Resolution Enhancement CompressionSynthetic Aperture Focusing
Student:
Hans Bethe
Advisor: Dr. Jose R. Sanchez
Bradley University
Department of Electrical Engineering
1
Motivation
Ultrasound Imaging is important in medical diagnosis
Figure 1: Imaging fetus [1]
Figure 2: Imaging fetus [1]
2
Motivation

Ultrasound imaging involves exciting transducer and forming ultrasound
beams

Synthetic Aperture Focusing (SAF): a beam-forming technique which can
improve lateral resolution

Resolution Enhancement Compression (REC): coded excitation technique
for exciting transducer which can increase echo-signal-to-noise-ratio
(eSNR) => increase axial resolution

Objectives:
a/ Investigate REC and SAFT techniques through literature research and
simulation
b/ Combine REC and SAFT
3
Outline
I. Ultrasound Imaging System
II. Synthetic Aperture Focusing (SAF)
III. Resolution Enhancement Compression
(REC)
4
I. Ultrasound Imaging System
Image
construction
system
Transducer
Figure 3: Example of an imaging system [2]
5
Transducer

Converts signal or energy of one form to another
 In imaging, converts electrical signal to ultrasound signal
 Emits ultrasound pulses and and receives echoes
Transducer
Target
Ultrasound pulses
Echoes
Figure 4: Ultrasound emission and reflection
6
Image Construction System
excitation
Transducer
Echo
Preamplifier
Matched
filter
Delay
Unit
A
image
A
Apodization
RAM
ADDER
7
Image Construction System
excitation
Transducer
Echo
Preamplifier
Matched
filter
Delay
Unit
A
image
A
Apodization
RAM
ADDER
8
Image Construction System
excitation
Transducer
Echo
Preamplifier
Matched
filter
Delay
Unit
A
image
A
Apodization
RAM
ADDER
Minimize effect of noise by suppressing noise outside input frequency band => increases
signal-to-noise ratio (SNR) of output
9
Image Construction System
excitation
Transducer
Echo
Preamplifier
Matched
filter
Delay
Unit
A
image
A
Apodization
RAM
ADDER
10
Image Construction System
excitation
Transducer
Echo
Preamplifier
Matched
filter
Delay
Unit
A
image
A
Apodization
RAM
ADDER
11
Apodization
• Process of varying signal strengths in
transmission and reception across
transducer
• Reduces side lobes
• Signal strengths decreases with
increasing distance from center =>
elements closer to center receive
stronger excitation signals
Center
• Control beam width => improve or
degrade lateral resolution
Figure 5: Illustration of apodization
12
Beam width and lateral resolution
• Lateral resolution = capability of imaging
system to distinguish 2 closely spaced objects
positioned perpendicular to the axis of
ultrasound beam
beam
axis
transducer
• Larger beam width => greater likelihood of
ultrasound pulses covering objects => echoes
from reflectors more likely to merge =>
degrade lateral resolution
beam
objects
1
2
3
Figure 6: Illustration of the effect beam
width has on lateral resolution
13
Image Construction System
excitation
Transducer
Echo
Preamplifier
Matched
filter
Delay
Unit
A
image
A
Apodization
RAM
ADDER
14
Image Construction System
excitation
Transducer
Echo
Preamplifier
Matched
filter
Delay
Unit
A
image
A
Apodization
RAM
ADDER
15
II. Synthetic Aperture Focusing
(SAF)
16
• In synthetic aperture focusing (SAF), a single transducer element is used both, in transmit
and receive modes
• Each element in the transducer emits pulses one by one
1
2
3
Pulse
Echo
target
Figure 7: Illustration of SAF
17
SAFT implementations are performed using a delay-and-sum (DAS) processing in time
domain
Transducer
L1
L3
L6
L9
pulses
Target
Figure 8: Illustration of DAS
18
SAFT implementations are performed using a delay-and-sum (DAS) processing in time
domain
Transducer
L1
L3
L6
L9
echoes
pulses
Target
Figure 8: Illustration of DAS
19
SAFT implementations are performed using a delay-and-sum (DAS) processing in time
domain
2 L1
t1 
c
Transducer
L1
L3
L6
2 L3
t3 
c
L9
t6
2 L6

