11

Resolution Enhancement Compression-Resolution Enhancement Compression-Synthetic Aperture FocusingSynthetic Aperture Focusing

Student:Student:

Hans BetheHans Bethe

Advisor: Dr. Jose R. SanchezAdvisor: Dr. Jose R. Sanchez

Bradley UniversityBradley University

Department of Electrical EngineeringDepartment of Electrical Engineering

22

MotivationMotivationUltrasound Imaging is important in medical diagnosisUltrasound Imaging is important in medical diagnosis

Figure 1: Imaging fetus [1] Figure 2: Imaging fetus [1]

33

MotivationMotivation Ultrasound imaging involves exciting transducer and forming ultrasound Ultrasound imaging involves exciting transducer and forming ultrasound

beamsbeams

Synthetic Aperture Focusing (SAF): a beam-forming technique which can Synthetic Aperture Focusing (SAF): a beam-forming technique which can improve lateral resolutionimprove lateral resolution

Resolution Enhancement Compression (REC): coded excitation technique Resolution Enhancement Compression (REC): coded excitation technique for exciting transducer which can increase echo-signal-to-noise-ratio for exciting transducer which can increase echo-signal-to-noise-ratio (eSNR) => increase axial resolution (eSNR) => increase axial resolution

Objectives: Objectives: a/ Investigate REC and SAFT techniques through literature research and a/ Investigate REC and SAFT techniques through literature research and

simulationsimulationb/ Combine REC and SAFTb/ Combine REC and SAFT

44

OutlineOutline

I. Ultrasound Imaging SystemI. Ultrasound Imaging System

II. Synthetic Aperture Focusing (SAF)II. Synthetic Aperture Focusing (SAF)

III. Resolution Enhancement Compression III. Resolution Enhancement Compression (REC)(REC)

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I. Ultrasound Imaging SystemI. Ultrasound Imaging System

Transducer

Image construction

system

Figure 3: Example of an imaging system [2]

66

TransducerTransducer Converts signal or energy of one form to anotherConverts signal or energy of one form to another In imaging, converts electrical signal to ultrasound signal In imaging, converts electrical signal to ultrasound signal Emits ultrasound pulses and and receives echoesEmits ultrasound pulses and and receives echoes

Target

Ultrasound pulses

Echoes

Transducer

Figure 4: Ultrasound emission and reflection

77

Image Construction SystemImage Construction System

Pre-amplifier

MatchedfilterEcho ADelay

UnitTransducer

excitation

A Apodization RAMimage

ADDER

88

Image Construction SystemImage Construction System

Pre-amplifier

MatchedfilterEcho ADelay

UnitTransducer

excitation

A Apodization RAMimage

ADDER

99

Image Construction SystemImage Construction System

Pre-amplifier

MatchedfilterEcho ADelay

UnitTransducer

excitation

A Apodization RAMimage

ADDER

Minimize effect of noise by suppressing noise outside input frequency band => increases signal-to-noise ratio (SNR) of output

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Image Construction SystemImage Construction System

Pre-amplifier

MatchedfilterEcho ADelay

UnitTransducer

excitation

A Apodization RAMimage

ADDER

1111

Image Construction SystemImage Construction System

Pre-amplifier

MatchedfilterEcho ADelay

UnitTransducer

excitation

A Apodization RAMimage

ADDER

1212

ApodizationApodization

• 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

• Control beam width => improve or degrade lateral resolution

Figure 5: Illustration of apodization

Center

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Beam width and lateral resolutionBeam width and lateral resolution

Figure 6: Illustration of the effect beam width has on lateral resolution

1 2 3

• 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 ultrasound pulses covering objects => echoes from reflectors more likely to merge => degrade lateral resolution

objects

transducer

beam

beam axis

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Image Construction SystemImage Construction System

Pre-amplifier

MatchedfilterEcho ADelay

UnitTransducer

excitation

A Apodization RAMimage

ADDER

1515

Image Construction SystemImage Construction System

Pre-amplifier

MatchedfilterEcho ADelay

UnitTransducer

excitation

A Apodization RAMimage

ADDER

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II. Synthetic Aperture Focusing II. Synthetic Aperture Focusing (SAF)(SAF)

