6 Key excerpts on "Applications of Ultrasound"

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  eBook - ePub

  Handbook of Nuclear Medicine and Molecular Imaging for Physicists

  Radiopharmaceuticals and Clinical Applications, Volume III

  • Michael Ljungberg(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  Ultrasound is a modality that is real-time, cost-efficient, and portable (nowadays even with a transducer connecting wirelessly to a smartphone or tablet). The real-time functionality makes the image available at the same instant as the transducer touches the patient, and it provides immediate feedback to the operator as to how the anatomy relates to the movement of the operator’s hand. This is, however, also one of the drawbacks, the user dependence: How the image is acquired is in the hands of the operator. For this reason, images or image sequences are not stored to the same extent as for other modalities, such as computed tomography, and if so, for documentation purposes. Still, ultrasound is a very useful technique and technology development constantly pushes ultrasound to new applications, such as non-invasive sensing of tissue stiffness (elastography) and developing areas such as measurements of electromechanical activity in the heart, super-resolution imaging, nerve stimulation, photoacoustics, and other approaches for molecular imaging.

  This chapter outlines the basic physical background for ultrasound imaging and some recent technical advances, together with some application areas that are relevant for medical physicists.

  22.2 ULTRASOUND PHYSICS AND TECHNOLOGY

  Ultrasound (i.e., sound at frequencies higher than what the human ear can perceive) is a distinction made by man. As a matter of fact, physically, ultrasound is no different from sound at audible frequencies, being vibrations transmitted in a medium. However, for practical reasons, when we speak of audible sound we mean sound with frequencies in the range of 20–20000 Hz, while lower-frequency sounds are referred to as infrasound, and those with higher, ultrasound.

  The basic principle of ultrasound imaging is very simple, indeed. The fact is, that animals such as bats and dolphins have used this technique for millions of years. It is based on what is called the pulse-echo principle, whereby a short pulse (or shriek, if you will) is emitted, and the time until the return of an echo, is proportional to the distance to the structure from which the sound is reflected – given that the sound speed is known and constant in the medium.

  First of all, one could ask why the animals use ultrasound and not sound in the audible range. The principle actually works just as fine for lower frequency sounds, but the answer lies in the need for the animal to locate the target of their interest more precisely, for instance for food. We have all probably noted that bass speakers are quite insensitive in terms of their location, while tweeters are more directional. This is a result of the fact that with increasing frequency, the number of wavelengths that fit over the speaker membrane also increases. Conversely, if a sound has a low frequency, and thereby long wavelength, the speaker becomes relatively smaller and behaves more like a point source, so that the sound becomes omnidirectional. In other words, dolphins can make the sound beam narrower, to be more like a beam from a flashlight, by increasing the frequency. At the same time a shriek in itself can be made shorter (for a given number of cycles), which facilitates the separation of echoes originating from structures at nearly the same distance from the sound source. To sum up, the higher the frequency, the “sharper” the surrounding can be perceived, as a narrower beam allows better pinpointing from which direction a certain echo comes from and, with higher frequency, shorter pulses can be achieved that are better for distinguishing at what depth the target is. This is precisely the rationale to use ultrasound for diagnostic purposes – to increase the resolution – but here frequencies are even higher, in the MHz range. The practical factor as to why even higher frequencies are not used, is attenuation: Higher frequencies are attenuated more heavily, which sets the upper bounds for the selected frequency. Thereby is also the explanation for the large variety of probes used: For each application the resolution/penetration depth trade-off has been optimized.

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  eBook - ePub

  Ultrasound in Assisted Reproduction and Early Pregnancy

  • Arianna D'Angelo, Nazar N. Amso, Arianna D'Angelo, Nazar N. Amso(Authors)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  2   Basic and Technical Aspects of Ultrasound   Neil D. Pugh   Introduction

  Ultrasound has found many uses in medicine, from diagnosis to therapy in a wide range of specialties. Ultrasound is particularly useful in the field of reproductive medicine; it has advantages over other imaging modalities in that it is quick, inexpensive, noninvasive, and importantly, does not use ionizing radiation. Hence, ultrasound is perfectly suited to reproductive medicine where the risk of teratogenic effects needs to be avoided at all costs.

