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Principle of Ultrasound Imaging

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Principle of Ultrasound Imaging

  1. 1. Cheaper, Faster, Better: Rapid Advances in Medical Ultrasound Kevin J. Parker, Ph.D. Professor and Dean School of Engineering and Applied Sciences University of Rochester
  2. 2. Cheaper, Faster, Better: Rapid Advances in Medical Ultrasound Presented at the Whitaker Foundation Biomedical Engineering Research Conference August, 2001 La Jolla, California
  3. 3. Outline: 1) A Brief Introduction 2) Cheaper, Faster, Better: The Revolution 3) From Physics to Bedside I: The Nonlinear Revolution 4) From Physics to Bedside II: The Promise of Elasticity Imaging 5) From Genes to Bedside: Emerging Therapeutics and Diagnostics
  4. 4. A Brief Introduction to Ultrasound • Ultrasound is a widely-used medical imaging modality • Means of interrogation: – High-frequency sound is transmitted into the body, usually in very short pulses – Returning echoes are analyzed to create an image
  5. 5. Ultrasound • Ultrasound – Sound whose frequency is greater than that perceivable by humans (>20kHz) • Medical Ultrasound – Imaging • 1-12MHz (>40MHz in specialized applications) • 1.5 mm ≤ λ ≤ 0.125 mm – Therapy: • 100kHz-1MHz • Heating, cauterization, cavitation
  6. 6. Principle of Ultrasound Imaging • Launch short (0.2-2 µs) ultrasound pulse into tissue • Listen for sound reflected and scattered by tissues – Reflections due to variations in acoustic impedance • Display gray-scale image – x - transducer location – y - time-of-flight – brightness - echo strength
  7. 7. Generation & Detection of US • Transducer – Converts one form of energy to another • Piezoelectric materials – Convert electrical signals into mechanical motion – Convert strain into electrical signals • Electric impulse creates ultrasound pulse • Ultrasound converted to electrical signal
  8. 8. US Capabilities & Limitations + Provides Real-Time imaging + Color Doppler → Non-invasive flow measurement + Essentially non-toxic + Inexpensive – Poor or no imaging through bone, gas – Operator dependant image quality – Images more difficult to interpret than CT
  9. 9. Ultrasound Images CAROTID ARTERY KIDNEY HEART
  10. 10. Cheaper, Faster, Better: The Revolution
  11. 11. Moore’s Law • The observation made in 1965 by Gordon Moore, co- founder of Intel, that the number of transistors per square inch on integrated circuits had doubled every year since the integrated circuit was invented. Moore predicted that this trend would continue for the foreseeable future. In subsequent years, the pace slowed down a bit, but data density has doubled approximately every 18 months, and this is the current definition of Moore's Law, which Moore himself has blessed. Most experts, including Moore himself, expect Moore's Law to hold for at least another two decades.
  12. 12. Terason™ 2000 The unique Terason™ 2000 with its high performance SmartProbe™ links directly to a PC, making diagnostic ultrasound an intuitive PC application. Now clinicians can realize big-system performance anywhere with this ultraportable, plug-and-play system.
  13. 13. Features • Unique, proprietary system-on-a-chip technology • Plug-and-play PC options - faster exams, perfect for QuickLook™ decisions • Ultimate portability - patient access in virtually any setting • Superb image quality via high-channel-count and bandwidth • Broad choice of Terason SmartProbes optimized for specific applications • Storage, import and export thousands of images • Network-and telemedicine-ready
  14. 14. Kidney Detail
  15. 15. Internal Carotid Stenosis
  16. 16. Color SieScape® Imaging enables panoramic visualization of flow in this normal kidney, renal artery and vein.
  17. 17. Greater sapheneous vein Color SieScape Panoramic Image.
  18. 18. 3D Ultrasound • Various applications are under investigation – Obstetric, guided biopsy, cardiac Copyright © 2000 Kretztecknik AG. All rights reserved.
  19. 19. © 2000 ATL Ultrasound. All rights reserved.
  20. 20. From Physics to Bedside I: The Nonlinear Revolution
  21. 21. Connection Between the Fay and Fubini Solutions for Plane Sound Waves of Finite Amplitude David T. Blackstock Acoustical Physics Laboratory, Electrical Engineering Department University of Rochester, Rochester, NY 14627 Plane, progressive, periodic sound waves of finite amplitude are considered. The well-known solutions of Fay and Fabini are reviewed. At first glance, the two solutions seem contradictory, but, actually, each holds in a different region of the flow, the Fubini solution close to the source and the Fay solution rather far from the source. In the intermediate, or transition, region, neither solution is valid. A more general solution is obtained by using a method commonly employed for waves containing weak shocks. For distances up to the shock-formation point, the general solution reduces exactly to the Fubini solution. For distances greater than about 3.5 shock-formation lengths, the general solution is practically indistinguishable from the sawtooth solution, which, in turn, is the limiting form of Fay’s solution for strong waves. The form of the general solution shows clearly how, in the transition region, the Fubini solution gives way to the sawtooth solution. The problem of an isolated cycle of an originally sinusoidal wave is also considered. Finally, some limitations on the weak-shock method are discussed. In the periodic-wave problem, the general solution is found to be inaccurate for distances greater than 1/α, approximately, where α is the small-signal absorption coefficient. Journal of the Acoustical Society of America Volume 3, Number 6, 1966 In 1966, David Blackstock launched a theory of nonlinear wave propagation, now known as “weak shock theory” from his work at the University of Rochester. It would be over 30 years until the benefits for imaging were widely known. Today, in 2001, every high end ultrasound scanner has nonlinear imaging.
