Ultrasound

10 Key excerpts on "Ultrasound"

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  eBook - PDF

  Physics of Radiology, 2nd Edition

  • Anthony Wolbarst(Author)
  • 2005(Publication Date)
  • Medical Physics Publishing

    (Publisher)

  Ultrasound Imaging I: Reflections of Acoustic Waves in Elastic Tissues 1. Of Bats and Boats: Getting Around in the Dark 2. Creating Images from Echoes: Medical Ultrasound Is Much like SONAR 3. Sound Is a Mechanical Vibration Propagating through a Medium 4. The Frequency Spectrum of Pulsed Ultrasound Is Continuous 5. The Velocity of Sound in a Medium Is Nearly Independent of the Frequency and Wavelength 6. Intensity of Sound: The W/m 2 and the Decibel 7. Exponential Attenuation of Ultrasound with Depth in a Homogeneous Medium 8. Refraction of Ultrasound at an Interface between Media with Different Acoustic Properties 9. Reflection of Ultrasound at an Interface between Media with Different Acoustic Properties 10. Physical/Biologic Sources of Medically Relevant Ultrasound Information 11. Case Study: Echoes from a Bone Embedded in Tissue 12. Back Down to Earth 114 Chapter 11 For all the other technologies described in this book, the radiation that interacts with body tissues is either ionizing (x- and gamma ray) or r.f. (MRI) electromagnetic energy. Ultrasound (US) radiation consists of something quite dif- ferent: high-frequency sound waves, typically in the 1 to 10 MHz range. Some kinds of vibrations, such as those of a piano string or a piezoelectric element in an Ultrasound transducer, form standing waves. Sound and Ultrasound passing through air, water, or tissue, however, are in the form of traveling waves. Like light, Ultrasound energy is absorbed by any medium through which it passes, and it undergoes refraction and reflection at interfaces between different media. A sharp Ultrasound echo, in particular, will be produced at a sizable and relatively flat boundary between two materials with dif- ferent physical characteristics. It is the production of such echoes at organs, vessels, and other structures that underlies ultra- sound image formation.

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  The Physics of Diagnostic Imaging

  • David Dowsett, Patrick A Kenny, R Eugene Johnston(Authors)
  • 2006(Publication Date)
  • CRC Press

    (Publisher)

  The Ultrasound signal is produced by electrically stimulating a crystalline material to oscillate. Ultra-sound waves obey all the conventional laws associ-ated with light waves except they require a medium (gas, solid or liquid) for their transmission, which takes place by a sequence of compressions and rarefac-tions within the conducting medium (see Chapter 2). 17.1.1 Propagation Sound waves are longitudinal waves and require a medium (gas, liquid, solid) for their transmission. The passage of Ultrasound energy through a medium is illustrated in Fig. 17.2a; the material boundaries or molecules are represented as flat plates connected by massless bonds shown as springs. A longitudinal wave transmits its energy through material by causing the Table 17.1 Frequencies and hearing range of common sounds. Hearing range, or sound Frequency Audible range 15 to 20000 Hz Range for children’s hearing Up to 40000 Hz Male speaking voice 100 to 1500 Hz Female speaking voice 150 to 2500 Hz Middle C 262 Hz Concert A 440 Hz Top C 2093 Hz Bat sounds 50 000 to 200 000 Hz Maximum sound frequency 6 10 8 (600 MHz) Medical Ultrasound 2.5 to 40 MHz molecules in its path to oscillate back and forth paral-lel to the direction of travel of the wave front; oscilla-tions are shown as compressions traveling along the plates. Sound travel first involves molecular or parti-cle vibration (elongation) at the excitation frequency. Sound particle velocity (elongation velocity , in cm s 1 ) is the velocity of a particle about its equilib-rium position ( in Fig. 17.2b). The elongation dis-turbance propagates through the medium (tissue) at a specific propagation velocity c in m s 1 , the absolute speed depending on the medium. A picture of Ultrasound transmission is repre-sented in Fig. 17.2(b) as a row of connected particles. The sound pressure applies a force from the left hand side to particle ‘1’.

