bym504e-mk-basics of ultrasound imaging
TRANSCRIPT
Basics of Ultrasound ImagingMustafa Karaman, PhD 1
Basics of Ultrasound Imaging
April 2014
Department of Electronics & Communications Engineering,
Istanbul Technical University, Istanbul, Turkey
Mustafa Karaman, Ph.D
Basics of Ultrasound ImagingMustafa Karaman, PhD 2
Ultrasound B-Scan Image: Liver
Basics of Ultrasound ImagingMustafa Karaman, PhD 3
Pulse-Echo Ultrasonic Imaging System
Basics of Ultrasound ImagingMustafa Karaman, PhD 4
Ultrasonic Imaging
• Tissue-wave interaction
• Transducer design
• Analog and digital electronic design
• Array signal processing (beamforming)
• Signal and image processing
Basics of Ultrasound ImagingMustafa Karaman, PhD 5
Acoustic Applications
– Medical Imaging (non-invasive diagnosis)
– Nondestructive testing (NDT)
– Underwater acoustics (sonar)
Basics of Ultrasound ImagingMustafa Karaman, PhD 6
Medical Imaging
– non-invasive observation of internal structures
of human body
Based on interaction between tissue &
energy (x-rays, electric fields, ultrasound, etc.)
Different forms of energy/radiation
imaging of different characteristics of tissue
Basics of Ultrasound ImagingMustafa Karaman, PhD 7
Medical Ultrasound
– represents mechanical properties of tissue
– has no harmful biological side effect
– allows real-time imaging
– offers small-size, low-cost systems
complementary diagnostic tool
+ (will) provide real-time 3D imaging
Basics of Ultrasound ImagingMustafa Karaman, PhD 8
Medical Ultrasound Waves
– Longitudinal waves: 2-15 MHz
– Transverse waves
» high attenuation in tissue
not used
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Basics of Ultrasound ImagingMustafa Karaman, PhD 10
Basics of Ultrasound ImagingMustafa Karaman, PhD 11
Ultrasound Parameters
water
fat
bone
liver
kidney
muscle
soft tissue
Speed
(m/s)
1480
1440
4080
1550
1560
1590
1540
Attenuation
(dB / MHz cm)
0.0025
0.56
12.0
0.95
1.1
1.8
0.81
Impedance
1.48
1.36
7.80
1.66
1.63
1.71
1.62
)/10( 26 smkg
Basics of Ultrasound ImagingMustafa Karaman, PhD 12
Ultrasound Parameters
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Frequency & Wavelength
f
c
In soft tissue: C = 1540 m/s
f
(MHz) (mm)
3.0 0.51
5.0 0.31
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Reflection
2
12
122
ZZ
ZZPower reflection coefficient:
Reflection between X and Soft tissue Z = 1.62
X 2
water + 0.452 0.020
fat + 0.087 0.008
bone - 0.656 0.430
liver - 0.003 9.6e-6
Basics of Ultrasound ImagingMustafa Karaman, PhD 15
Basics of Ultrasound ImagingMustafa Karaman, PhD
scattering
16
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Reflection (Pulse-echo) & Transmission Modes
TX
Mode
(t>r/c)
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A Sample Pulse-echo Signal
s(t)
S(w)
3.5Mhz, 40%BW
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Attenuation in Pulse-Echo
ReII 2
0
F loss
(MHz) (dB/cm) (dB)
3.5 2.8 112
5.0 4.0 160
R
II 0
Medium Attenuation: Diffraction Attenuation:
Basics of Ultrasound ImagingMustafa Karaman, PhD 20
Attenuation TGC
• Attenuation: compensated by TGC amplifier
• Gain: Operator controlled at discrete
range segments
range
gain
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TGC Applied to B-Scan Image
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Pulse-Echo Ultrasonic Imaging System
Basics of Ultrasound ImagingMustafa Karaman, PhD
Transducers
23
PZT: Lead Zirconate Titanate
Basics of Ultrasound ImagingMustafa Karaman, PhD
PZT: Lead Zirconate Titanate
24
ZPZT~30x105 g/cm2s ZSKIN=~1.7x105 g/cm2s
Basics of Ultrasound ImagingMustafa Karaman, PhD
CMUT
25
vout
Vdc
~ vac
Generated Acoustic Wave
Incident Acoustic Wave
Basics of Ultrasound ImagingMustafa Karaman, PhD
Trasnsducer Bandwidth
26
Basics of Ultrasound ImagingMustafa Karaman, PhD
Trasnsducer Bandwidth
27
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Beamforming
• Perhaps the most important building block.