c
t9
2 L9

c
echoes
pulses
Target
Figure 8: Illustration of DAS
20
SAFT implementations are performed using a delay-and-sum (DAS) processing in time
domain
2 L1
t1 
c
Delay
unit
Transducer
L1
L3
L6
2 L3
t3 
c
L9
t6
2 L6

c
t9
2 L9

c
echoes
pulses
Target
Figure 8: Illustration of DAS
21
SAFT implementations are performed using a delay-and-sum (DAS) processing in time
domain
Delay
unit
Sum
Transducer
L1
L3
L6
2 L1
t1 
c
2 L3
t3 
c
L9
t6
2 L6

c
t9
2 L9

c
echoes
pulses
Target
Figure 8: Illustration of DAS
22
III. Resolution Enhancement
Compression (REC)
23
WHY REC?


Before REC, conventional pulsing (CP) was used
CP proved ineffective in term of image resolution
Figure 9: Resolution Comparison [3]
Figure 10: Background-target separation [3]
24
WHY REC?

To enhance image resolution by CP, increase excitation voltage => produces
excessive heating => hazardous to patients => a better excitation technique is needed
=> gave rise to the investigation of REC

Advantages of REC:
a/ Improves axial resolution without increasing acoustic peak power
b/ Offers the capability to obtain the optimal FM chirp to increase the bandwidth of
imaging system
25