  The purpose of this chapter is to discuss the principles and technical aspects of ultrasound, so that users are equipped with the appropriate knowledge to enable them to “drive” an ultrasound machine in such a way as to perform a competent ultrasound scan. To this end, this chapter covers the following topics:

  • The basic principles of sound

  • The generation of ultrasound

  • The interactions of ultrasound with tissue

  • Real-time B-mode imaging

  • The basic principles of Doppler ultrasound

  • Machine controls and image optimization

  • Safety of ultrasound

    Basic Principles of Sound

  Sound is a pressure wave, that is a mechanical disturbance of a medium, which passes through the medium at a fixed speed. Sound travels through the medium as a series of molecular vibrations, and the speed at which sound travels through the medium depends on the nature of the medium (solid, liquid, or gas). As the position of the molecules can be fixed, particularly in solids, the molecular vibrations travel as a “wave” through the medium, away from the vibrating source. In other words, sound is a variation in pressure, with regions of increased pressure known as the compression part of the wave and regions of decreased pressure known as the rarefaction portion of the wave. In addition, sound is a longitudinal wave, which means that disturbance is in the same direction as that of the propagation of the wave.

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  eBook - ePub

  AAGBI Core Topics in Anaesthesia 2012

  • Ian Johnston, William Harrop-Griffiths, Leslie Gemmell, Ian Johnston, Leslie Gemmell, William Harrop-Griffiths(Authors)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  CHAPTER 1

  The Physics of Ultrasound Graham Arthurs Maelor Hospital, Wrexham, UK

  Key points

  • Ultrasound is a high-frequency pressure energy wave transmitted longitudinally through the soft tissues of the body.
  • Advances in computer technology have made medical ultrasound possible by processing millions of signals every second.
  • Ultrasound makes it possible to examine most of the tissues of the body safely and easily.
  • The pressure, energy and heating effects of clinical ultrasound devices have not been shown to damage normal biological tissues.
  • The ultrasound wave must be reflected off a tissue interface at right angles. This means that a combination of good hand–eye coordination and correct positioning of the probe is the basis of a good image.
  • Images are presented as patterns on a greyscale monitor. Pattern recognition is therefore the basis of the interpretation of these images.
  • The B or brightness mode gives a greyscale image that is distorted because of a loss of reflected echoes by scatter and refraction.
  • Doppler shift is caused by a change in wavelength when fluid such as blood is moving towards or away from the ultrasound wave.

  This chapter aims to give an introduction to the basic physics of ultrasound in order to allow the reader to understand how images are produced and hence how to obtain the best images when using ultrasound. Clinical ultrasound devices simultaneously produce and transmit multiple pressure waves, and receive and rapidly interpret the many attenuated, returning pressure wave signals. The pressure wave signals are converted into electrical signals. The production of an image in real time by a portable scanner has only become possible with the development of the microprocessor chip. A modern ultrasound device has a lot of computing power with many microprocessors performing many billion operations per second, which makes it possible to build up complicated images in real time. In the near future, smaller processors will enable more precise images to be created on smaller, lighter and cheaper devices.

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  eBook - ePub

  Practical Veterinary Diagnostic Imaging

  • Suzanne Easton(Author)
  • 2012(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Chapter 19 Introduction to Ultrasound

  Chapter contents Sound waves Ultrasound How ultrasound works Types of ultrasound scan Doppler ultrasound Effects on tissue Ultrasound machines and transducers Patient preparation Areas suitable for examination Further reading

  Key points

  • Ultrasound is high-frequency sound waves in the Megahertz (MHz) range
  • Ultrasound is a form of non-ionising radiation
  • Sound waves are created by the piezoelectric effect
  • The sound waves are transmitted into the body and reflected back in varying amounts from an anatomical interface and these reflected waves are detected to produce an image
  • Modern ultrasound machines contain a computer that generates the images and can send them either to film or a picture archiving communication system
  • Ultrasound transducers have different frequencies and are usually in the range of 1–20 MHz
  • The higher the frequency, the better the resolution, but poorer the penetration

  Introduction

  Ultrasound was originally developed during World War I to track submarines as SONAR technology (SOund, Navigation And Ranging). Ultrasound was first used medically in the 1950s. It rapidly became available in the veterinary field and is now the second most utilised imaging technique. It does not expose the patient or operator to ionising radiation and there is minimal preparation required making it a quick and efficient diagnostic tool. It is, however, operator dependent and time should be taken to develop an understanding of the procedures to ensure a positive outcome for the patient.

