolution
• Linear Array
– Electronically in scan plane
– Only in elevation plane
• Phased Array
– Mild in scan plane
– Stronger in elevation plane
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Linear Array Transducers
• 128 elements
– Binary processing
• Choice of frequency
– Penetration vs resolution or attenuation vs frequency
• Dimensions ~ 1/f
– ~1.3λ width per element (83mm @3MHz)
– ~30λ height - elevation(15mm @3MHz)
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Linear Array Transducers
• Active group of elements
– Finite beam per element
– Transmit fixed (~20)
– Receive (<20 to >20 as depth increases)
– Electronic focus
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Linear Array Transducers
• Transmit Electronic Focus
– Transmission timing
– One focus
– Controllable
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Linear Array Transducers
• Receive Electronic Focus
– Electronic delay
– Depth ~ element number
– Multiple foci
– Not controllable/automatic
– High resolution at all depths
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Linear Array Transducers
Transmit Multiple focus
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Linear Array Transducers
1.5D array
for improved elevation focus
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Linear Array Transducers
Transmit Apodization
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Curvilinear Array Transducers
• Sector scanning
– Wider field
– Linear array structure
– Active element number reduced -Poorer resolution
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Phased Array Transducers
• Sector scanning
– Narrow acoustic window
• Narrower elements
– All elements used (transmit and receive)
– Shorter near field per element
– Wider far field per element
– Beam steering ±45o
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Linear/Phased Array Transducers
Compounding – Reduction of noise
Persistence – Reduction of frame rate
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Matrix Array Transducers
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Endocavity Array Transducers
a) Curvilinear – transvaginal
b) Curvilinear – Transvaginal, transrectal
c) Bi-plane – Transrectal(prostate)
d) Phased array –Transoesophageal (heart)
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Intravascular Array Transducers
• Curvilinear/convex 360o
• High frequency (30MHz)
• Vessel wall
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phantom
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A-mode (transmission)
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A-mode
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Eye A-mode
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B-mode scanning
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Eye B-mode
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B-mode
Formation of B-mode image
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B-mode
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B-mode
Transmit gain and power
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B-mode
Time gain compensation
(TGC)
Compensate for attenuation
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B-mode
Analogue to digital conversion
limited values – memory
binary system
sampling rate (40MHz)
digital processing
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B-mode
Digital signal Rectification Enveloping
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B-mode
Compression
Accommodate in the image
low and high echoes
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B-mode
Image memory
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B-mode
Interpolation
Linear?
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B-mode
Reading of image memory to
form display
Gray scale
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Ultrasound Imaging Modes
• Real-time 2D imaging
– Good spatial resolution
– Good temporal resolution
– Good Penetration
Heart scan
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Ultrasound Imaging Modes
• 3D and 4D
– Good spatial resolution
– Poor temporal resolution
– OK Penetration Foetal scan
Heart scan
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Doppler Ultrasound
Pete Hoskins and Vassilis Sboros
Medical Physics and Cardiovascular Sciences
University of Edinburgh
![Page 66: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/66.jpg)
Doppler ultrasound
• Principles of Doppler
• CW/PW Doppler
• Doppler systems (spectral, duple, colour) and controls
• Principles of contrast imaging
![Page 67: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/67.jpg)
Doppler effect
![Page 68: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/68.jpg)
patient
Doppler system
Controls
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Doppler effect
Change in pitch is proportional to speed of source
Change in pitch = fS - fO
Doppler shift = fd = fS - fO
Speed = v
fd ~ v
![Page 70: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/70.jpg)
Doppler ultrasound
T
R
TransducerBlood
R
Transmission
Scattering
Reception
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Case 1. Blood stationary
T
R
R
Transmission
Scattering
Reception
fr = ft
![Page 72: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/72.jpg)
Case 2. Blood moving away from transducer
T
R
R
Transmission
Scattering
Reception
fr < ft
![Page 73: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/73.jpg)
Case 3. Blood moving towards
transducer
T
R
R
Transmission
Scattering
Reception
fr > ft
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General case
v
fr = ft + fd
ft
fd = 2 ft v/c
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Some values
• Transmit frequency 4 MHz
• Speed of sound 1540 m/s
• Speed of blood 1 m/s
• Doppler shift = 5194 Hz
• Hear Doppler signal
![Page 76: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/76.jpg)
Doppler ultrasound
Transmission Scattering Reception
ftfr