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• In synthetic aperture focusing (SAF), a single transducer element is used both, in transmit In synthetic aperture focusing (SAF), a single transducer element is used both, in transmit and receive modesand receive modes• Each element in the transducer emits pulses one by oneEach element in the transducer emits pulses one by one

1 2 3

target

Echo

Pulse

Figure 7: Illustration of SAF

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SAFT implementations are performed using a delay-and-sum (DAS) processing in time SAFT implementations are performed using a delay-and-sum (DAS) processing in time domaindomain

Transducer

Target

L1

L3L6

L9

pulses

Figure 8: Illustration of DAS

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SAFT implementations are performed using a delay-and-sum (DAS) processing in time SAFT implementations are performed using a delay-and-sum (DAS) processing in time domaindomain

Transducer

Target

L1

L3L6

L9

pulses

Figure 8: Illustration of DAS

echoes

2020

SAFT implementations are performed using a delay-and-sum (DAS) processing in time SAFT implementations are performed using a delay-and-sum (DAS) processing in time domaindomain

Transducer

Target

L1

L3L6

L9

pulses

Figure 8: Illustration of DAS

c

Lt 3

3

2

c

Lt 6

6

2

c

Lt 9

9

2

c

Lt 11

2

echoes

2121

SAFT implementations are performed using a delay-and-sum (DAS) processing in time SAFT implementations are performed using a delay-and-sum (DAS) processing in time domaindomain

Transducer

Target

L1

L3L6

L9

Figure 8: Illustration of DAS

Transducer

Delay unit

c

Lt 3

3

2

c

Lt 6

6

2

c

Lt 9

9

2

c

Lt 11

2

pulses

echoes

2222

SAFT implementations are performed using a delay-and-sum (DAS) processing in time SAFT implementations are performed using a delay-and-sum (DAS) processing in time domaindomain

Transducer

Target

L1

L3L6

L9

Figure 8: Illustration of DAS

Transducer

Delay unit

Sum

c

Lt 3

3

2

c

Lt 6

6

2

c

Lt 9

9

2

c

Lt 11

2

pulses

echoes

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III. Resolution Enhancement III. Resolution Enhancement Compression (REC)Compression (REC)

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WHY REC?WHY REC?

Figure 9: Resolution Comparison [3] Figure 10: Background-target separation [3]

Before REC, conventional pulsing (CP) was usedBefore REC, conventional pulsing (CP) was used CP proved ineffective in term of image resolutionCP proved ineffective in term of image resolution

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WHY REC?WHY REC? To enhance image resolution by CP, increase excitation voltage => produces To enhance image resolution by CP, increase excitation voltage => produces

excessive heating => hazardous to patients => a better excitation technique is excessive heating => hazardous to patients => a better excitation technique is needed => gave rise to the investigation of RECneeded => gave rise to the investigation of REC

Advantages of REC:Advantages of REC:a/ Improves axial resolution without increasing acoustic peak powera/ Improves axial resolution without increasing acoustic peak powerb/ Offers the capability to obtain the optimal FM chirp to increase the bandwidth of b/ Offers the capability to obtain the optimal FM chirp to increase the bandwidth of

imaging systemimaging system

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REC: a coded excitation technique (coded excitation = FM or PM waveform)REC: a coded excitation technique (coded excitation = FM or PM waveform) Employs Convolution Equivalence Principle to generate pre-enhanced chirpEmploys Convolution Equivalence Principle to generate pre-enhanced chirp Excitation by pre-enhanced chirp increases bandwidth of imaging system => Excitation by pre-enhanced chirp increases bandwidth of imaging system =>

produce shorter-duration pulses => increases axial resolutionproduce shorter-duration pulses => increases axial resolution

(axial resolution = ability of imaging system to distinguish objects closely spaced along(axial resolution = ability of imaging system to distinguish objects closely spaced along

the axis of the beam)the axis of the beam)

objects

transducer

beam

Figure 11: Illustration of axial resolution

beam axis

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Figure 12: Effect pulse duration has on axial resolution

echoes objects

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0 0.5 1 1.5 2

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(t)*h2(t)

t (s)