• Probably the most expensive building block.
– 30 - 50% of parts & labor of a scanner
• Forming transmit/receive beams
Scan image plane (reconstruct image).
This slide is from K. Thomenius’ presentation.
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Basics of Ultrasound ImagingMustafa Karaman, PhD 30
Basics of Ultrasound ImagingMustafa Karaman, PhD
Focusing
31
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steering
32
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Scan (Beam) Lines
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Beamforming = steering + focusing
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Tra
ns
du
ce
rs &
Sc
an
Fo
rma
ts
Transducer
Array
Active Subarray
Scan Line
Beam
Transducer Array = Active Subarray
Scan Line
Beam
Transducer
Array
Active
Subarray
Sc
an
Lin
e
Beam
Linear Array Curvi-Linear Array Phased Array
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Basics of Ultrasound ImagingMustafa Karaman, PhD 37
End of Session-1
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Basics of Ultrasound Imaging
Session 2
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Transducer
Array
Active Subarray
Scan Line
Beam
Transducer Array = Active Subarray
Scan Line
Beam
Transducer
Array
Active
Subarray
Sc
an
Lin
e
Beam
Linear Array Curvi-Linear Array Phased Array
Recall From Session-1:
Transducers & Scan Formats
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Recall From Session-1: Beamforming
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PSF
• Point Spread Function
– Image of a point reflector (target)
• Also called LSF (line spread function)
– 2D cross-sectional image of line reflector (target)
• Represents the spatial impulse response of the (linear) imaging system.
• Used to characterize
– transducer response (radiation pattern, beam pattern)
– the image quality of the system.
Basics of Ultrasound ImagingMustafa Karaman, PhD 42
r
(r,)
D/2x
dx
Observation
point
Geometry for driving PSF
-D/2
Excitation Pulse: p(t)
Aperture
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PSF
( / )
Signal at the observation point:
( / )( , ) cos
Assume paraxial case: cos 1 &
1( , ) ( / )
For CW excitation: ( )
( , )
D
D
jwt
wj
jw t c jwt c
D D
p t cs t dx
r
s t p t r c dxr
p t e
s t e dx e e dx
Basics of Ultrasound ImagingMustafa Karaman, PhD 44
PSF
2
( , )( , ) /
wj
jwt jwtcjwt
D
wjc
D
j
D
s th w e e dx e
e
e dx
e dx
Temporal frequency response
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Near & Far Fields
2 2
2
2
2
2 sin
21 sin
[1 ( ) ( ) ...]
r x rx
x xr
r r
r O x O x
2
2
[1 ( ) ( )] Near-Field (Fresnel)
/ Far-Field (Fraunhofer)
[1 ( )]
sin
r O x O x
r D
r O x
r x
Distance from source point to observation point:
r
(r,)
x
dxAperture
Basics of Ultrasound ImagingMustafa Karaman, PhD 46
One-Way PSF
2
22 / sin
2 / sin
( , )
(sin , )
(sin ) ( )
{ ( )}
sin / sin
/ sin
j
D
j r j x
D
j x
D
D
h w e dx
h w e e dx
h a x e dx
F a x
D
(r,)
dx
Aperture
Function
aD(x)
Basics of Ultrasound ImagingMustafa Karaman, PhD 47
(sin ) (sin )t rh h
One-Way (Tx & Rx) PSF
• Transmit and receive responses of an
aperture are identical.
• Transmit and receive beam patterns (PSFs)
of a transducer are identical.
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3dB width
main lobe
side lobes
1/ 2
PSF for D=16sin(8 sin )
(sin )0.5 sin
h
Sin
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Aperture & Sampled Aperture (Array)
d
(r,
r
1 2 3 N
Continious
Aperture
Function
Sampled
Aperture
Function
d
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PSF of Sampled Aperture (Array)
1
sin( sin )2
(sin ) exp( sin )
sin( sin )
N
n
Ndh j nd
d
• Note that: It is a periodic sinc()-like function with
a period of sin=2/d.
– Sampling in one FT domain corresponds to periodicity
in the other FT domain.
