Transcript REC-SAFT - Bradley

Resolution Enhancement CompressionSynthetic Aperture Focusing Techniques
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 pancreas [1]
2
Motivation

Ultrasound imaging involves exciting transducer and forming ultrasound
pulses to be fired at internal tissue

Synthetic Aperture Focusing Techniques (SAFT): beam-forming techniques
capable of enhancing lateral resolution

Resolution Enhancement Compression (REC): coded excitation (wave
shaping) technique employed to produce excitation signal capable of
enhancing 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. Functional Requirements
III. Progress
4
I. Ultrasound Imaging System
Excitation
(REC)
Image
reconstruction
system
Transducer
Beam-forming
(SAFT)
Figure 3: Block diagram
5
Transducer

Converts signal or energy of one form to another
 In imaging, converts electrical signal to ultrasound signal
Transducer
Target
Ultrasound pulses
Echoes
Figure 4: Ultrasound emission and reflection
6
Image Reconstruction System
excitation
Transducer
A
Echo
Preamplifier
Apodization
Matched
filter
Σ
Delay
Unit
A
image
7
Image Reconstruction System
excitation
Transducer
A
Echo
Preamplifier
Apodization
Matched
filter
Σ
Delay
Unit
A
image
8
Image Reconstruction System
excitation
Transducer
A
Echo
Preamplifier
Apodization
Matched
filter
Σ
Delay
Unit
A
image
9
Image Reconstruction System
excitation
Transducer
A
Echo
Preamplifier
Apodization
Matched
filter
Σ
Delay
Unit
A
image
10
Image Reconstruction System
excitation
Transducer
A
Echo
Preamplifier
Apodization
Matched
filter
Σ
Delay
Unit
A
image
11
Image Reconstruction System
excitation
Transducer
A
Echo
Preamplifier
Apodization
Matched
filter
Σ
Delay
Unit
A
image
12
III. Functional Requirements
A/ SAFT

Transducer shall be a linear array comprising 128 elements
 SAFT shall be performed through MATLAB Field II
 SAFT mode: excite all elements and receive with 1 element person emission
 Delay and sum calculations shall be performed through a GPGPU
 Total synthetic aperture processing time shall be < 1 second
(Adjustment: total processing time shall be about 10-20 seconds)
 Signal-to-noise ratio (SNR) of the images shall be at least 50 dB
13
III. Functional Requirements
B/ REC