V

Figure 10: Illustration of convolution equivalence principle

)(*)()(*)( 21 tvthtvth chirplinchirppre

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x 10-6

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-0.5

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h1(t) (actual transducer impulse response)

t (s)

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nit

ud

e (V

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x 10-6

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REC MechanismREC Mechanism

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x 10-6

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t (s)

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x 10-6

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(t)

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nit

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x 10-6

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t (s)

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REC MechanismREC Mechanism

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x 10-6

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REC MechanismREC Mechanism

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x 10-6

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REC MechanismREC Mechanism

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Functional RequirementsFunctional RequirementsI/ SAFI/ SAF Transducer shall consist of a linear array of elementsTransducer shall consist of a linear array of elements SAF shall be performed through MATLAB Field II. SAF shall be performed through MATLAB Field II. Total memory consumption shall not > 2 gigabytes.Total memory consumption shall not > 2 gigabytes. Delay and sum calculations shall be performed through a GPGPU.Delay and sum calculations shall be performed through a GPGPU. Total synthetic aperture processing time shall be < 1 second.Total synthetic aperture processing time shall be < 1 second. Signal-to-noise ratio (SNR) of the images shall be at least 50 dB.Signal-to-noise ratio (SNR) of the images shall be at least 50 dB.

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Functional RequirementsFunctional RequirementsII/ RECII/ REC The impulse response of the imaging system (denoted as h1(t)) shall have a The impulse response of the imaging system (denoted as h1(t)) shall have a

center frequency f0 of 2 MHz. center frequency f0 of 2 MHz. h1(t) shall have a bandwidth of about 83%. h1(t) shall have a bandwidth of about 83%. The sampling frequency fs shall be 400 MHz.The sampling frequency fs shall be 400 MHz. The desired impulse response of imaging system (denoted as h2(t) ) shall have a The desired impulse response of imaging system (denoted as h2(t) ) shall have a

bandwidth about 1.5 times the bandwidth of h1(t). 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 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.The side lobes of shall be reduced below 40 dB.

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ID Task NameNov 2012

11/11 11/18

1 Pulse Compression through MATLAB

3 Beam forming through Field II

4 Simulation through GPGPU

5 Write final report

Final presentation

Dec 2012

11/25 12/2 12/9

Jan 2013 Feb 2013 Mar 2013

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

2 Hilbert Transform and log compression

Apr 2013

3/24 3/31 4/7 4/14 4/21 4/28

May 2013

5/5

7 Update project website

6

ScheduleSchedule

3737

PatentsPatents1/ Ultrasound signal compression1/ Ultrasound signal compression Inventors:  A. W . Wegener (Aptos Hill, CA, US), M. V. Nanevics (Palo Alto, Inventors:  A. W . Wegener (Aptos Hill, CA, US), M. V. Nanevics (Palo Alto,

CA, US) CA, US) Assignees:  Samplify Systems, Inc. Assignees:  Samplify Systems, Inc. IPC8 Class: AA61B806FIIPC8 Class: AA61B806FI USPC Class: 600454USPC Class: 600454 Class name: Ultrasonic doppler effect blood flow studiesClass name: Ultrasonic doppler effect blood flow studies Patent application number: 20120157852 Patent application number: 20120157852

2/ 2/ Ultrasound imaging using coded excitation on transmit and selective filtering of Ultrasound imaging using coded excitation on transmit and selective filtering of fundamental and sub-harmonic signals on receivefundamental and sub-harmonic signals on receive

Inventors: Inventors: Richard Yung Richard Yung ChiaoChiao, , Ann Lindsay HallAnn Lindsay Hall, , Kai Erik Kai Erik ThomeniusThomenius Original Assignee: Original Assignee: General Electric CompanyGeneral Electric Company Current U.S. Classification: Current U.S. Classification: 600/447600/447; ; 600/458600/458 International Classification: A61B 800 International Classification: A61B 800

