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In the name of GOD

In the name of GOD. Chapter 1 Basic Ultrasound Physics. Tavakoli. M.B, Isfahan University of Medical Sciences, School of Medicine Department of Medical Physics and Medical Engineering. بنام خدا. نام و شماره درس : فراصوت و كاربرد آن تعداد و نوع واحد : سه واحد نظري

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In the name of GOD

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  1. In the name of GOD Chapter 1 Basic Ultrasound Physics Tavakoli. M.B, Isfahan University of Medical Sciences, School of Medicine Department of Medical Physics and Medical Engineering

  2. بنام خدا • نام و شماره درس:فراصوت و كاربرد آنتعداد و نوع واحد:سه واحد نظري • گروه سرويس دهنده:گروه فيزيك و مهندسي پزشكي گروه سرويس گيرنده:گروه فيزيك • رشته و مقطع تحصيلي:روز و ساعت • محل برگزاري:گروه فيزيك و مهندسي‌پزشكي • سال تحصيلي: • نام مدرس:دكتر محمدباقر توكلي • آدرس دفتر:دانشكده پزشكي – گروه فيزيك و مهندسي پزشكي mbtavakoli@mui.ac.ir Email: • هدف كلي درس:آشنائي با مباني و اصول فراصوت و كاربرد آن در پزشكي • اهداف اختصاصي: • -1 آشنايي با مباني فيزيكي التراسوند • -2آشنايي با سيستم‌هاي التراسونيكي • -3 آشنايي با روشهاي تكنيكي التراسونيكي • -4آشنايي با اثرات بيولوژيكي التراسوند • برنامه درسي در هر جلسه: • جلسه اول:اصول فيزيكي صوت و التراسوند • جلسه دوم: پراكنش و تضعيف التراسوند در مواد • جلسه سوم:ساختمان ترانسدوسر و ويژگي‌هاي ترانسدوسرها • جلسه چهارم: روشهاي ايجاد تصوير بطريقه استاتيك • جلسه پنجم: روشهاي تصويرگيري real time • جلسه ششم: روشهاي تصويرگيري real time • جلسه هفتم: پروسس تصوير و عوامل مؤثر در كيفيت آن • جلسه هشتم: آرتي‌فكت ها در سونوگرافي • جلسه نهم: اصول فيزيكي روش داپلر • جلسه دهم:‌ ارزيابي تصاوير داپلر

  3. جلسه ياازدهم: روش M-Mode • جلسه دوازدهم: مواد حاجب در التراسوند • جلسه سيزدهم: اثرات بيولوژيكي • جلسه چهاردهم:ملاحظات كلينيكي • جلسه پانزدهم: كنترل كيفي و ارزيابي سيستم‌هاي التراسونيكي • جلسه شانزدهم: دستگاههاي درماني فراصوتي • منابع اصلي درس: • 1- Headrick et al , Ultrasound Physics and Instrumentation, Diagnostic • 2- Fish P.S Physics and Instrumentation of Medical Ultrasound, Tohn Willy and Sons • 3- Bushong SC and Archer BR. Diagnostic Ultrasound Physics, Biology and Instrumentation, Mosby, Yearbook, London • -4روشهاي پيشرفته تصويربرداري ، دكتر محمدباقر توكلي ، انتشارات دانشگاه علوم پزشكي • نحوه ارزشيابي: • الف) حضور در كلاس و انجام تكاليف كلاسي و شركت درمباحث كلاس 2 نمره • ب) امتحان ميان ترم 8 نمره • ج ) امتحان پايان ترم 10 نمره

  4. Basic Ultrasound Physics continue • Sound Wave: Is a type of mechanical energy that is transmitted through medium. • Propagation: Sound wave propagate through deformation of the elastic medium • Sound wave spectrum: Is divided into three region ofInferasound(f<20Hz); Sound (f=20 to 20000Hz) and Ultrasound (f>20kHz) • Wave equation: A=A0sin (ωt+θ) A=amplitude; A0=Maximum amplitude; θ=initial phase and ω =2пf f=1/T

  5. Basic Ultrasound Physics continue • Types of sound wave: • Longitudinal • Shear wave • Compressibility: The fractional decrease in volume when pressure applied to the material. • Bulk modulus=-stress/strain • The reciprocal of compressibility is bulk modulus • β(bulk modulus)=1/ K (compressibility of medium)

  6. Sound velocity • Sound velocity • c(m./sec)=f(1/sec or Hz)λ(m) • Sound velocity depends on compressibility (K) • c=1/(Kρ)1/2=(β/ ρ)1/2 In materials with higher compressibility velocity of sound is less and Vic versa

  7. Typical values for diagnostic ultrasound: • Ultrasound f > 20KHz • f : 1 to 10 MHz • λ : 1.5 to 0.15 mm in muscle • I (Acoustic Intensity)< • Acoustic Pressure P<0.57 bar • Units : Pascal (Pa) 1Pa=1N/M2=10μbar • Particle velocity v<3.5 cm/s • Elongation ξ < 2*10-6 • Particle acceleration < 7*104 g

  8. Acoustic Impedance • Z is the acoustic impedance • Acoustic Pressure: P=Zv • It can be show that

  9. Interaction of ultrasound with tissue • Reflection • Refraction • Diffraction • Scatter • Absorption

  10. Reflection • According to Snell laws • 1-Incident and reflected angles are equal αi =θr • 2-the relation between incident and transmission angles is: Sinαi/ Cosαt=c1/c2 • 3-All of the incident reflection and transmitted rays are in the same plane • Energy transmission and reflection percentages are:

