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.

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

History National Taiwan University Electrical Engineering Dept 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

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

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 -

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

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

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

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 -

Principle – Speckle Coherent Imaging system Interference of scatterers National Taiwan University Electrical Engineering Dept

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

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

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

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

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

Principle – Speckle Define: I 0 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

Characteristic Modes  A mode  B mode  M mode  Color Doppler mode Acoustic impedance National Taiwan University Electrical Engineering Dept

Characteristic – Modes A mode B mode M mode CPD National Taiwan University Electrical Engineering Dept

Applications Diagnostics Therapy 3D 4D National Taiwan University Electrical Engineering Dept

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

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

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

Dangers of Ultrasound Cavitation Heat generation Bubble formation National Taiwan University Electrical Engineering Dept

National Taiwan University Electrical Engineering Dept 參考資料： 特別感謝： 李百旗 教授 鐘孝文 教授 劉建宏 助教

Thanks for your attention! National Taiwan University Electrical Engineering Dept