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Doppler ultrasound
θ v
ft
ft + fd
fd = 2 ft v cos θ/c
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Cosine function
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40 50 60 70 80 90
Angle (degrees)
Co
sin
e
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80ο 40ο60ο
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Some more values
• Transmit frequency 3-5 MHz
• Velocity 0-3 m/s
• Angle 40-80 degrees
• Speed of sound 1540 m/s
• Doppler frequency shift 0-15 kHz
• Audio range 0-20 kHz
• Can hear Doppler shift frequencies
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Doppler systems
• Spectral display
• Colour flow
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Spectral display
Frequency
shift (kHz)
Time (s)
baseline
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Colour flow
![Page 84: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/84.jpg)
‘Triplex’ display
![Page 85: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/85.jpg)
Summary of systems and main controls
• 2 main types of system are
– Spectral Doppler
– Colour flow
• main controls for spectral Doppler adjust:
– position of sensitive region
– beam direction
– spectral Doppler display
• main controls for colour flow adjust:
– size and depth of colour box
– beam direction
– colour display
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Spectral Doppler
Frequency
shift (kHz)
Time (s)
baseline
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Spectral Doppler - continuous wave (CW)
TR
Sensitive region
Transducer
Doppler signal
processor
Display
• Separate transmit and receive
elements
• Emits ultrasound continuously
• Receives ultrasound continuously
• Doppler signals from sensitive region
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Stand alone CW Doppler system:
features
• No B-mode image
• No depth discrimination
• Use for vessels at defined location
• Use for vessels with characteristic waveform shapes
• Obstetric applications - umbilical arteries
• Peripheral vascular application - carotid, lower limb
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CW spectral Doppler examples
Arcuate artery External
iliac
Internal iliac Umbilical
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2 vessels in beam
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Pulsed wave (PW) Doppler systems
Gate depth
Gate length
Sensitive
region
Doppler signal
processor
Display
• Emits ultrasound in pulses
• Depth discrimination
• Sensitive region depth and length set by user
![Page 92: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/92.jpg)
Stand alone PW Doppler system - features
• No B-mode image
• Depth discrimination
• Use for vessels at defined location
• Use for vessels with characteristic waveform shapes
• Transcranial
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Duplex system
B-mode + PW Doppler = Duplex
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Duplex system - features
• B-mode and PW Doppler
• depth discrimination
• all cardiovascular applications
• basis for all modern Doppler systems
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System components and signal processing
TR
Doppler signal
processor
Display
Tissue
BloodTissue
Blood
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Received signal
Frequency (MHz)
4.999 5.000 5.001 5.002
Am
pli
tud
e
From
tissue
(Clutter)
From
blood
TR
Tissue
Blood
Blood
Tissue
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Frequency (Hz)
-1000 0 1000 2000
Frequency (MHz)
4.999 5.000 5.001 5 .002
Am
pli
tud
e
Demodulation
Demodulation removes
underlying transmit frequency
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Frequency (Hz)
-1000 0 1000 2000
Filter frequency
thresholds
Lost blood
signal
-1000 0 1000 2000
High pass filter
Filtering removes the
clutter signal
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Time
Amplitude
10ms
Time
Doppler
frequency
Spectrum analysis
Spectrum analysis
estimates all the
frequencies present
in the Doppler signal
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Transducer
Display
Spectrum analysis
Demodulator
High pass filter
Signal processor
Frequency
(MHz)4.999 5.000 5.001 5 .002
-1000 0 1000 2000
Received signal
Doppler signal
Spectral display
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Cut-off filter
Filter low
Filter high
End diastolic
flow
Loss of end
diastolic flow
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Typical filter values
• Obstetrics 80-100Hz (little arterial movement)
• Vascular 150-200 Hz (some arterial pulsation)
• cardiology 300Hz+ (valves and myocardium)
![Page 103: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/103.jpg)
Pulsed wave (PW) Doppler
Gate depth
Gate length
Sensitive
region
Doppler signal
processor
Display
![Page 104: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/104.jpg)
CW
PW
Doppler signal
![Page 105: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/105.jpg)
Aliasing
• Upper limit to detected velocity measured using PW
Doppler
Max Doppler
frequency shift
![Page 106: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/106.jpg)
CW Doppler signal
PW Doppler signal
(lots of samples)
PW Doppler signal(2 samples/wavelength)
PW Doppler signal
(not enough samples)
Aliasing
![Page 107: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/107.jpg)
Aliasing
• Doppler frequency shift estimated correctly when:
– at least 2 samples per wavelength
– prf > 2 fd
• Maximum Doppler frequency shift which can be
estimated is half the prf
– fd(max) = prf/2
![Page 108: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/108.jpg)
Waveforms in disease
• Local disease (Atherosclerosis)
• Downstream disease (placental disease)
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Jet TurbulenceAtherosclerosis
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Quantification 1. Peak velocity
Max velocity
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Measurement of blood velocity I.
