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Outline. What is ultrasound Ultrasonic signal generation Diagnostic Ultrasound Ultrasound imaging A rray systems, Co-Arrays, K-space Beamformers Biosensors Theraupatic Ultrasound Effect of US->Heating, vibrating,etc . US power transmission and the applications

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  1. Outline • What is ultrasound • Ultrasonic signal generation • Diagnostic Ultrasound • Ultrasound imaging • Array systems, Co-Arrays, K-space • Beamformers • Biosensors • Theraupatic Ultrasound • Effect of US->Heating, vibrating,etc. • US power transmission and the applications • Doppler effect and the applications • Microfluidics applications

  2. What is Ultrasonic wave? • Wave, a wave is a disturbance or oscillation that travels through space and matter, accompanied by a transfer of energy. Wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium. • There are two main types of waves: • Mechanical Waves: Propagate through a medium, and the substance of this medium is deformed. • Electromagnetic Waves: do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles

  3. Mechanical Waves • Longitudinal Wave: wave particles vibrate back and forth along the path that the wave travels. • Compressions: The close together part of the wave • Rarefactions: The spread-out parts of a wave

  4. Mechanical Waves • Transverse Wave: wave particles vibrate in an up-and-down motion. • Crests: Highest part of a wave • Troughs: The low points of the wave

  5. Wave Properties • In liquids and gases, US propagates as longitudinal waves. • In solids, US propagates also as transversal waves. • Amplitude: is the maximum distance the particles in a wave vibrate from their rest positions. • Frequency : the number of waves produced in a given time

  6. Wave Properties Frequency= #ofwaves/time

  7. Wavelength: The length of a single wave. • #ofwaves = (Total displacement in a given time) / (The length of a single wave) • => Frequency = Total displacement/wavelength*Time) • Wave Velocity - is the speed with which a wave crest passes by a particular point in space. (wave velocity=Total displacement/time). It is measured in meters/second. • Result: Wave Velocity = Frequency  Wavelength

  8. Speed of Sound • Medium velocity m/sec air (20 C) 343 air (0 C) 331 water (25 C) 1493 sea water 1533 diamond 12000 iron 5130 copper 3560 glass 5640

  9. Speed of Sound Waves In gas and liquids: In solids: Y… Young’s modulus B… Bulk modulus of medium r…density of material Young’s modules determines the length change of an object due to an applied force F. Bulk modules determines the volume change of an object due to an applied pressure P.

  10. Ultrasound - sound waves with frequencies above the normal human range of hearing. Sounds in the range from 20-100kHz Infrasound - sounds with frequencies below the normal human range of hearing. Sounds in the 20-200 Hzrange

  11. Types of US Waves • Bulk Waves: 3 Dimensional propagation • Guided waves: Propagates at surfaces, interfaces and edges. (Surface Acoustic Waves). Reigleigh wave. Lowe Wave Shear Horizontal Wave etc.

  12. Interference • the result of two or more sound • waves overlapping

  13. Diffraction • No-one has ever been able to define the difference between interference and diffraction satisfactorily. It is just a question of usage, and there is no specific, important physical difference between them. Richard Feynman

  14. Interactions of US with Tissue • Reflection (smooth homogeneous interfaces of size greater than beam width, e.g. organ outlines) • Rayleigh Scatter (small reflector sizes, e.g. blood cells, dominates in non-homogeneous media) • Refraction (away from normal from less dense to denser medium, note opposite to light, sometimes produces distortion) • Absorption (sound to heat) • absorption increases with f, note opposite to X-rays • absorption high in lungs, less in bone, least in soft tissue, again note opposite to x-rays

  15. Acoustic parameters of medium: • Interaction of US with medium – reflection and back-scattering, refraction, attenuation (scattering and absorption)

  16. Acoustic parameters of medium Speed of US c depends on elasticity and density r of the medium: K - modulus of compression in water and soft tissues c = 1500 - 1600 m.s-1, in bone about 3600 m.s-1

  17. Acoustic parameters of medium Attenuationof US expresses decrease of wave amplitude along its trajectory. It depends on frequency Ix = Io e-2ax = ´.f2 Ix – final intensity, Io – initial intensity, 2x – medium layer thickness (reflected wave travels „to and fro“),  - linear attenuation coefficient (increases with frequency). Since a = log10(I0/IX)/2x we can express  in units dB/cm. At 1 MHz: muscle 1.2, liver 0.5, brain 0.9, connective tissue 2.5, bone 8.0

  18. attenuation I or P [dB] depth[cm] Acoustic parameters of medium Attenuation of ultrasound When expressing intensity of ultrasound in decibels, i.e. as a logarithm of Ix/I0, we can see the amplitudes of echoes to decrease linearly.

  19. Acoustic parameters of medium Acoustic impedance: product of US speed c and medium density r Z =  . c (Pa.s/m) Z.10-6: muscles 1.7, liver 1.65 brain 1.56, bone 6.1, water 1.48

  20. Acoustic parameters of medium:US reflection and transmission on interfaces We suppose perpendicular incidence of US on an interface between two media with different Z - a portion of waves will pass through and a portion will be reflected (the larger the difference in Z, the higher reflection). P1 Z 2 - Z 1 R = ------- = --------------- P Z2 + Z1 P2 2 Z 1 D = ------- = --------------- P Z2 + Z1 Coefficient of reflection R – ratio of acoustic pressures of reflected and incident waves Coefficient of transmission D – ratio of acoustic pressures of transmitted and incident waves

  21. Acoustic parameters of medium:Near field and far field • Near field (Fresnel area) – this part of US beam is cylindrical – there are big pressure differences in beam axis • Far field (Fraunhofer area)– US beam is divergent – pressure distribution is more homogeneous • Increase of frequency of US or smaller probe diameter cause shortening of near field - divergence of far field increases

  22. The adjacent points pressures effect each other. This effect is less in far field.

  23. Feynman derives the wave equation that describes the behaviour of sound in matter in one dimension (position x) as: • Provided that the speed c is a constant, not dependent on frequency (the dispersionless case), then the most general solution is:

  24. where f and g are any two twice-differentiable functions. This may be pictured as the superposition of two waveforms of arbitrary profile, one (f) travelling up the x-axis and the other (g) down the x-axis at the speed c. The particular case of a sinusoidal wave travelling in one direction is obtained by choosing either f or g to be a sinusoid, and the other to be zero, giving: • Where omega is the angular frequency of the wave and k is its wave number.

  25. 3D Wave Eq. • Solution in cartesian coordinates:

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