Actual impulse response of system (denoted as h1(t)) shall have a center
frequency f0 of 2 MHz.
System bandwidth shall be about 83%.
Sampling frequency fs shall be 400 MHz.
Desired impulse response of imaging system (denoted as h2(t) ) shall have a
bandwidth about 1.5 times the bandwidth of h1(t).
The side lobes associated with compressed pulse shall be reduced below 40 dB.
14
Sep 2012
ID
Oct 2012
Nov 2012
Dec 2012
Jan 2013
Feb 2013
Mar 2013
Apr 2013
May 2013
Task Name
% Complete
9/2 9/9 9/16 9/23 9/30 10/7 10/14 10/21 10/28 11/4 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 Literature research for REC and SAFT
100%
2 Generating impulse responses h1(t). h2(t)
100%
Generating pre-enhanced chirp excitation
signal
100%
3
4 Pulse Compression
100%
5 Hilbert Transform and log compression
100%
6 Beam forming through Field I
20%
7 Simulation through GPGPU
0%
8 Write final report
0%
9 Student expo
0%
10 Final presentation
0%
11 Create website for project
100%
12 Update project website
100%
15
Sep 2012
ID
Oct 2012
Nov 2012
Dec 2012
Jan 2013
Feb 2013
Mar 2013
Apr 2013
May 2013
Task Name
% Complete
9/2 9/9 9/16 9/23 9/30 10/7 10/14 10/21 10/28 11/4 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 Literature research for REC and SAFT
100%
2 Generating impulse responses h1(t). h2(t)
100%
Generating pre-enhanced chirp excitation
signal
100%
3
4 Pulse Compression
100%
5 Hilbert Transform and log compression
100%
6 Beam forming through Field I
20%
7 Simulation through GPGPU
0%
8 Write final report
0%
9 Final presentation
0%
10 Create website for project
100%
11 Update project website
16
100%
Actual impulse h1 (t)
Pre-enhanced chirp
1
1
0.5
0.5
0
0
0
-0.5
-1
0
1
V
0.5
V
V
1
-0.5
0.5
1
t(s)
1.5
x 10
-0.5
-1
0
2
h1 (t)*Vpre -chirp(t)
1
-6
Desired impulse h2 (t)
t(s)
-1
0
2
x 10
1
-5
Linear chirp
1
1
t(s)
2
x 10
-5
x 10
-5
h2 (t)*Vlin-chirp(t)
0.8
0.6
0.5
0.5
0.4
V
0
V
V
0.2
0
0
-0.2
-0.4
-0.5
-0.5
-0.6
-0.8
-1
0
0.5
1
t(s)
1.5
2
x 10
-6
-1
0
0.5
1
t(s)
1.5
2
-1
0
1
-5
x 10
t(s)
2
Figure 5: Illustration of convolution equivalence principle
h1 (t ) * v pre chirp (t )  h2 (t ) * vlinchirp (t )
17
REC Mechanism
Actual impulse h1(t)
0.5
0.5
0
0
-0.5
-1
0
Pre-enhanced chirp
1
V
V
1
-0.5
0.5
1
t(s)
1.5
-1
0
2
x 10
0.5
1
-6
Desired impulse h2(t)
1
t(s)
1.5
2
2.5
x 10
-5
Linear chirp
1
0.8
0.6
0.5
0.4
0
V
V
0.2
0
-0.2
-0.4
-0.5
-0.6
-0.8
-1
0
0.5
1
t(s)
1.5
2
x 10
-6
-1
0
0.2
0.4
0.6
0.8
1
t(s)
1.2
1.4
1.6
1.8
2
-5
x 10
18
REC Mechanism
Actual impulse h1(t)
0.5
0.5
0
0
-0.5
-1
0
Pre-enhanced chirp
1
V
V
1
-0.5
0.5
1
t(s)
1.5
-1
0
2
x 10
0.5
1
-6
Desired impulse h2(t)
1
t(s)
1.5
2
2.5
x 10
-5
Linear chirp
1
0.8
0.6
0.5
0.4
0
V
V
0.2
0
-0.2
-0.4
-0.5
-0.6
-0.8
-1
0
0.5
1
t(s)
1.5
2
x 10
-6
-1
0
0.2
0.4
0.6
0.8
1
t(s)
1.2
1.4
1.6
1.8
2
-5
x 10
19
REC Mechanism
Actual impulse h1(t)
0.5
0.5
0
0
-0.5
-1
0
Pre-enhanced chirp
1
V
V
1
-0.5
0.5
1
t(s)
1.5
-1
0
2
x 10
0.5
1
-6
Desired impulse h2(t)
1
t(s)
1.5
2
2.5
x 10
-5
Linear chirp
1
0.8
0.6
0.5
0.4
0
V
V
0.2
0
-0.2
-0.4
-0.5
-0.6
-0.8
-1
0
0.5
1
t(s)
1.5
2
x 10
-6
-1
0
0.2
0.4
0.6
0.8
1
t(s)
1.2
1.4
1.6
1.8
2
-5
x 10
20
REC Mechanism
Actual impulse h1(t)
0.5
0.5
0
0
-0.5
-1
0
Pre-enhanced chirp
1
V
V
1
-0.5
0.5
1
t(s)
1.5
-1
0
2
x 10
0.5
1
-6
Desired impulse h2(t)
1
t(s)
1.5
2
2.5
x 10
-5
Linear chirp
1
0.8
0.6
0.5
0.4
0
V
V
0.2
0
-0.2
-0.4
-0.5
-0.6
-0.8
-1
0
0.5
1
t(s)
1.5
2
x 10
-6
-1
0
0.2
0.4
0.6
0.8
1
t(s)
1.2
1.4
1.6
1.8
2
-5
x 10
21
Actual impulse h1 (t)
Pre-enhanced chirp
1
1
0.5
0.5
0
0
0
-0.5
-1
0
1
V
0.5
V
V
1
-0.5
0.5
1
t(s)
1.5
x 10
-0.5
-1
0
2
h1 (t)*Vpre -chirp(t)
1
-6
Desired impulse h2 (t)
t(s)
-1
0
2
x 10
1
-5
Linear chirp
1
1
t(s)
2
x 10
-5
x 10
-5
h2 (t)*Vlin-chirp(t)
0.8
0.6
0.5
0.5
0.4
V
0
V
V
0.2
0
0
-0.2
-0.4
-0.5
-0.5
-0.6
-0.8
-1
0
0.5
1
t(s)
1.5
2
x 10
-6
-1
0
0.5
1
t(s)
1.5
2
-1
0
1
-5
x 10
t(s)
2
Figure 15: Illustration of convolution equivalence principle
22
1
0.9
res
0.8
0.7
REC
CP
1 2

