Resolution Enhancement Compression- Synthetic Aperture Focusing

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

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

3. 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

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

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

6. 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

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

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

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

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

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

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 Center Figure 5: Illustration of apodization

13. 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 ultrasound pulses covering objects => echoes from reflectors more likely to merge => degrade lateral resolution beam axis transducer beam objects 1 2 3 Figure 6: Illustration of the effect beam width has on lateral resolution

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

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

16. II. Synthetic Aperture Focusing (SAF)

17. 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

18. SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer L6 L3 L1 L9 pulses Target Figure 8: Illustration of DAS

19. SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer L6 L3 L1 L9 echoes pulses Target Figure 8: Illustration of DAS

20. SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Transducer L6 L3 L1 L9 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 Transducer Transducer L6 L3 L1 L9 echoes pulses Target Figure 8: Illustration of DAS

22. SAFT implementations are performed using a delay-and-sum (DAS) processing in time domain Delay unit Sum Transducer Transducer L6 L3 L1 L9 echoes pulses Target Figure 8: Illustration of DAS

23. III. Resolution Enhancement Compression (REC)

24. 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]

25. 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 WHY REC?

26. 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

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

28. Figure 10: Illustration of convolution equivalence principle

29. REC Mechanism

30. REC Mechanism

31. REC Mechanism

32. REC Mechanism

34. 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. Functional Requirements

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. • 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.

36. Schedule

37. 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

38. 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

39. 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

40. References [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 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.

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’