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...
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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
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History
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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
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Principle – Focusing
Lateral Resolution = D = depth, W = wavelength, A = Aperture
F number, F# =
Ex: f=5Mhz, A = 2cm, V = 1500 m/sIn depth 4 cm,
resolution =
A
WD
A
D
36
106.02
1051500
4
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Principle – Focusing (cont’d)
Improve larger aperture higher frequency (shorter wavelength) multiple focusing dynamic focusing
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Principle – Focusing (cont’d)
Improve larger aperture higher frequency (sho
rter wavelength) multiple focusing dynamic focusing
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Principle – Focusing (cont’d)
Improve larger aperture higher frequency
(shorter wavelength) multiple focusing dynamic focusing
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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
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Principle – Speckle
Coherent Imaging system
Interference of scatterers
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Principle – Speckle
Scatter size (radius a) Wavelength (λ) Wave number K=2π/λ
Optical : ka>>1 Rayleigh : ka<<1 Oscillatory : between
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Principle – Speckle
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Rayleigh : ka<<1
Principle – Speckle Soft tissue : less than 100μm
Independent of scattering structures
Dependent of imaging system 、 distance
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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:
N
i
ijiea
NA
1
1
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Principle – Speckle
Intensity I≡ Re{ A }2 +Im{ A } 2
1I
I
ISNR
So for I 0:≧
And amplitude E≡ is Rayleigh distribution:
91.1E
E
ESNR
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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
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Characteristic
ModesA modeB modeM modeColor Doppler mode
Acoustic impedance
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Characteristic – Modes
A mode B mode M mode CPD
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Applications
Diagnostics Therapy 3D 4D
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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
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Strengths of Ultrasound (cont’d)
Equipment is widely available and flexible Portable equipment is available, thus it ha
s high mobility Relatively inexpensive (e.g. X-ray, MRI)
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Weaknesses of Ultrasound
Very limited ultrasound penetrating ability Noisy Low spatial resolution Operator-dependent
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Dangers of Ultrasound
Cavitation Heat generation Bubble formation
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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
Thanks for your attention!
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