1. 1 Resolution Enhancement Compression- Synthetic Aperture Focusing Student: Hans Bethe Advisor: Dr. Jose R. Sanchez Bradley University Department of Electrical Engineering

2. 2 Motivation Ultrasound Imaging is important in medical diagnosis Figure 1: Imaging fetus [1]Figure 2: Imaging fetus [1]

3. 3 Motivation Ultrasound imaging involves exciting transducer and forming ultrasound beams Ultrasound imaging involves exciting transducer and forming ultrasound beams Synthetic Aperture Focusing (SAF): a beam-forming technique which can improve lateral resolution 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 Resolution Enhancement Compression (REC): coded excitation technique for exciting transducer which can increase echo-signal-to-noise-ratio (eSNR) => increase axial resolution Objectives: Objectives: a/ Investigate REC and SAFT techniques through literature research and simulation b/ Combine REC and SAFT

4. 4 Outline I. Ultrasound Imaging System II. Synthetic Aperture Focusing (SAF) III. Resolution Enhancement Compression (REC)

5. 5 I. Ultrasound Imaging System Transducer Image construction system Figure 3: Example of an imaging system [2]

6. 6 Transducer Converts signal or energy of one form to another Converts 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 echoes Emits ultrasound pulses and and receives echoes Target Ultrasound pulses Echoes Transducer Figure 4: Ultrasound emission and reflection

7. 7 Image Construction System Pre- amplifier Matched filter Echo A Delay Unit Transducer excitation A Apodization RAM image ADDER

8. 8 Image Construction System Pre- amplifier Matched filter Echo A Delay Unit Transducer excitation A Apodization RAM image ADDER

9. 9 Image Construction System Pre- amplifier Matched filter Echo A Delay Unit Transducer excitation A Apodization RAM image ADDER Minimize effect of noise by suppressing noise outside input frequency band => increases signal-to-noise ratio (SNR) of output

10. 10 Image Construction System Pre- amplifier Matched filter Echo A Delay Unit Transducer excitation A Apodization RAM image ADDER

11. 11 Image Construction System Pre- amplifier Matched filter Echo A Delay Unit Transducer excitation A Apodization RAM image ADDER

12. 12 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 Control beam width => improve or degrade lateral resolution Figure 5: Illustration of apodization Center

13. 13 Beam 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

14. 14 Image Construction System Pre- amplifier Matched filter Echo A Delay Unit Transducer excitation A Apodization RAM image ADDER

15. 15 Image Construction System Pre- amplifier Matched filter Echo A Delay Unit Transducer excitation A Apodization RAM image ADDER

16. 16 II. Synthetic Aperture Focusing (SAF)

17. 17 In synthetic aperture focusing (SAF), a single transducer element is used both, in transmit and receive modes 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 Each element in the transducer emits pulses one by one 1 2 3 target Echo Pulse Figure 7: Illustration of SAF

18. 18 SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer Target L1L1 L3L3 L6L6 L9L9 pulses Figure 8: Illustration of DAS

19. 19 SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer Target L1L1 L3L3 L6L6 L9L9 pulses Figure 8: Illustration of DAS echoes

20. 20 SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer Target L1L1 L3L3 L6L6 L9L9 pulses Figure 8: Illustration of DAS echoes

21. 21 SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer Target L1L1 L3L3 L6L6 L9L9 Figure 8: Illustration of DAS Transducer Delay unit pulses echoes

22. 22 SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer Target L1L1 L3L3 L6L6 L9L9 Figure 8: Illustration of DAS Transducer Delay unit Sum pulses echoes

23. 23 III. Resolution Enhancement Compression (REC)

24. 24 WHY REC? Figure 9: Resolution Comparison [3]Figure 10: Background-target separation [3] Before REC, conventional pulsing (CP) was used Before REC, conventional pulsing (CP) was used CP proved ineffective in term of image resolution CP proved ineffective in term of image resolution

25. 25 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 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: 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

26. 26 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 chirp 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 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 Figure 11: Illustration of axial resolution beam axis

27. 27 Figure 12: Effect pulse duration has on axial resolution echoes objects

28. 28 Figure 10: Illustration of convolution equivalence principle

29. 29 REC Mechanism

30. 30 REC Mechanism

31. 31 REC Mechanism

32. 32 REC Mechanism

33. 33

34. 34 Functional Requirements I/ SAF Transducer shall consist of a linear array of elements Transducer 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.

35. 35 Functional Requirements II/ REC The impulse response of the imaging system (denoted as h1(t)) shall have a center frequency f0 of 2 MHz. 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%. 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 bandwidth about 1.5 times the bandwidth of h1(t). 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 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.