  22. 22. Shock amplitude of an originally sinusoidal wave. Inset shows the waveform at various distances from the source.
  23. 23. Amplitudes of the fundamental, second-harmonic, and third-harmonic components in an originally sinusoidal wave.
  24. 24. Harmonic beam patterns at a range of 117 yard for a source level of 109dB and frequency 454 kHz.
  25. 25. Ultrasound in Med. & Biol., Vol 6, pp. 359-368 Pergamon Press Ltd., 1980. Printed in Great Britain DEMONSTRATION OF NONLINEAR ACOUSTICAL EFFECTS AT BIOMEDICAL FREQUENCIES AND INTENSITIES Abstract — Examples of nonlinear acoustic phenomena in water in the range of frequencies and intensities of interest for biomedical ultrasound are provided. Total intensities, including all harmonics generated in the medium have been measured with a spherical radiometer. The fundamental component of the waves have been measured with a miniature probe hydrophone and low pass filter Simple adaptation of the theory summarized in a companion paper leads to predictions which are in excellent agreement with the observations. The illustrated phenomena must be considered in studies of the biological effects of ultrasound as well as in the applications of ultrasound in medicine. E. L. Carstensen, W. K. Law and N. D. McKay Department of Electrical Engineering, The University of Rochester, Rochester, NY 14627, U.S.A. T. G. Muir Applied Research Laboratories, The University of Texas at Austin, Austin, TX 78712, U.S.A. (First Received 20 July 1979; and in final form 20 February 1980) IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 44, NO. 1, JANUARY 1997 Finite Amplitude Distortion-Based Inhomogeneous Pulse Echo Ultrasonic Imaging Ted Christopher Abstract — Ultrasonic pulse echo imaging in inhomogeneous media suffers from significant lateral and contrast resolution losses due to the de- focusing effects of the inhomogeneities. The losses in lateral and contrast resolution are associated with increases in the width of the main-beam and increases in sidelobe levels, respectively. These two forms of resolution loss represent significant hurdles to improving the clinical utility of biomedical ultrasonic imaging. A number of research efforts are currently underway to investigate the defocusing effects of tissue and to consider corrective measures. All of these efforts assume linear propagation, and base the image-formation process on the reception of the transmitted pulse. A novel pulse echo imaging scheme in which the image is formed using the finite amplitude distortion components of the received pulse is considered here. Alternatively, this could be described as image formation using the nonlinearly-generated higher harmonics. Early Work in Nonlinear Imaging
  26. 26. 128XP Fundamental Image 128XP Native Tissue Harmonic Imaging Linear Image Nonlinear Image (Notice sharper contrast and definition of Boundaries.
  27. 27. From Physics to Bedside II: The Promise of Elasticity Imaging
  28. 28. Scope • Sonoelastography: the visualization of hard tumors in soft tissue using their relative elastic properties • 3D Sonoelastography: A 3D image created by assembling a spatial sequence of 2D images • Results of a phantom tumor study and ex-vivo prostate study are presented
  29. 29. CIRS Prostate Phantom
  30. 30. 2D B-scan and Sonoelastography Image of the Same Region in the Prostate Phantom Isoechoic tumor
  31. 31. Prostate Experiments Excised prostates were obtained from patients diagnosed with prostate cancer and scanned using similar procedures Vibration frequencies in the range 150-300 Hz were used to get color fill in the variance images Results of ultrasound scans were compared to those determined by pathology
  32. 32. 3D rendering of MR and ultrasound data from the prostate phantom. The MR segmentation of the gland is shown as a surface rendering in transparent gray to serve as a geometrical reference for the tumor. The MR segmentation of the tumor is shown in blue, the segmented tumor from the sonoelastography image is orange. The urethra is visible as a transparent tube running from the apex to the base of the gland.
  33. 33. From Genes to Bedside: Emerging Therapeutics and Diagnostics
  34. 34. Energy Mediated Drug Delivery Targeting Ligand Encapsulated Drug Gas • Microbubbles with ligands to bind to selected targets • Potential targets: – platelets and/or fibrin for thrombosis – integrins and selectins for endothelial cells (e.g., in angiogenesis and vascular disease) – Other targets for cancer, inflammation and infection • Combination of diagnostic and therapeutic agents for activation with ultrasound
  35. 35. Localized Release of Therapeutics From Price, et al., Circulation, 1998;98:1264-1267
  36. 36. FluoroGene™ • Effective vehicle for gene delivery to the skin, lungs and other tissue 0 200 400 600 800 1000 * = Significant Effect ng/ml CAT protein Cells LF LF w/FGF2 FG FG w/FGF2 * *
  37. 37. Gene Delivery to Mouse Tumors CAT (ng/g Tissue) 0.001 0.01 0.1 1 10 15 45 90 C ontrol Tumor S onoPorated Cationic Liposomes (continuous wave, non-focused ultrasound, f = 1.0 MHz) DNA (ng)
  38. 38. What I Haven’t Covered: • 3D Revolution • Fusion with MRI • Contrast Agents • Transmit Pulse Encodings • Doppler Advances • Quantitative Estimations of Microstructure • High Frequency Microscopy • Numerous Specialized Developments
  39. 39. Cheaper, Faster, Better: The Revolution
  40. 40. Acknowledgements • Dr. Anne Hall General Electric Medical Systems • Dr. Evan Unger ImaRx Therapeutics, Inc. • Dr. Deborah Rubens Rochester Center for Biomedical Ultrasound