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 آن تعداد 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
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 نمره
ج ) امتحان پايان ترم 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 of Inferasound (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. J= ultrasonic intensity at depth z J0= ultrasonic intensity at depth0
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. Basic Physics mechanical phenomena Spectrum
Displaced of particle around the rest position
v= velocity of motion
ξ = elongation
Acoustic pressure : difference between pressure at any line and normal state Units : Pascal (Pa) 1Pa=1N/M2=10μbar

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

22. 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 :

23. 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

25. 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) :

26. Wave equation and the plane wave

27. Wave equation and the plane wave

28. Wave equation and the plane wave

29. Physical effects
Reflection
Refraction
Diffraction
Scatter
Absorption

30. Reflection
The continuity condition is:

31. Refraction
Diffraction

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

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

34. Transducer factors k=hg 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.

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

36. 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

38. Image limitation
Penetration depth
Signal dynamic
Special resolution

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

40. 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

41. B-scan
One dimension
Two dimension

42. M-mode

43. Commercial system
Mechanical
Linear
Sector
Electrical

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

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

46. Sector Electronic focusing

47. 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

48. 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

49. Pulse wave doppler
Use pulse
Select depth of interest

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

51. Velocity detection limit

52. Directional method Single side band detector High Pass Filter Mixer
Forward
Direction
Amp.
Ref. signal
Low Pass
Filter
Mixer
Side Band
Filter
Reversed
Direction

53. Directional method Heterodyne detector Mixer Channel A Filter In phase
Ref. Signal
Out of phase
Amp.
Mixer
Filter
Channel B

54. Quadratic phase detector
Pilot Frequency
in phase
Channel B
Mixer
Out put
Adder
Mixer
Channel A
Pilot Frequency
Out of phase

55. Color flow imaging
Duplex scanners
spectral Analysis
Power spectrum

56. Doppler systems

57. Quality controls (Q.A)
Axial resolution
Lateral resolution
Penetration depth and sensitivity
Dynamic range
Accuracy
Hand copy performance

58. Biological effects

60. ULTRASOUND Tavakolli.M.B,PhD Medical University of Isfahan
Faculty of Medicine
Department of Medical Physics and Engineering

61. Basic Physics
Mechanical Phenomena
Sound wave
Spectrum
Velocity of sound
Transmission through a barrier
Attenuation
Production and detection
Ultrasonic field in front of a transducer
Resolution
Ultrasonic systems