resolution enhancement compression synthetic aperture focusing techniques n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Resolution Enhancement Compression- Synthetic Aperture Focusing Techniques PowerPoint Presentation
Download Presentation
Resolution Enhancement Compression- Synthetic Aperture Focusing Techniques

Loading in 2 Seconds...

play fullscreen
1 / 50

Resolution Enhancement Compression- Synthetic Aperture Focusing Techniques - PowerPoint PPT Presentation


  • 98 Views
  • Uploaded on

Resolution Enhancement Compression- Synthetic Aperture Focusing Techniques. Student: Hans Bethe Advisor: Dr. Jose R. Sanchez Bradley University Department of Electrical Engineering. Motivation. Ultrasonic imaging (UI) is important in medical diagnosis.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Resolution Enhancement Compression- Synthetic Aperture Focusing Techniques' - pamela-green


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
resolution enhancement compression synthetic aperture focusing techniques

Resolution Enhancement Compression-Synthetic Aperture Focusing Techniques

Student:

Hans Bethe

Advisor: Dr. Jose R. Sanchez

Bradley University

Department of Electrical Engineering

motivation
Motivation

Ultrasonic imaging (UI) is important in medical diagnosis

Figure 1: Ultrasound image of kidney stone [1]

Figure 2: Ultrasound image of pancreas [2]

motivation1
Motivation

1. One of the main concerns in UI: improving spatial resolution of ultrasonic images

2. Resolution Enhancement Compression (REC): a coded excitation (or wave-shaping) technique. Its functions:

Produces a pre-enhanced chirp capable of improving axial resolution

Improves SNR through compression

3. Synthetic Aperture Focusing Techniques (SAFT): a set of beam-forming techniques, capable of improving lateral resolution and SNR by delay processing

4. Objectives:

Investigate and simulate REC and SAFT independently

Combine REC and SAFT to determine the improvement in both lateral and axial directions as well as SNR

outline
Outline

I. Ultrasonic imaging system

II. REC

III. SAFT

IV. Functional requirements

V. Simulation results

i ultrasonic imaging system
I. Ultrasonic Imaging System

REC

(excitation)

SAFT

(delay

processing)

REC

(compression)

Image

reconstruction

system

Transducer

Figure 3: Block diagram

transducer
Transducer

An electro-mechanical device used to convert signal or energy of one form to another

In imaging, converts electrical signal to ultrasonic signal

Transducer

Target

Ultrasonic pulses

Echoes

Figure 4: Ultrasound emission and reflection

image reconstruction system
Image Reconstruction System

excitation

Pre-

amplifier

Matched

filter

Delay

Unit

A

Transducer

Echo

image

A

Apodization

Σ

image reconstruction system1
Image Reconstruction System

excitation

Pre-

amplifier

Matched

filter

Delay

Unit

A

Transducer

Echo

image

A

Apodization

Σ

image reconstruction system2
Image Reconstruction System

excitation

Pre-

amplifier

Matched

filter

Delay

Unit

A

Transducer

Echo

image

A

Apodization

Σ

image reconstruction system3
Image Reconstruction System

excitation

Pre-

amplifier

Matched

filter

Delay

Unit

A

Transducer

Echo

image

A

Apodization

Σ

image reconstruction system4
Image Reconstruction System

excitation

Pre-

amplifier

Matched

filter

Delay

Unit

A

Transducer

Echo

image

A

Apodization

Σ

image reconstruction system5
Image Reconstruction System

excitation

Pre-

amplifier

Matched

filter

Delay

Unit

A

Transducer

Echo

image

A

Apodization

Σ

ii rec
REC: a coded excitation and pulse compression technique

Coded excitation amounts to wave-shaping

Coded excitation involves generating the pre-enhanced chirp excitation signal, capable of artificially increasing a transducer’s bandwidth => yields higher axial resolution

(axial resolution = ability of imaging system to distinguish objects closely spaced along the axis of the beam)

II. REC

objects

transducer

beam axis

beam

Figure 5: Illustration of axial resolution

rec mechanism
REC Mechanism

Figure 6: Coded excitation illustration

rec mechanism1
REC Mechanism

Figure 6: Coded excitation illustration

rec mechanism2
REC Mechanism

Figure 6: Coded excitation illustration

rec mechanism3
REC Mechanism

Figure 6: Coded excitation illustration

slide19
The 2nd central aspect of REC is pulse-echo compression, accomplished by a Wiener compression filter
  • γ : varies the operating point of β(f) between inverse filter and matched filter states
  • V’lin-chirp(f): frequency spectrum of modified linear chirp.
slide20
The 2nd central aspect of REC is pulse-echo compression, accomplished by a Wiener compression filter
  • γ : varies the operating point of β(f) between inverse filter and matched filter states
  • V’lin-chirp(f): frequency spectrum of modified linear chirp.