REC: a coded excitation technique (coded excitation = FM or PM waveform)
 Employs Convolution Equivalence Principle to generate pre-enhanced chirp
 Excitation by pre-enhanced chirp increases bandwidth of imaging system =>
produce shorter-duration pulses => increases axial resolution
(axial resolution = ability of imaging system to distinguish objects closely spaced along
the axis of the beam)
objects
transducer
beam
beam axis
Figure 11: Illustration of axial resolution
26
echoes
objects
Figure 12: Effect pulse duration has on axial resolution
27
Vpre-chirp(t)
1
0.5
0.5
0.5
0
-1
Magnitude (V)
1
-0.5
0
-0.5
0
0.5
1
t (s)
1.5
-1
2
0
-0.5
0
1
-6
x 10
h2(t)
2
t (s)
3
-1
4
0.5
0.5
0.5
0
0
-0.5
V
1
0
-0.5
0.5
1
t (s)
1.5
2
-6
x 10
-1
1
1.5
t (s)
2
2.5
3
-6
x 10
Vlin-chirp(t)*h2(t)
1
0
0.5
x 10
1
-1
0
-6
Vlin-chirp(t)
Magnitude (V)
Magnitude (V)
Vpre-chirp(t)*h1(t)
1
Magnitude (V)
Magnitude (V)
h1(t)
-0.5
0
0.5
1
t (s)
1.5
2
-1
0
0.5
1
-5
x 10
1.5
t (s)
2
2.5
3
-6
x 10
Figure 10: Illustration of convolution equivalence principle
h1 (t ) * v pre chirp (t )  h2 (t ) * vlinchirp (t )
28
REC Mechanism
1
h1(t) (actual transducer impulse response)
1
0.5
Magnitude (V)
Magnitude (V)
0.5
0
-0.5
-1
0
1
0.5
1
t (s)
1.5
-1
0
2
x 10
1
-6
h2(t) (desired transducer impulse response)
2
t (s)
3
4
x 10
-6
x 10
-5
Vlin-chirp(t)
1
0.5
Magnitude (V)
Magnitude (V)
0
-0.5
0.5
0
-0.5
-1
0
Vpre-chirp(t)
0
-0.5
0.5
1
t (s)
1.5
2
x 10
-6
-1
0
0.5
1
t (s)
1.5
2
29
REC Mechanism
1
h1(t) (actual transducer impulse response)
1
0.5
Magnitude (V)
Magnitude (V)
0.5
0
-0.5
-1
0
1
0.5
1
t (s)
1.5
-1
0
2
x 10
1
-6
h2(t) (desired transducer impulse response)
2
t (s)
3
4
x 10
-6
x 10
-5
Vlin-chirp(t)
1
0.5
Magnitude (V)
Magnitude (V)
0
-0.5
0.5
0
-0.5
-1
0
Vpre-chirp(t)
0
-0.5
0.5
1
t (s)
1.5
2
x 10
-6
-1
0
0.5
1
t (s)
1.5
2
30
REC Mechanism
1
h1(t) (actual transducer impulse response)
1
0.5
Magnitude (V)
Magnitude (V)
0.5
0
-0.5
-1
0
1
0.5
1
t (s)
1.5
-1
0
2
x 10
1
-6
h2(t) (desired transducer impulse response)
2
t (s)
3
4
x 10
-6
x 10
-5
Vlin-chirp(t)
1
0.5
Magnitude (V)
Magnitude (V)
0
-0.5
0.5
0
-0.5
-1
0
Vpre-chirp(t)
0
-0.5
0.5
1
t (s)
1.5
2
x 10
-6
-1
0
0.5
1
t (s)
1.5
2
31
REC Mechanism
1
h1(t) (actual transducer impulse response)
1
0.5
Magnitude (V)
Magnitude (V)
0.5
0
-0.5
-1
0
1
0.5
1
t (s)
1.5
-1
0
2
x 10
1
-6
h2(t) (desired transducer impulse response)
2
t (s)
3
4
x 10
-6
x 10
-5
Vlin-chirp(t)
1
0.5
Magnitude (V)
Magnitude (V)
0
-0.5
0.5
0
-0.5
-1
0
Vpre-chirp(t)
0
-0.5
0.5
1
t (s)
1.5
2
x 10
-6
-1
0
0.5
1
t (s)
1.5
2
32
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0
-0.2
-0.4
Magnitude (V)
1
0.2
0
-0.2
-0.4
0.2
0
-0.2
-0.4
-0.6
-0.6
-0.6
-0.8
-0.8
-0.8
-1
0
0.5
1
1.5
t (s)
-1
2
0
1
2
3
t (s)
-6
x 10
h2(t) (desired transducer impulse response)
-1
4
Vlin-chirp(t)
0.8
0.6
0.6
0.4
0.4
0.2
0.2
Magnitude (V)
-0.4
-0.6
-0.8
0
0.5
1
t (s)
1.5
2
-6
x 10
V
0.8
-0.2
0
-0.2
-0.4
-0.4
-0.6
-0.6
-0.8
-0.8
0
0.5
1
t (s)
2
2.5
3
-6
x 10
0
-0.2
-1
1.5
Vlin-chirp(t)*h2(t)
0.8
0
1
t (s)
1
0.2
0.5
x 10
1
0.4
0
-6
1
0.6
Magnitude (V)
Vpre-chirp(t)*h1(t)
V pre-chirp(t)
Magnitude (V)
Magnitude (V)
h1(t) (actual transducer impulse response)
1.5
2
-5
x 10
-1
0
0.5
1
1.5
t (s)
2
2.5
3
-6
33
x 10
Functional Requirements
I/ SAF






Transducer shall consist of a linear array of elements
SAF shall be performed through MATLAB Field II.
Total memory consumption shall not > 2 gigabytes.
Delay and sum calculations shall be performed through a GPGPU.
Total synthetic aperture processing time shall be < 1 second.
Signal-to-noise ratio (SNR) of the images shall be at least 50 dB.
34
Functional Requirements
II/ REC






The impulse response of the imaging system (denoted as h1(t)) shall have a
center frequency f0 of 2 MHz.
h1(t) shall have a bandwidth of about 83%.
The sampling frequency fs shall be 400 MHz.
The desired impulse response of imaging system (denoted as h2(t) ) shall have a
bandwidth about 1.5 times the bandwidth of h1(t).
The linear chirp shall have a bandwidth about 1.14 times the bandwidth of h2(t)
The side lobes of shall be reduced below 40 dB.
35
Schedule
Nov 2012
ID
Dec 2012
Jan 2013
Feb 2013
Mar 2013
Apr 2013
May 2013
Task Name
11/11 11/18 11/25 12/2 12/9 12/16 12/23 12/30 1/6 1/13 1/20 1/27 2/3 2/10 2/17 2/24 3/3 3/10 3/17 3/24 3/31 4/7 4/14 4/21 4/28 5/5
1 Pulse Compression through MATLAB
2 Hilbert Transform and log compression
3 Beam forming through Field I
4 Simulation through GPGPU
5 Write final report
6 Final presentation
7 Update project website
36
Patents
1/ Ultrasound signal compression
 Inventors: A. W . Wegener (Aptos Hill, CA, US), M. V. Nanevics (Palo Alto,
CA, US)
 Assignees: Samplify Systems, Inc.
 IPC8 Class: AA61B806FI
 USPC Class: 600454
 Class name: Ultrasonic doppler effect blood flow studies
 Patent application number: 20120157852
2/ Ultrasound imaging using coded excitation on transmit and selective filtering of




