1Kiev, Ukraine. 2016
2
Physical Principles of Modern
Medical Ultrasound Diagnostics
Barannik E.A.
Dept. of Nuclear and Medical Physics
School of Physics and Technologies
Karazin Kharkiv National University
Kiev, Ukraine. 20161804
3
A few important innovations in ultrasound imaging and their
corresponding technology enablers
HISTORY
Thanks to
its real time capabilities
its non ionizing properties and
its low cost
ultrasound has significantly impacted clinical segments
within radiology, obstetrics, vascular or cardiology etc.
Microprocessor DSP (digital signal
processing chips)
Low cost A/D
convertersMiniaturization Multicore CPU
4
CONVENTIONAL 2D IMAGING
Each focused beam allows the reconstruction of one image line
The time to build image
Maximum frame rate HzTFRimage
601
max
linesimage N
c
z=T
2
Transmitting: no dynamic focusing Receiving: dynamic focusingP
iezo
ele
ctr
ic
ele
men
ts
S
Receiv
ed
sig
nalsS
ign
al d
ela
ys
Scattere
r
Beam
form
er
Imaged
areaImaged
area
Imaged
areaImaged
area
Lateral
resolution
Final
image
5
Brightness mode (B-mode): the traditional ultrasound wave is used to image
in gray scale the structures differing by reflection power in accordance with an
amplitude of ultrasound response.
Controlled attenuation parameter (CAP): a novel technology of ultrasonic
attenuation measurement for the evaluation of some liver deceases.
B-MODE & CAP
The set of points having the same reflection power but different depth defines
the attenuation coefficient.
2
11 ln)2(P
Pd
Attenuation coefficient
6
COMPOUND B-MODE IMAGING
Speckle reduction by an averaging
of a number of equivalent, but not
correlated, images obtained using
different data sets(thyroid gland)
D-mode image formation and
speckle-noises reduction using
angle and frequency compounding
(liver)
• Angle compounding
• Frequency compounding
• Spatial compounding
• Temporal compounding
Averaging process will lead to some
loss of time and spatial resolution
7
SYNTHETIC APERTURE IMAGING
The retrospective transmit focalization can be done dynamically for each pixel
increasing the quality of the final image compared to physical insonification.
Maximum reachable frame rates increase from 30 Hz to more than 300 Hz.
Ultrafast coherent plane wave compounding. Continuous transmit focus: Ultra high resolution
Conventional transmit focus
Pie
zoele
ctr
ic
ele
ments D
ela
yed s
ignals
Sig
nal dela
ys
Scattere
r
Sig
nal genera
tor
Imaged
areaImaged
area
Imaged
area
Final
image
8
HARMONIC IMAGING
Tissue Harmonic Imaging frequently reduces
significantly image artifacts and provides
better contrast resolution
Fundamental frequency
1860
Riemann G. F. B.
Second harmonic
2)( PP
2PP + =
22P
In most medical applications it cannot be
assumed that the linearity condition is satisfied
xv
A
Bcc )
21(
0
,)(2
0000c
PA
0
2
2
002
2
2
0)()(
cPB
9
DOPPLER IMAGING
Ultrasound Doppler is widely used in clinical practice to study the vascular
system, to determine blood flow velocity and direction, and to image soft tissues
The most common imaging formats:
Color Flow Imaging
Color Power Imaging
Spectral Doppler
Doppler spectral width depends on:
wavelength
Doppler angle
sample volume size
mean flow velocity
acceleration of blood flow
velocity profile within sample volume
flow turbulence
time window duration
cos2 V
=fD
V
Doppler frequency
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CFI & CPI
Color Flow Imaging (CFI) – value and direction of velocity, color-coded and
superimposed on the B-Mode image
Color Power Imaging (CPI) – the intensity of the Doppler signal is related to
the number of moving reflectors, color-coded, superimposed on the B-mode
image, generally very sensitive for low flow
Zone sonography
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SPECTRAL DOPPLER
In the case of low mean flow velocities the width of the resulting Doppler
power spectrum is defined mostly by the wavelength of the incident field, the
Doppler signal duration and the acceleration of scatterers
In the opposite case the size of sample volume and the value of velocity
itself are much more essential
Doppler spectrogram
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M-MODE IMAGING
The pulse wave propagation is a diagnostic tool already used by the Greeks in
the 4th century BC and remarkably developed for two millennia by the Chinese.
Predictor of the cardiovascular risk: arterial wall stiffness.
Two points of the carotid artery wall have the same displacement with a
time shift . The velocity of the pulse wave is and characterizes
a wall artery stiffness.
t txC
Motion mode (M-mode)
Precise Doppler measurement of the carotid artery wall motion
TISSUE ELASTICITY
P
P P
P
P
P
P
PP
h
Δh
– bulk modulus (ΔV ≠ 0)
– shear modulus (ΔV = 0)
– compressional Young’s modulus
compressional wave velocity
shear wave speed
compressional Young’s modulus
K
μ
E
,3μεPE
ρKc
ρμct
hΔhε Tissues Е, kPa
Breast
normal fat 18-24
normal grandular 28-66
fibrous tissue 96-244
carcinoma 22-560
Prostate
normal anterior 55-63
normal posterior 62-71
BPH 36-41
carcinoma 96-241
Livernormal 0.4-6
cirrhosis 15-100
The relative range of values between
deferent soft tissues for the shear modulus
is several orders of magnitude greater than
that for the bulk modulus
14
Simply operated by lightly pressing a probe to the surface of the body, the
hardness of tissue can be displayed color in real-time.
Compression elastography is not quantitative method.
COMPRESSION ELASTOGRAPHY
Cross-correlation-based
tracking algorithms of
movement detection
B-mode CE-mode
15
Acoustical streaming in the water starch solution and shear wave in elastic
media like tissue, which were induced by the acoustic radiation force.
ACOUSTIC RADIATION FORCE
If sufficient energy if applied at the focus of an ultrasound beam, tissue can
be remotely pushed in the direction of the ultrasound wave propagation. A
transient shear wave that propagates transversally is generated.
Acoustic radiation force: , - temporal average intensityTA
Ic
αF
2
TAI
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SHEAR WAVE EXCITATION
Shear waves are amplified in a
Mach cone shape (in yellow), which
increases the propagation distance
of shear waves while minimizing
acoustic power
Wavefront
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SHEAR WAVE SPEED
Frequency-domain Form of Wave Equation
Artannlabs & Supersonic Imagine (France)Karazin KhNU & Ultrasign (Ukraine)
Two-dimensionalOne-dimensional
0),(
),(2
222
x
xu)
ρ
ηiω(cxuω
t
0
),(2
x
xu)
ρ
ηiω(ciωu(ω,x)
t
Karazin KhNU & Artannlabs (USA)
STCU #865, #865(C), P-150
u(yn-1,t)
u(yn,t)
u(yn+1,t)
t
Tissue displacement in points with different radial coordinate in the focal plane
allows defining of the first and second derivatives for shear speed estimation.
18SWEI gives important quantitative information on the elastic
properties of tissue and improves cancer diagnostic
Breast: red – cancer, blue – no cancer
Abdominal cavity: soft
tissue metastases
SHEAR WAVE ELASTICITY IMAGING
(SWEI)
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MULTI-MODALITY IMAGING
True image of breast phan-
tom: gray – no cancer,
red – cancer
Compound image: gray–
no cancer, red – cancer,
green – future cancer
Electrical impedance tomography
Inverse scattering –
acoustic absorption
Transmission tomo-
graphy – speed of
sound
Feature space
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Thank you for attention!