36. 36 Schedule

37. 37 Patents 1/ Ultrasound signal compression Inventors: A. W. Wegener (Aptos Hill, CA, US), M. V. Nanevics (Palo Alto, CA, US) Inventors: A. W. Wegener (Aptos Hill, CA, US), M. V. Nanevics (Palo Alto, CA, US) Assignees: Samplify Systems, Inc. Assignees: Samplify Systems, Inc. IPC8 Class: AA61B806FI IPC8 Class: AA61B806FI USPC Class: 600454 USPC Class: 600454 Class name: Ultrasonic doppler effect blood flow studies Class name: Ultrasonic doppler effect blood flow studies Patent application number: 20120157852 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 Inventors: Richard Yung Chiao, Ann Lindsay Hall, Kai Erik ThomeniusRichard Yung ChiaoAnn Lindsay HallKai Erik ThomeniusRichard Yung ChiaoAnn Lindsay HallKai Erik Thomenius Original Assignee: General Electric Company Original Assignee: General Electric CompanyGeneral Electric CompanyGeneral Electric Company Current U.S. Classification: 600/447; 600/458 Current U.S. Classification: 600/447; 600/458600/447600/458600/447600/458 International Classification: A61B 800 International Classification: A61B 800

38. 38 Patents 3/ Ultrasonic imaging system with beamforming using unipolar or bipolar coded excitation Inventors: Richard Yung Chiao, Lewis Jones Thomas, III Inventors: Richard Yung Chiao, Lewis Jones Thomas, IIIRichard Yung ChiaoLewis Jones Thomas, IIIRichard Yung ChiaoLewis Jones Thomas, III Original Assignee: General Electric Company Original Assignee: General Electric CompanyGeneral Electric CompanyGeneral Electric Company Primary Examiner: Ali M. Imam Primary Examiner: Ali M. Imam Current U.S. Classification: 600/447 Current U.S. Classification: 600/447600/447 International Classification: A61B 800 International Classification: A61B 800 4/ Synthetic aperture ultrasound imaging system Inventors: J. Robert Fort, Norman S. Neidell, Douglas J. Morgan, Phillip C. Landmeier Inventors: J. Robert Fort, Norman S. Neidell, Douglas J. Morgan, Phillip C. LandmeierJ. Robert FortNorman S. NeidellDouglas J. MorganPhillip C. LandmeierJ. Robert FortNorman S. NeidellDouglas J. MorganPhillip C. Landmeier Current U.S. Classification: 600/447; 73/597; 600/437 Current U.S. Classification: 600/447; 73/597; 600/437 International Classification: A61B 800 International Classification: A61B 800

39. 39 Patents 5/ System and method for adaptive beamformer apodization Inventor: Hong Wang Inventor: Hong WangHong WangHong Wang Original Assignee: Siemens Medical Solutions USA, Inc. Original Assignee: Siemens Medical Solutions USA, Inc.Siemens Medical Solutions USA, Inc.Siemens Medical Solutions USA, Inc. Primary Examiner: Marvin M. Lateef Primary Examiner: Marvin M. Lateef Secondary Examiner: Ali M. Imam Secondary Examiner: Ali M. Imam Current U.S. Classification: 600/443 Current U.S. Classification: 600/443600/443 International Classification: A61B/800 International Classification: A61B/800 6/ Transducer array imaging system Inventors: Kevin S. Randall, Jodi Schwartz Klessel, Anthony P. Lannutti, Joseph A. Urbano Inventors: Kevin S. Randall, Jodi Schwartz Klessel, Anthony P. Lannutti, Joseph A. UrbanoKevin S. RandallJodi Schwartz KlesselAnthony P. LannuttiJoseph A. UrbanoKevin S. RandallJodi Schwartz KlesselAnthony P. LannuttiJoseph A. Urbano Original Assignee: Penrith Corporation Original Assignee: Penrith CorporationPenrith CorporationPenrith Corporation Primary Examiner: Jacques M Saint Surin Primary Examiner: Jacques M Saint Surin Attorney: Condo Roccia LLP Attorney: Condo Roccia LLP Current U.S. Classification: 73/661; 73/620; 73/649; 600/443; 600/447 Current U.S. Classification: 73/661; 73/620; 73/649; 600/443; 600/44773/66173/62073/649600/443600/44773/66173/62073/649600/443600/447

40. 40 References [1] Ultrasound images gallery http://www.ultrasound-images.com/pancreas.htmhttp://www.ultrasound-images.com/pancreas.htm [2] http://sell.bizrice.com/selling-leads/48391/Digital-Portable-Color-Doppler-Ultrasound- System.htmlhttp://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 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] [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.

41. 41 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’