  11. For specular reflection: Amplitude reflection coefficient r : • Energy transmitted and reflection coefficient t : The continuity condition is: R+T=1

  12. Scattering Is = Intensity of scattered sound σ = Scattering cross section When a<λ then Rayleigh scattering=>Iαf2 to f6

  13. Refraction Sinαi/ Cosαt=c1/c2

  14. Diffraction • Diffraction cause ultrasound beam to diverge • The rate of divergence increase with diameter of the source

  15. Interference • Sound wave demonstrate interference phenomena • If they are in phase and with the same frequencies=>instructive effect • If they are out of phase and or with different frequencies=>destructive effect

  16. Absorption • The only process that sound energy dissipate in medium • Factors influencing absorption: • Frequency of the sound • Viscosity of the medium • Relaxation time of the medium

  17. Absorption Jz=J0e-2βz J= ultrasonic intensity at depth z J0= ultrasonic intensity at depth0 β = absorption coefficient in Np/cm • Attenuation coefficient=α=2 β • α attenuation coefficient in dB

  18. In biological tissue usually • β0= 0absorption coefficient at f0(1 MHz) • Relative absorption attenuation usually given by

  19. Spectrum • Displaced of particle around the rest position mechanical phenomena v= velocity of motion ξ = elongation Basic Physics • Acoustic pressure : difference between pressure at any line and normal state Units : Pascal (Pa) 1Pa=1N/M2=10μbar

  20. Propagation velocity = C E = modulus of elasticity ρ = density of rest • C =λf • Acoustic Pressure: P=Zv • It can be show that

  21. For a particular particle velocity, the greater impedance, the greater the acoustic pressure that has to be generated. • Power Density : Infautaneous power passing through a unit area is :

  22. Typical values for diagnostic ultrasound: • Ultrasound f > 20KHz • f : 1 to 10 MHz • λ : 1.5 to 0.15 mm in muscle • J (Acoustic Intensity)< • Acoustic Pressure P<0.57 bar • Particle velocity v<3.5 cm/s • Elongation ξ < 2*10-6 • Particle acceleration < 7*104 g

  23. Wave equation and the plane wave For a plan wave using Newton’s second low for a mass m and spring force k(z) and k(z+Δz) :

  24. Wave equation and the plane wave

  25. Wave equation and the plane wave

  26. Wave equation and the plane wave

  27. Physical effects • Reflection • Refraction • Diffraction • Scatter • Absorption

  28. Reflection The continuity condition is:

  29. Refraction • Diffraction

  30. Scattering Pa = Intensity of scattered sound σ = Scattering cross section

  31. Transmission For dynamic case in the region of resonance frequencies Kτ=0.5 for good transducer

  32. Transducer factors • k = Electromechaanical coupling coefficient • h = Transmission coefficient • g = Reception coefficient k=hg • ε = Dielectric constant • depends on electric and mechanical properties of transducer. It is important in strain of the transducer. • Transducer sensitivity depend of reception coefficient and strain and ε.

  33. Matching layer • Zω(matching layer impedance)=antilog • Thickness = m λ/4 • Quality factor (Q)

  34. Acoustic beam : must be as narrow as possible with sharp fall off at the edges • The intensity in front of a piston transducer • Sound pressure from each element interfere with each other • Make a near field ( Fernel zone) and far field ( Franhofer zone) at boundary Z=a2/λ • Beam angle at the boundary • Natural focus ( between far and near field) at Zf with focal diameter df

  35. Image limitation • Penetration depth • Signal dynamic • Special resolution

  36. Ultrasonic technique • Pulse echo • Real time • A-scan • B-scan • M-mode • Doppler

  37. A-scan Main part • Clock pulse repetition frequency (PRF) • Ultrasonic velocity • Depth of investigation • Number of line per image • Filter • Transmitter • Receiver • TGC+Amplifier • Radio Amp. • Video Amp. • Time generator • Processing

  38. B-scan • One dimension • Two dimension

  39. M-mode

  40. Commercial system • Mechanical • Linear • Sector • Electrical • Linear • Sector

  41. Mechanical sector scanner • Advantages • Simple • Cheap • Acceptable resolution • Disadvantage • Noise • Mechanical fracture • Reverberation • Sector field

  42. Electronic Scanners • Linear Typical values: • Number of elements 60-120 • Elements width (b) 1-4 λ • Frequency 3.5-7MHz • Length of ceramic (L) 2-11.5 cm • Scanning length (image width) 2-10 cm

  43. Sector Electronic focusing

  44. Velocity determination • Optimum frequency for doppler is f0=90/R R = soft tissue distance from target • Suitable frequency=2 MHz for deep 5-7 MHz for superficial • Doppler examination • continues wave • pulse wave

  45. C.W doppler • Need two transducer • Can not be used for range resolution • Filter • High pass filter • Low pass filter T Oscillator R RF Amp. Demodulator Audio Amp. Filter Output Device

  46. Pulse wave doppler • Use pulse • Select depth of interest

  47. Oscillator clock Transmit Gate T Instrument design of P.W doppler Range Delay RF Amp. R Length Delay Demodulator Receive Gate Samplet Hold Audio Amp. Filter Out put Device

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