2 k0
MTF
0.6
0.5
0.4
K0(REC)
0.3
K0(CP)
0.2
0.1
0
0
0.5
1
1.5
2
2.5
k (m-1)
3
3.5
4
Figure 16: Axial resolution between CP and REC
4.5
5
x 10
4
23
QUESTIONS ?
24
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.
25
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’
26
Apodization
1. Process of varying signal strengths
in transmission and reception across
transducer
2. Reduces side lobes
3. Signal strength will become
progressively weaker with
increasing distance from the center
Center
4. Control beam width => improve or
degrade lateral resolution
Figure 5: Illustration of apodization
27
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
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
28
II. Theoretical Background
29
SAFT
• In synthetic aperture focusing techniques (SAFT), 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
30
The essence of SAFT is delay-and-sum (DAS) operation
Transducer
L1
L3
L6
L9
pulses
Target
Figure 8: Illustration of DAS
31
The essence of SAFT is delay-and-sum (DAS) operation
Transducer
L1
L3
L6
L9
echoes
pulses
Target
Figure 8: Illustration of DAS
32
The essence of SAFT is delay-and-sum (DAS) operation
2 L1
t1 
c
2 L3
t3 
c
Transducer
L1
L3
L6
L9
2 L6
t6 
c
2 L9
t9 
c
echoes
pulses
Target
Figure 8: Illustration of DAS
33
The essence of SAFT is delay-and-sum (DAS) operation
2 L1
t1 
c
Delay
unit
2 L3
t3 
c
Transducer
L1
L3
L6
L9
2 L6
t6 
c
2 L9
t9 
c
echoes
pulses
Target
Figure 8: Illustration of DAS
34
The essence of SAFT is delay-and-sum (DAS) operation
Delay
unit
Sum
2 L1
t1 
c
2 L3
t3 
c
Transducer
L1
L3
L6
L9
2 L6
t6 
c
2 L9
t9 
c
echoes
pulses
Target
Figure 8: Illustration of DAS
35
Figure 9: Illustration of delay-and-sum [4]
36
REC


Before REC, conventional pulsing (CP) was used
CP proved ineffective in term of image resolution
Figure 10: Resolution Comparison [3]
Figure 11: Background-target separation [3]
37
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
38

REC: a coded excitation technique (wave shaping)
 Employs Convolution Equivalence Principle to generate pre-enhanced chirp
excitation signal
 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 12: Illustration of axial resolution
39
echoes
objects
Figure 13: Effect pulse duration has on axial resolution
40
h1 (t)
1
1
0.5
0.5
0
0
0
-0.5
-1
0
V
0.5
V
V
1
Vpre -chirp(t)
-0.5
0.5
1
t(s)
1.5
x 10
1
-6
h1 (t)
1
-0.5
-1
0
2
t(s)
-1
0
2
x 10
1
-5
 (t)
1
t(s)
2
x 10
-5
x 10
-6
h1 (t)*  (t)
1
0.8
0.5
h1 (t)*Vpre -chirp(t)
0.5
V
0
V
V
0.6
0
0.4
-0.5
-1
0
-0.5
0.2
0.5
1
t(s)
1.5
2
x 10
-6
0
0
0.5
1
t(s)
1.5
2
x 10
-1
0
-6
Figure 16: Comparison between CP and REC
0.5
1
t(s)
1.5
41
2