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  Handbook of Physics in Medicine and Biology

  • Robert Splinter(Author)
  • 2010(Publication Date)
  • CRC Press

    (Publisher)

  32-13 Additional Reading ......................................................................................................................... 32-13 Robert Splinter 32.1 Introduction and Overview Ultrasound imaging uses sound waves to determine the mechan-ical characteristics of tissue. Sound waves are longitudinal waves that travel through matter using the medium as a carrier for the wave energy . Th is means that sound cannot travel in a vacuum. In lo ngitudinal w aves, t he d irection o f w ave p ropagation i s parallel to t he mot ion of t he me chanism t hat forms t he w ave: particles, mole cules, a nd s o o n. I n c ontrast, ele ctromagnetic waves ( e.g., l ight, x -ray, a nd r adiowaves) a re t ransverse w aves where the electr ic fi eld and the magnet ic fi eld are perpendicular to each other, and the direction of propagation is perpendicular to the wave mechanism itself. Ultrasound waves are represented by medium compression a nd expansion, which form t he crests and valleys, respectively, in t he w ave description, t hat is, pres-sure waves. Figure 32.1 illustrates the compression at the crest of the wave and the expansion at the valley. Sound waves are generally classi fi ed based on the frequency of the waves. Infrasound waves are less than 20 Hz and cannot be heard b y h umans. A udible s ound f alls i n t he r ange b etween 20 Hz and 20,000 Hz. Any sound wave frequency above the limit of human hearing is technically considered Ultrasound. However, diagnostic Ultrasound generally uses f requencies ranging f rom 1 MHz up to 100 MHz. 32.2 Advantages of Ultrasonic Imaging One of the advantages of Ultrasound imaging is that it is rela-tively inexpensive, mainly due to the relatively basic technologi-cal basis of this imaging modality. Ultrasound imaging produces high-resolution i mages t hat r ival a nother rel atively c ommon imaging modality: x-ray imaging, plus it can produce real-time images .

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  eBook - ePub

  Basic Transesophageal and Critical Care Ultrasound

  • André Denault, Annette Vegas, Yoan Lamarche, Jean-Claude Tardif, Pierre Couture, André Denault, Annette Vegas, Yoan Lamarche, Jean-Claude Tardif, Pierre Couture(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 1

  Ultrasound Imaging: Acquisition and Optimization

  Wilfredo Puentes and Annette Vegas

  INTRODUCTION

  This chapter presents a brief description of the basic physical principles of Ultrasound (US), as well as the steps involved in producing an Ultrasound image. Common US probes and key controls on the US machine for acquiring and optimizing the different imaging modes (two-dimensional (2D) and Doppler) are outlined.

  BASIC PRINCIPLES OF Ultrasound

  Sonography comes from the Latin sonus (meaning “sound”) and the Greek word graphien (meaning “to write”). Medical ultrasonography uses high frequency sound waves to create images. To appreciate how this process occurs, it is important to understand some of the concepts related to sound.

  Sound Waves

  Sound is mechanical energy transmitted as longitudinal pressure waves formed by molecular interaction in a medium, and hence cannot occur in a vacuum. As sound waves travel through a medium, each molecule hits another and returns to its original position, creating more dense (compression) and less dense (rarefaction) regions in the medium. Different properties of the sound wave can be described including: cycle, frequency, period, wavelength, amplitude, power, intensity, and propagation speed (Figure 1.1 ).

  A cycle comprises one rarefaction and one compression of the sound wave. Frequency (f) is the number of cycles in a given time, 1 cycle/second = 1 Hertz (Hz). Period (T) is the time it takes for one complete cycle to pass a point or for a wave to travel a distance of one wavelength. Wavelength (λ) represents the horizontal distance between any two successive equivalent points on the wave or the length of one cycle of the wave. Frequency and period are inversely proportional (f = 1/T), thus a higher frequency has a shorter wavelength and period. For instance, a higher frequency probe, such as a transesophageal echocardiography (TEE) probe, is superior to a transthoracic echocardiography (TTE) probe in detecting endocarditis because small vegetations can be missed with TTE. The TTE probe has a lower frequency and consequently a larger and less precise wavelength.

