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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