The original linear chirp cannot be used in β(f) because the pre-enhanced chirp is tapered by Hanning window => convolution equivalence principle no longer holds.If original linear chirp is used, β(f) will yield considerable side lobes => need modified linear chirp

slide21
SAFT = synthetic aperture focusing techniques = different beam-forming techniques

Different techniques exist:

Generic synthetic aperture (GSA)

Synthetic transmit aperture (STA)

Synthetic receive aperture (SRA)

Synthetic transmit and receive aperture (STRA)

III. SAFT

slide22
SAFT = synthetic aperture focusing techniques = different beam-forming techniques

Different techniques exist:

Generic synthetic aperture (GSA)

Synthetic transmit aperture (STA)

Synthetic receive aperture (SRA)

Synthetic transmit and receive aperture (STRA)

III. SAFT

slide23

STA

emission 1

emission 2

emission 3

emission 4

reception 1

reception 2

reception 3

reception 4

LRI 1

LRI 2

LRI 3

LRI 4

Σ

Figure 7: Illustration of STA

slide24

The essence of STA is delay-and-sum (DAS) operation

Transducer

L6

L3

L1

L9

pulses

Target

Figure 8: Illustration of DAS

slide25

The essence of SAFT is delay-and-sum (DAS) operation

Transducer

L6

L3

L1

L9

echoes

pulses

Target

Figure 8: Illustration of DAS

slide26

The essence of SAFT is delay-and-sum (DAS) operation

Transducer

L6

L3

L1

L9

echoes

pulses

Target

Figure 8: Illustration of DAS

slide27

The essence of SAFT is delay-and-sum (DAS) operation

Delay processing

Transducer

Transducer

L6

L3

L1

L9

echoes

pulses

Target

Figure 8: Illustration of DAS

slide28

The essence of SAFT is delay-and-sum (DAS) (or focusing in reception) processing

Delay processing

Σ

Transducer

Transducer

L6

L3

L1

L9

echoes

pulses

Target

Figure 8: Illustration of DAS

iv functional requirements
A/ STA

Transducer shall be a linear array comprising 128 elements

STA shall be performed through MATLAB Field II

STA mode: synthetic transmit aperture (STA)

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

IV. Functional Requirements
iii functional requirements
III. Functional Requirements

B/ REC

  • Actual impulse response h1(t) of transducer shall have a frequency of 2 MHz.
  • Transducer bandwidth shall be about 83%.
  • Sampling rate shall be 400 MHz.
  • Impulse response h2(t) of desired transducer 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.
slide37
Quality metrics used to assess REC

1/ Signal-to-noise ratio (SNR)

- SNR of conventional pulsing (CP): 38.49 dB

- SNR of REC: 47.83 dB

=> SNR is improved when REC is utillized

2/ Modulation transfer function: used to determine the axial resolution of the system

slide40
Quality metrics used to assess STA

1/ Signal-to-noise ratio (SNR)

- SNR before delay processing: 36.89 dB

- SNR after delay processing: 50.44 dB

=> SNR is improved after delay processing is implemented

2/ Modulation transfer function: used to determine the axial resolution of the system

slide43

Pre-delay k0 = 407.3 m-1

Post-delay k0 = 454.1 m-1

Axial improvement factor = 1.11

Figure 15: Axial resolution simulation result

references
References

[1] Ultrasound image gallery http://www.ultrasound-images.com/renal-calculi.htm

[2] Ultrasound images gallery http://www.ultrasound-images.com/pancreas.htm

[3] http://sell.bizrice.com/selling-leads/48391/Digital-Portable-Color-Doppler-Ultrasound-System.html

[4] 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.

[5] S. I. Nikolov, “Synthetic Aperture Tissue and Flow Ultrasound Imaging

[6] 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.

[7] M. L. Oelze, “Bandwidth and Resolution Enhancement Through Pulse Compression”, IEEE Trans. Ultrasonics, Ferroelectrics, and Frequency Control, vol. 54, no. 4, April 2007.

references1
References

[8] 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.

[9] M. Oelze, “Improved Axial Resolution Using Pre-enhanced Chirps and Pulse Compression”, 2006 IEEE Ultrasonics Symposium

[10] 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

[11] J. A. Zagzebski, “Essentials of Ultrasound Physics’

apodization
Apodization
  • Process of varying signal strengths in transmission and reception across transducer
  • Reduces side lobes
  • Signal strength will become progressively weaker with increasing distance from the center
  • Control beam width => improve or degrade lateral resolution

Center

Figure 5: Illustration of apodization

slide49

objects

echoes

Figure 7: Effect pulse duration has on axial resolution

beam width and lateral resolution
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
  • Larger beam width => greater likelihood of pulses covering objects => echoes from reflectors more likely to merge => degrade lateral resolution

beam axis

transducer

beam

objects

1

2

3

Figure 5: Illustration of the effect beam width has on lateral resolution