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  Vascular Diagnosis with Ultrasound

  Clinical Reference with Case Studies Volume 1: Cerebral and Peripheral Vessels

  • Michael G. Hennerici, Doris Neuerburg-Heusler(Authors)
  • 2005(Publication Date)
  • Thieme

    (Publisher)

  1 Fig. 1. 1 Schematic drawing of Ultrasound wave 1 Physics and Technology of Ultrasound Basic Ultrasound Physics Sound is mechanical energy that is transmitted through a medium such as air. Periodic changes in air pressure are created by forces acting on air molecules, causing them to oscillate. A pressure wave is trans-mitted from one location to another when vibrating molecules interact with neighboring molecules. This molecular motion is necessary for the transmission of sound and explains why sound cannot be transmitted in a vacuum. Sound waves above a frequency of 20 kHz are termed “Ultrasound.” Like all sound waves, Ultrasound propagates through various media in the form of a pul-sating pressure wave. Waves are basically of two types— longitudinal and transverse. Longitudinal waves are those in which particle motion is along the direction of propagation of the wave energy. Sound waves are longitudinal. Transverse waves are perpendicular to the direction of propagation of the wave energy. Wave motion resulting from a stone being thrown into water is an example of a transverse wave. Bone is the only bi-ological tissue that can cause the production of trans-verse waves, which are also referred to as “shear waves” or “stress waves.” Properties of Waves When particle displacement is plotted against dis-tance, the wavelength ( λ ) of a wave is the distance from crest to crest, or from trough to trough. A wave cycle is a sequence of changes in the amplitude that recur at regular intervals. The frequency ( f ) of a wave is the number of cycles passing a given point in one unit of time (usually one second). The unit of frequency is the hertz (Hz; one cycle per second) (Fig. 1. 1 ). The speed of wave propagation through a medium is known as the acoustic velocity, c . This speed depends on the density and compressibility of a medium. For sound to propagate, it is essential for a medium to be present.

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  Transesophageal Echocardiography Multimedia Manual

  A Perioperative Transdisciplinary Approach

  • André Denault, Pierre Couture, Annette Vegas, Jean Buithieu, Jean-Claude Tardif, André Y. Denault, André Y. Denault, Pierre Couture, Annette Vegas, Jean Buithieu, Jean-Claude Tardif(Authors)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  1 Principles of Ultrasound Alain Gauvin and Guy Cloutier Universite´ de Montre´al, Montreal, Quebec, Canada Michel Germain McGill University, Montreal, Quebec, Canada COMPRESSION AND RAREFACTION Ultrasound consists of mechanical sound waves whose frequencies are above the audible range, that is, 20,000 Hz (Hz stands for the number of wave cycles per second). Sound is defined as a mechanical wave that propagates in a medium due to molecular interaction. The mode of propagation of Ultrasound is related to successive molecular compressions and rarefactions occurring in that medium (Fig. 1.1). When individual molecular motion is in the same direction as the wave propagation, it forms a longitu- dinal wave. When molecular motion is perpendicular to wave direction, it is a transverse (or shear) wave. Solids, such as biological tissues, can experience both transverse (or shear) and longitudinal waves. Ultra- sound in fluids and gases mostly experiences longitu- dinal propagation because of the lack of strong coupling between the molecules. Recent research sug- gests that shear waves may become clinically useful to characterize the viscoelastic properties of biological tissues and be used in sonoelasticity imaging and dynamic elastography. To understand Ultrasound production, one can imagine a small transducer driving an oscillating surface in contact with gas molecules, as illustrated in Figure 1.2. As the surface moves forward, it pushes gas molecules in front of it, creating a zone of compression (Fig. 1.2A). The oscillating surface then retracts, during which time the newly created zone of compression moves forward. However, this backward motion of the surface also causes a rarefaction of local gas molecules (Fig. 1.2B). In the time elapsed between Figure 1.2A and B, the zone of increased density initially created moves forward at propagation speed denoted as c.