3838

PatentsPatents3/ Ultrasonic imaging system with beamforming using unipolar or bipolar coded 3/ Ultrasonic imaging system with beamforming using unipolar or bipolar coded

excitationexcitation Inventors: Inventors: Richard Yung Richard Yung ChiaoChiao, , Lewis Jones Thomas, IIILewis Jones Thomas, III Original Assignee: Original Assignee: General Electric CompanyGeneral Electric Company Primary Examiner: Ali M. ImamPrimary Examiner: Ali M. Imam Current U.S. Classification: Current U.S. Classification: 600/447600/447 International Classification: A61B 800 International Classification: A61B 800

4/ 4/ Synthetic aperture ultrasound imaging systemSynthetic aperture ultrasound imaging system Inventors: J. Robert Fort, Norman S. Neidell, Douglas J. Morgan, Phillip C. Inventors: J. Robert Fort, Norman S. Neidell, Douglas J. Morgan, Phillip C.

LandmeierLandmeier Current U.S. Classification: 600/447; 73/597; 600/437Current U.S. Classification: 600/447; 73/597; 600/437 International Classification: A61B 800International Classification: A61B 800

3939

PatentsPatents5/ System and method for adaptive beamformer apodization5/ System and method for adaptive beamformer apodization Inventor: Inventor: Hong WangHong Wang Original Assignee: Original Assignee: Siemens Medical Solutions USA, Inc.Siemens Medical Solutions USA, Inc. Primary Examiner: Marvin M. LateefPrimary Examiner: Marvin M. Lateef Secondary Examiner: Ali M. ImamSecondary Examiner: Ali M. Imam Current U.S. Classification: Current U.S. Classification: 600/443600/443 International Classification: A61B/800International Classification: A61B/800

6/ 6/ Transducer array imaging systemTransducer array imaging system Inventors: Inventors: Kevin S. RandallKevin S. Randall, , Jodi Schwartz Jodi Schwartz KlesselKlessel, , Anthony P. Anthony P. LannuttiLannutti, ,

Joseph A. Joseph A. UrbanoUrbano Original Assignee: Original Assignee: PenrithPenrith Corporation Corporation Primary Examiner: Jacques M Saint SurinPrimary Examiner: Jacques M Saint Surin Attorney: Condo Roccia LLPAttorney: Condo Roccia LLP Current U.S. Classification: Current U.S. Classification: 73/66173/661; ; 73/62073/620; ; 73/64973/649; 600/443; 600/447 ; 600/443; 600/447

4040

ReferencesReferences[1] Ultrasound images gallery http://www.ultrasound-images.com/pancreas.htm

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

[3] J. R. Sanchez et al., "A Novel Coded Excitation Scheme to Improve Spatial and Contrast [3] J. R. Sanchez et al., "A Novel Coded Excitation Scheme to Improve Spatial and Contrast Resolution of Quantitative Ultrasound Imaging" Resolution of Quantitative Ultrasound Imaging" IEEE Trans Ultrasonics, Ferroelectrics, and IEEE Trans Ultrasonics, Ferroelectrics, and Frequency Control,Frequency Control, vol. 56, no. 10, pp. 2111-2123, October 2009. vol. 56, no. 10, pp. 2111-2123, October 2009.

[4] S. I. Nikolov, “Synthetic Aperture Tissue and Flow Ultrasound Imaging[4] S. I. Nikolov, “Synthetic Aperture Tissue and Flow Ultrasound Imaging

[5] [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.

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ReferencesReferences[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 [9] Tadeusz Stepinski, “An Implementation of Synthetic Aperture Focusing Technique in Frequency Domain”,Frequency Domain”, IEEE transactions on Ultrasonics, Ferroelectrics, and Frequency IEEE transactions on Ultrasonics, Ferroelectrics, and Frequency control, control, vol. 54, no. 7, July 2007vol. 54, no. 7, July 2007

[10] J. A. Zagzebski, “Essentials of Ultrasound Physics’[10] J. A. Zagzebski, “Essentials of Ultrasound Physics’