Transducer
v
θ v = c fd
2ft cos θ
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Measurement of blood velocity II.
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Measurement of blood velocity III.
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Standard table
Diameter Peak systolic
stenosis (%) velocity (cm/s)
0 < 90
0 - 15 < 100
15 - 50 < 125
50 - 80 > 135
80 - 99 > 230
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Downstream disease
Fetus Placenta
Uterine artery
Spiral/arcuate
arteries
Abnormal placental development leads
to increase in resistance to flow
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Umbilical waveforms
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Quantification 2. Waveform shape.
Max
Mean
Min
Resistance index (RI) = (max-min)/max
Pulsatility index (PI) = (max-min)/mean
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Estimation of RI
End diastolic marker
Peak systolic marker
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Controls for CW, PW and duplex
– position of sensitive region (PW, duplex)
• gate length, gate depth
– beam direction (PW, duplex)
• Beam steering angle
– spectral Doppler display (CW, PW, duplex)
• gain
• Filter level
• Velocity scale
• Time scale
• Baseline
– Measurement (duplex)
• Beam-vessel angle
![Page 120: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/120.jpg)
Colour flow
![Page 121: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/121.jpg)
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Colour flow image
• Display of 2D flow image superimposed on B-mode
image
![Page 124: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/124.jpg)
Colour boxes
• Image built up line by line
• Each line consists of adjacent sample volumes
Sector Linear array
Colour
boxColour
box
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Colour flow system components
Colour flow
processor
Display
Beamformer
B-scan
processor
Spectral Doppler
processor
Transducer Transmitters
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DemodulatorClutter
filter
Doppler
statistic
estimator
Post
processorBlood tissue
discriminator
Colour flow processor
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Clutter filter
clutter
blood
Frequency (MHz) Frequency (MHz)
![Page 128: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/128.jpg)
Frequency estimation
• Fast Fourier Transform (64-128 data points)
– full frequency spectrum
• Autocorrelator (3 data points)
– mean frequency
– variance
– power
![Page 129: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/129.jpg)
Post-processor
High persistence
Value =
0.4 frame 1
+ 0.3 frame 2
+ 0.2 frame 3
+ 0.15 frame 4
+ 0.10 frame 5
Low persistence
Value =
0.6 frame 1
+ 0.4 frame 2
• ‘Persistence’ or ‘Frame-averaging’
– Reduces noise
– ‘lag’ in image
![Page 130: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/130.jpg)
Blood-tissue discriminator
B-mode
image
Colour
image
(mean
Doppler
frequency)
![Page 131: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/131.jpg)
Blood-tissue discriminator
B-mode
image
Colour
image
(mean
Doppler
frequency)
![Page 132: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/132.jpg)
No blood tissue discriminator
![Page 133: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/133.jpg)
With blood tissue discriminator
![Page 134: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/134.jpg)
Colour modes
Colour
processor
Mean frequency Power
Variance
Colour Doppler Power Doppler
![Page 135: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/135.jpg)
Mean frequency: red-blue scale
![Page 136: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/136.jpg)
Mean frequency + variance: red-blue +
green
![Page 137: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/137.jpg)
Power: no B-mode in colour box
![Page 138: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/138.jpg)
Power: with B-mode in colour box
![Page 139: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/139.jpg)
Angle dependence
θ θ θ
![Page 140: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/140.jpg)
Colour Doppler angle dependence
![Page 141: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/141.jpg)
Power Doppler angle dependence
![Page 142: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/142.jpg)
Angle dependence
Doppler frequency
Doppler amplitude40o
90o
60o
Clutter filter
![Page 143: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/143.jpg)
Angle dependence
![Page 144: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/144.jpg)
Aliasing
![Page 145: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/145.jpg)
Doppler frequency
Doppler
amplitude
1m/s 2m/s 3m/s4m/s3m/s
Aliasing
limit Aliasing
limit
Aliasing
![Page 146: Medical Physics and Cardiovascular Sciences University of ...Ultrasound+Physics-p-978.pdf · Introduction to Ultrasound Physics Vassilis Sboros Medical Physics and Cardiovascular](https://reader035.vdocuments.net/reader035/viewer/2022062918/5eddcaa9ad6a402d6668fc54/html5/thumbnails/146.jpg)
Jet
Recirculation