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  Principles of Engineering Physics 1

  • Md Nazoor Khan, Simanchala Panigrahi(Authors)
  • 2017(Publication Date)
  • Cambridge University Press

    (Publisher)

  11 Ultrasonics 11.1 Introduction Ultrasonics is the branch of science and technology concerned with the study and use of ultrasonic waves. Sound waves of frequency more than 20 kHz are called Ultrasound. Though these sound waves are not sensed by a normal human ear, they are sensed by a few lower creatures like cats, fox, puppies, nocturnal insects and animals, dolphins, a few variety of whales, and fishes. Sound waves of a frequency less than 20 Hz are called infrasonic. Though infrasonic sound waves are not audible to us, it sometimes gives us a sensation of “ghost vision”. Elephants use infrasound for their communication. In addition to the properties of audible sound waves, ultrasonic waves exhibit other new phenomena. Ultrasonic waves have a large number of applications in all fields of science and technology. The Ultrasound is used in many different fields, typically to penetrate a medium and measure the reflection signature or supply focused energy. The reflection signature can reveal details about the inner structure of the medium. 11.2 Production of Ultrasonic Waves Unlike audible sound waves (20 Hz–20 kHz), production of ultrasonic waves requires special devices and methods. In the following, we shall discuss few methods of production of ultrasonic waves. 11.2.1 Galton’s whistle Galton’s whistle (also known as silent whistle or dog whistle) is a type of whistle that emits sound in the ultrasonic range. It was invented in 1876 by Francis Galton and is used in the Ultrasonics 765 training of dogs and cats. It is believed that the wild ancestors of cats and dogs evolved this hearing range in order to hear high frequency sounds made by their preferred prey, small rodents. Principle Galton's whistle works on the principle of the organ pipe. In a close ended organ pipe, resonance occurs when the length of the pipe is one-fourth times the length of the wavelength of sound in the air medium, i.e., 4 λ =  .

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  eBook - ePub

  Revival: CRC Handbook of Ultrasound in Obstetrics and Gynecology, Volume I (1990)

  • Asim Kurjak(Author)
  • 2019(Publication Date)
  • Taylor & Francis

    (Publisher)

  Chapter 1 BASIC PRINCIPLES OF ULTRASONIC IMAGING Branko Breyer and Željko Andreić INTRODUCTION

  In this chapter we shall describe basic physical and technological principles of Ultrasound diagnostic equipment without extensive mathematical treatment, except for some simple and useful formulas. These formulas are usually supported by worked examples and comments relevant for practical use. Ultrasound diagnostic instruments and procedures are developing rapidly, so that mere knowledge of manipulation with the existing instruments is definitely insufficient for sound usage of the instruments to come. On the other hand, the knowledge of underlying physical principles allows one to understand what is actually new in an instrument, what the supposed advantages are, and how they can be exploited in practical work.

  PHYSICAL PRINCIPLES BASIC CONCEPTS OF WAVES AND SOUND

  Sound is mechanical vibration which spreads from its source into the surrounding medium. Such spreading mechanical vibrations are called waves, mostly because in many ways they resemble waves on the water surface. For instance, if we disturb calm water, say, with a wooden stick which we move up and down, water waves will form and spread radially away from the stick. In an analogous way, sound waves are produced by disturbing the air somehow, and they spread in all directions away from their source. When we speak about sound waves, we intuitively think about audible sound which we can hear and which spreads in air. Sound waves can also exist in other media and can be totally imperceptible to us. What is common to all “sound” waves is that they can be described by the same laws of nature.

  The vibrating object which produces the sound is called the source. This source is somehow made to vibrate, and its vibrations disturb the medium around it. The produced disturbances spread away through the medium around the source in the same way the water waves spread around the moving stick. If we look at the water waves more carefully, we will see that the water itself does not flow. It just moves up and down, and the movements travel from the stick outwards. This can be verified by a simple experiment. If we put a few small chips of wood on the water surface and watch their movements as the wave passes by, we can see the chips moving up and down while the wave is passing by them, but after the wave is gone, they are again at rest at their original positions. So, only the disturbance travels through the water, while water itself stays at rest. This traveling disturbance is called a wave, and under normal circumstances it produces no flow of medium through which it spreads. In audible sound waves, air molecules are moved back and forth around their positions in the direction of wave spreading. Such a wave is called a longitudinal wave. All sound waves in normal circumstances are longitudinal. In some cases, transversal waves or waves with complicated particle motions can exist, but we shall limit our discussion only to the longitudinal sound waves because only such waves are used for therapeutic and diagnostic applications.