• This results in repeated main lobes, so called
grating lobes.
• To avoid grating lobes, choose d/2
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Array PSF with Grating Lobes
main lobe 3dB beam width
first side lobe
side lobes
Grating lobe grating lobe
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Two-Way PSF
2
(sin ) (sin ) (sin )
sin( sin )(sin ) (sin )
sin( sin )
sin( sin )(sin )
sin( sin )
t r
t r
TR
h h h
Ndh h
d
Ndh
d
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sin 0.5 16 sin(sin )
sin 0.5 sinh
One-Way PSF
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Two-Way PSF
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Two-Way Pulsed PSFs
R: 1D 2D 3D 4D 5D 6D 7D
arr
ay (
N=
16
, d
=/2
)
-0.5
0.0
+0.5
Basics of Ultrasound ImagingMustafa Karaman, PhD 56
Mesh Plot of Two-Way PSFs
1D
2D
3D
4D
5D
6D
7D
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Effective Aperture
)(sin)(sin
)}()({
)}({)(sin
)()()(
rt
rt
e
rte
hh
xaxaF
xaFh
xaxaxa
Basics of Ultrasound ImagingMustafa Karaman, PhD 58
Aperture Apodization
Array Channels
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Apodized PSF
)(sin)(sin
]}[][{)(sin
hW
nanwFha
Basics of Ultrasound ImagingMustafa Karaman, PhD 60
Effect of Apodization on PSF
Xtr & Rcv Hamming Window
Xtr & Rcv Uniform Window
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Depth of Focal Zone
focal point
depth of focal zone
2
2
88 nofD
rr
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F/number Apodization
RangeD 2D
f/number = Rfocal / Deffective, Deffective= D * cos
• Used for improved focal zone.
Basics of Ultrasound ImagingMustafa Karaman, PhD
f/number apodization
63
Basics of Ultrasound ImagingMustafa Karaman, PhD 64
Effective Aperture Size
r
(r,)
D
steering angle
focal point
D cos
effective aperture
Basics of Ultrasound ImagingMustafa Karaman, PhD 65
Aperture Apodization
• increases depth of focal zone
•suppresses side lobes
• reduces point resolution
(increases main lobe width)
• reduces T/R power (SNR)
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Pulse-Echo Ultrasound Imaging System
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Output Signal of Beamformer
(Beamformed A-scan)
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Beamformer Output
rN
n
nn crttptAts1
)/)(()()(
t rN
k
N
n
knnk crtttptAtAts1 1
)/2)()(()()()(
Receive Beamforming:
T/R Beamforming (synthetic):
Basics of Ultrasound ImagingMustafa Karaman, PhD 69
Wavefronts With/out Focusing
Row-1: No focusing, Row-2: Xtr focusing, Row-3: Xtr & Rcv focusing
(N=64)
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End of Session-2
Basics of Ultrasound ImagingMustafa Karaman, PhD 71
Basics of Ultrasound Imaging
Session 3
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Sector Scan
Basics of Ultrasound ImagingMustafa Karaman, PhD 73
Scan-Conversion
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Scan-Conversion
/)(
/)(
/)(
121
1212
1211
CCCC
rdBBBC
rdAAAC
Basics of Ultrasound ImagingMustafa Karaman, PhD 75
Scan-Conversion
sin
Ran
ge (r)
x
y
Basics of Ultrasound ImagingMustafa Karaman, PhD 76
Logarithmic Compression
• To view regions with different contrast levels on the same display range
a = 10db_floor/20; % a=0.01 for db_floor=-40;
x = x / xmax;
if x()<a then x() = a
y = 20 log10(x)
• 40 dB < dB_floor < 60 dB
Basics of Ultrasound ImagingMustafa Karaman, PhD 77
Image Resolution
• Axial (range) resolution
• Lateral (azimuth) resolution
• Point resolution
•Contrast resolution
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Aixal & Lateral Resolution
R: 1D 2D 3D 4D 5D 6D 7D
arr
ay (
N=
16
, d
=/2
)
-0.5
0.0
+0.5
