生醫工程實驗 期中報告 Ultrasound

1. 生醫工程實驗 期中報告Ultrasound Apr. 2’ 2007 第一組： 郭昱昇 溫仁揚 溫昌懌 National Taiwan University Electrical Engineering Dept.

2. Outline • History • Principles • Characteristic • Applications National Taiwan University Electrical Engineering Dept. - 2 -

3. History • publication of The Theory of Sound (Lord Rayleigh, 1877) • discovery of piezo-electric effect (Pierre Curie, 1880) • enabled generation and detection of ultrasonic waves • • first practical use in World War One for detecting submarines • • followed by • non-destructive testing of metals (airplane wings, bridges) • seismology • • first clinical use for locating brain tumors (Karl Dussik, Friederich Dussik, 1942) • • the first greyscale images were produced in 1950 • in real time by Siemens device in 1965 • • electronic beam-steering using phased-array technology in 1968 • • popular technique since mid-70s • • substantial enhancements since mid-1990 National Taiwan University Electrical Engineering Dept. - 3 -

4. Principle – Transducer • Piezoelectric National Taiwan University Electrical Engineering Dept. - 4 -

5. Principle – Focusing • Lateral Resolution = D = depth, W = wavelength, A = Aperture • F number, F# = Ex: f=5Mhz, A = 2cm, V = 1500 m/s In depth 4 cm, resolution = National Taiwan University Electrical Engineering Dept. - 5 -

6. Principle – Focusing (cont’d) • Improve • larger aperture • higher frequency (shorter wavelength) • multiple focusing • dynamic focusing National Taiwan University Electrical Engineering Dept. - 6 -

7. Principle – Focusing (cont’d) • Improve • larger aperture • higher frequency (shorter wavelength) • multiple focusing • dynamic focusing National Taiwan University Electrical Engineering Dept. - 7 -

8. Principle – Focusing (cont’d) • Improve • larger aperture • higher frequency (shorter wavelength) • multiple focusing • dynamic focusing National Taiwan University Electrical Engineering Dept. - 8 -

9. Principle – Effects : • Attenuation • The loss of energy in tissue: • f : frequency, z: depth , a0 :attenuation coefficient of medium , typically n=1 • Non-linearity • Assuming p was only a tiny disturbance of static pressure • With increasing acoustic pressure , the wave changes shape National Taiwan University Electrical Engineering Dept. - 9 -

10. Principle – Speckle • Coherent Imaging system • Interference of scatterers National Taiwan University Electrical Engineering Dept. - 10 -

11. Principle – Speckle • Scatter size (radius a) • Wavelength (λ) • Wave number K=2π/λ • Optical : ka>>1 • Rayleigh : ka<<1 • Oscillatory : between National Taiwan University Electrical Engineering Dept. - 11 -

12. Principle – Speckle Rayleigh : ka<<1 National Taiwan University Electrical Engineering Dept. - 12 -

13. Principle – Speckle • Soft tissue : less than 100μm • Independent of scattering structures • Dependent of imaging system、distance National Taiwan University Electrical Engineering Dept. - 13 -

14. Principle – Speckle • Let A be signal received from scatterer with phase θi , we have: • If N→∞ , Re{ A } and Im{ A } are asymptotically Gaussian. • Joint probability density function: National Taiwan University Electrical Engineering Dept. - 14 -

15. Principle – Speckle • Intensity I≡ Re{ A }2 +Im{ A } 2 • So for I≧0: • And amplitude E≡ is Rayleigh distribution: National Taiwan University Electrical Engineering Dept. - 15 -

16. Principle – Speckle • Define: I0 is an arbitrary reference signal • Expand f: Ignoring R , we have This noise limits the detect ability of low contrast lesions National Taiwan University Electrical Engineering Dept. - 16 -

17. Characteristic • Modes • A mode • B mode • M mode • Color Doppler mode • Acoustic impedance National Taiwan University Electrical Engineering Dept. - 17 -

18. Characteristic – Modes • A mode • B mode • M mode • CPD National Taiwan University Electrical Engineering Dept. - 18 -

19. Applications • Diagnostics • Therapy • 3D • 4D National Taiwan University Electrical Engineering Dept. - 19 -

20. Strengths of Ultrasound • It images muscles and soft tissues well • It’s “Live” • Non-invasive • It has no known long-term side effects, and it causes rarely discomfort to patient National Taiwan University Electrical Engineering Dept. - 20 -

21. Strengths of Ultrasound (cont’d) • Equipment is widely available and flexible • Portable equipment is available, thus it has high mobility • Relatively inexpensive (e.g. X-ray, MRI) National Taiwan University Electrical Engineering Dept. - 21 -

22. Weaknesses of Ultrasound • Very limited ultrasound penetrating ability • Noisy • Low spatial resolution • Operator-dependent National Taiwan University Electrical Engineering Dept. - 22 -

23. Dangers of Ultrasound • Cavitation • Heat generation • Bubble formation National Taiwan University Electrical Engineering Dept. - 23 -

24. 參考資料： www.wikipedia.org/wiki/Wiki www.ljbdev.com/speckle.html http://tw.knowledge.yahoo.com/ http://www.cs.sunysb.edu/~mueller/teaching/ http://ultrasound.ee.ntu.edu.tw/chinese.htm http://ultrasound.ee.ntu.edu.tw/belab/course.htm http://www.gehealthcare.com/inen/rad/us/technology/msuwidap.html 特別感謝： 李百旗 教授 鐘孝文 教授 劉建宏 助教 National Taiwan University Electrical Engineering Dept. - 24 -

25. Thanks for your attention! National Taiwan University Electrical Engineering Dept. - 25 -