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  Non-Destructive Testing

  And Testability of Materials and Structures

  • Gilles Corneloup, Cécile Gueudré, Marie-Aude Ploix(Authors)
  • 2021(Publication Date)
  • PPUR

    (Publisher)

  The very high sensitivity of propagation to the rates Fig. 7.1 Principle of Ultrasound testing and representation of echoes 124 Non-Destructive Testing of heterogeneity or anisotropy of the material or to the environment (temperature, state of stress, etc.), is also an inconvenience in industrial inspections. But it is also thanks to these factors that the measurement of one parameter is possible; this proves that ultrasonic testing is, without a doubt, the most efficient method of non-destructive characterization of materials and structures. 7.1 PHYSICAL PRINCIPLES 7.1.1 Ultrasound The frequency range of sound waves is from hertz to gigahertz. (Audible) sounds go from 15 Hz to 15–20 kHz, and Ultrasound, inaudible for humans, covers the field from 20 kHz. In industrial inspection, frequencies from 1 to 10 MHz are usually used. For frequencies higher than 50 MHz, we talk about acoustic microscopy. An ultrasonic wave refers to the vibrating displacement of a medium that leads to local pressure changes in the case of fluids or stresses in the case of solids. The mea- surement or observation of the propagation of these variations allows a better unders- tanding of the medium, and it is on this principle that ultrasonic testing is based. Testing is non-destructive because the vibration amplitude is small. 7.1.2 The propagation of ultrasonic waves in perfect (ELHI) media Propagation models used generally assume that waves are plane (the wavefronts of a plane wave are theoretically infinite planes) and monochromatic (one single fre- quency). The first hypothesis is accessible, but the impulse mode (a wide range of frequencies) is often favored in NDT: the associated temporal signal is short and gives a temporal resolution (which will in practical terms better locate a defect in depth). So, even if the theory is not respected, its study helps us understand the main tendencies of Ultrasound behavior.

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  Advances in Biomedical Engineering

  Published Under the Auspices of the Biomedical Engineering Society

  • J. H. U. Brown, James F. Dickson(Authors)
  • 2014(Publication Date)
  • Academic Press

    (Publisher)

  To fully appreciate the advantages and limitations of Ultrasound as 219 220 J. Ε. JACOBS a diagnostic aid, the discussion that follows describes the material char-acteristics that determine the propagation of Ultrasound, the commonly used techniques for instrumentation involving Ultrasound, documented applications regarding the diagnostic capability of Ultrasound, and an evaluation of hazards associated with its use. II. F U N D A M E N T A L S OF Ultrasound PROPAGATION The term ultrasonics has been applied to sonic energy having frequencies greater than that to which the human ear can respond. In discussions of the application of ultrasonics to biological problems, it is convenient to divide these into those concerned with low-energy and high-energy sound fields. A low-energy field is defined as one that does not result in permanent changes in the medium through which the Ultrasound is propagated. High-energy fields are those that use Ultrasound energy of a sufficiently high level that permanent changes in the medium resulting from propagation of the Ultrasound are observed. All diagnostic instru-ments operate at low-energy levels as described in the following section. A. Characteristics of Low-Energy Ultrasound Interaction with Biological Tissue Low-energy Ultrasound, by definition, does not in any way affect the physical properties of the material through which it is propagating. Through the use of low-level Ultrasound, it is possible to measure the velocity and absorption coefficients of a given material and by these measurements completely characterize the mode of propagation in a given medium. Since low-energy Ultrasound waves are, by definition, waves having an amplitude such as there is a linear relationship between the applied stress and the resultant strain, the absorption coefficients obtained are essentially based on a series of linear measurements.

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