Basics of Ultrasound ImagingMustafa Karaman, PhD 79
Resolution of B-Scan Image
axia
llateral
Basics of Ultrasound ImagingMustafa Karaman, PhD 80
Axial & Lateral Resolution
• Axial (Range) Resolution
pulse shape
pulse width
Xducer bandwith
• Lateral (Azimuth) Resolution
array size
frequency & BW
apodization
Basics of Ultrasound ImagingMustafa Karaman, PhD 81
Point Resolution
• capability of resolving point targets
main lobe width
3 dB resolution: FWHP of main lobe
6 dB resolution: FWHM of main lobe
nofD
rFWHM 22.122.1
Basics of Ultrasound ImagingMustafa Karaman, PhD 82
Contrast Resolution
• capability of resolving regions with different
contrast levels
ratio of power in main lobe to power
in side lobes
Contrast-to-Nose-Ratio:2
2
2
1
21
CNR
Basics of Ultrasound ImagingMustafa Karaman, PhD 83
Delay & Amplitude Quantization
• Delay & Amplitude Quantization side lobe level contrast resolution
• RMS Array/Delay Quantization Errors/ Main Lobe Amplitude
» m=fs/fo=32, N=128 - 59 dB
• RMS Signal-amplitude Quantization Sidelobe Level / Max Image
Amplitude
» N=128, B=8 bits -74 dB
(Peterson & Kino IEEE Trans. UFF, July 1984)
Nmd
6
NBa32
1
Basics of Ultrasound ImagingMustafa Karaman, PhD 84
Real-Time Imaging Constraint
sfiring
cxRangex
frame
firingsx
s
frames1
/2
192
1/1540/20.0220
frame
firings
sfiring
smmxx
frame
firingsx
s
frames
Basics of Ultrasound ImagingMustafa Karaman, PhD 85
Beam Space Sampling
maxmaxmax sin
/2
sin2
sin
sin2
e
e
NN
B
NBNNNNN ert
22
2/145sinsin 0
max
179128 BN
Basics of Ultrasound ImagingMustafa Karaman, PhD 86
Issues
• volumetric scan hardware
• digital systems ADC cost
• flow imaging correlation proces.
• phase aberration resolution
• motion artifacts resolution
Basics of Ultrasound ImagingMustafa Karaman, PhD 87
Dimension of a Transducer Array
This slide is from K. Thomenius’ presentation.
Basics of Ultrasound ImagingMustafa Karaman, PhD 88
3-D Imaging using 2-D Arrays
Basics of Ultrasound ImagingMustafa Karaman, PhD 89
Why 2D?
This slide is from K. Thomenius’ presentation.
Basics of Ultrasound ImagingMustafa Karaman, PhD 90
Volumetric Imaging
# of array channels (NxN) Hardware
32x32 = 1K, 64x64 = 4K, 128x128 = 16K
• 2D sparse arrays with 256 channels currently
available for 3D/4D imaging.
• For ergonomic scanning, the number of cables should be limited by 256 – 512.
# of Beam lines Frame rate
New scanning methods needed.
Basics of Ultrasound ImagingMustafa Karaman, PhD 91
Doppler Frequency
cos2 0fc
vff d
v: flow velocity (?)
f = fd: average Doppler frequency
c: ultrasound velocity
fo: ultrasound frequency
: angle between beam and velocity
Basics of Ultrasound ImagingMustafa Karaman, PhD 92
Correlation Processing
• Differential phase/delay
• Phase of complex correlation coeff.
• Index of max of RF correlation func.
Estimation of motion, phase aberration, flow
k nnk nn
k
nn
nn
ksksksks
ksks
*
11
*
*
1
1,
)()()()(
)()(
k nnk nn
k nn
nn
mksmksksks
mksksm
)()()()(
)()()(
11
1
1,
Basics of Ultrasound ImagingMustafa Karaman, PhD 93
RF Correlation
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Non-Aberrated Wavefronts
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Phase Aberration
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Phase Aberration
Row-1: No aberration., Row-2: 1x aberration., Row-3: 2x aberration
(N=64)
Basics of Ultrasound ImagingMustafa Karaman, PhD 97
Motion!
Maximum Velocity of Heart
Heart Valve cm/s =0.44mm 20 frames/s
– normal 30 cm/s 680 /s 34 /frame
– higher 60 cm/s 1360 /s 68 /frame
– abnormal 100 cm/s 2270 /s 134 /frame
Heart Wall 1-15 cm/s 20-340 /s 1-17 /frame
Basics of Ultrasound ImagingMustafa Karaman, PhD 98
End of Session-3