fundamental and sub-harmonic signals on receive
Inventors: Richard Yung Chiao, Ann Lindsay Hall, Kai Erik Thomenius
Original Assignee: General Electric Company
Current U.S. Classification: 600/447; 600/458
International Classification: A61B 800
37
Patents
3/ Ultrasonic imaging system with beamforming using unipolar or bipolar coded
excitation
 Inventors: Richard Yung Chiao, Lewis Jones Thomas, III
 Original Assignee: General Electric Company
 Primary Examiner: Ali M. Imam
 Current U.S. Classification: 600/447
 International Classification: A61B 800
4/ Synthetic aperture ultrasound imaging system

Inventors: J. Robert Fort, Norman S. Neidell, Douglas J. Morgan, Phillip C.
Landmeier
 Current U.S. Classification: 600/447; 73/597; 600/437
 International Classification: A61B 800
38
Patents
5/ System and method for adaptive beamformer apodization
 Inventor: Hong Wang
 Original Assignee: Siemens Medical Solutions USA, Inc.
 Primary Examiner: Marvin M. Lateef
 Secondary Examiner: Ali M. Imam
 Current U.S. Classification: 600/443
 International Classification: A61B/800
6/ Transducer array imaging system





Inventors: Kevin S. Randall, Jodi Schwartz Klessel, Anthony P. Lannutti, Joseph
A. Urbano
Original Assignee: Penrith Corporation
Primary Examiner: Jacques M Saint Surin
Attorney: Condo Roccia LLP
Current U.S. Classification: 73/661; 73/620; 73/649; 600/443; 600/447
39
References
[1] Ultrasound images gallery http://www.ultrasound-images.com/pancreas.htm
[2] http://sell.bizrice.com/selling-leads/48391/Digital-Portable-Color-Doppler-UltrasoundSystem.html
[3] J. R. Sanchez et al., "A Novel Coded Excitation Scheme to Improve Spatial and Contrast
Resolution of Quantitative Ultrasound Imaging" IEEE Trans Ultrasonics, Ferroelectrics, and
Frequency Control, vol. 56, no. 10, pp. 2111-2123, October 2009.
[4] S. I. Nikolov, “Synthetic Aperture Tissue and Flow Ultrasound Imaging
[5] T. Misaridis and J. A. Jensen, “Use of Modulated Excitation Signals in Medical
Ultrasound” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 52, no. 2, February 2005.
[6] M. L. Oelze, “Bandwidth and Resolution Enhancement Through Pulse Compression”,
IEEE Trans. Ultrasonics, Ferroelectrics, and Frequency Control, vol. 54, no. 4, April 2007.
40
References
[7] J. R. Sanchez and M. L. Oelze, “An Ultrasonic Imaging Speckle-Suppression and
Contrast-Enhancement Technique by Means of Frequency Compounding and Coded
Excitation”, IEEE Trans. Ultrasonics, Ferroelectrics, and Frequency Control, vol. 56, no. 7,
Julyl 2009.
[8] M. Oelze, “Improved Axial Resolution Using Pre-enhanced Chirps and Pulse
Compression”, 2006 IEEE Ultrasonics Symposium
[9] Tadeusz Stepinski, “An Implementation of Synthetic Aperture Focusing Technique in
Frequency Domain”, IEEE transactions on Ultrasonics, Ferroelectrics, and Frequency
control, vol. 54, no. 7, July 2007
[10] J. A. Zagzebski, “Essentials of Ultrasound Physics’
41