  Sound waves

  Sound is a wave, which moves longitudinally. It is created by vibrating objects and moves via particle interaction from one location to another. Each particle pushes on its neighbouring particle and moves it in a forward direction. It then returns to its original position at the end of the interaction. This backward and forward movement is parallel to the direction of movement of the wave. In some areas of the wave, the particles are compressed together (compressions) and other areas the particles are spread apart (rarefactions).

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  eBook - ePub

  Ultrasound and Infertility

  • Asim Kurjak(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 1

  BASIC PHYSICS OF ULTRASOUND

  Branko Breyer

  TABLE OF CONTENTS

  I.        Introduction II.       Physical Principles A.    Ultrasound Waves B.    Ultrasound Propagation in Tissues 1.    Refraction and Reflection of Ultrasound Waves III.      Echoscopic Systems A.    Main Blocks of an Echoscope B.    Transducer and the Ultrasound Beam C.    Echoscope Probes and Scanning Systems D.    Attenuation Compensation: TGC E.    Dynamic Range F.    Some Notes on Resolution and Practical Use G.    Looking at the Image, Artifacts IV.      Doppler Effect and Its Use V.       Some Practical Advice References

  I. INTRODUCTION

  In this chapter, we describe the basic physical and technological principles of ultrasound diagnostics without mathematical treatment, except for some simple formulas, yet include comments relevant for practical use. Ultrasound diagnostic instruments and procedures are still in fast development, so that mere knowledge of manipulation with the existing instruments is definitely insufficient for sound usage of the existing instruments to come in a few years. The knowledge of underlying principles allows one to understand what is actually new in an instrument, and what are the supposed advantages.

  II. PHYSICAL PRINCIPLES

  A. Ultrasound Waves

  Ultrasound is, per definition, the sound of a frequency higher than the hearing limit of the human ear, i.e., above 16 to 20 kHz. Bat’s definition of ultrasound would be different. In medical diagnostics, one normally uses ultrasound waves of frequencies between 2 and 10 MHz. Basic physical principles are equally valid for audible sound as for ultrasound, only at different scales. Ultrasound is a mechanical wave, i.e., it consists of mechanical vibrations of medium particles through which it propagates. In soft tissues, the medium particles vibrate along the direction of wave propagation creating their densifications and rarefactions in space. Such a wave is called a longitudinal wave. The particles (molecules) oscillate around their (stochastic) balance positions with no net flow of matter, however, the energy flows. At very high energy densities some net flow can be induced, but this does not apply to energies of ultrasound used in diagnostics. Other types of waves like transversal and Raileigh cannot propagate to any appreciable distance in soft tissues. Ultrasound waves are characterized by parameters like frequency, wavelength, propagation speed, intensity, and pressure. Frequency is expressed in hertz (Hz), i.e., cycles per second. The physical dimension is 1/s; 1 Hz = 1 c/s, 1 kHz = 1000 c/s, and 1 MHz = 1 million c/s. The frequency used in diagnostics largely influences their properties. Wavelength is the distance between the same phases of compression of the medium in two consecutive cycles in space and is measured in meters or its subunits like millimeters. The propagation speed depends mainly on the media (tissue) properties through which the wave propagates and is related with frequency and wavelength as follows:

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  eBook - ePub

  Introduction to Medical Physics

  • Stephen Keevil, Renato Padovani, Slavik Tabakov, Tony Greener, Cornelius Lewis, Stephen Keevil, Renato Padovani, Slavik Tabakov, Tony Greener, Cornelius Lewis(Authors)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  The physical principles of the interaction between ultrasound and body tissues are the basis of this constant flourishing of new techniques, but they are not enough to account for all of them. In fact, modern computing methods such as neural networks are playing an ever-growing role in ultrasound and can add new knowledge of the human body sometimes even before the underlying detailed phenomena are well understood. So, we can be sure that the coming years will bring us new interesting and amazing advances. Medical physicists must play an active part in that process and can contribute to assessment of which proposed technical advances are truly clinically beneficial.

  Further Reading

  1. Baker, K. G., Valma J.Robertson, Francis A.Duck 2001 A review of therapeutic ultrasound: Biophysical effects.Physical Therapy 81.7: 1351–1358.
  2. Bercoff, J. 2011, Aug 23 Ultrafast ultrasound imaging. Ultrasound Imaging-Medical Applications . 3–24.
  3. Bercoff, J., M. Tanter, M. Fink 2004 Supersonic shear imaging: A new technique for soft tissue elasticity mapping.IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 51.4: 396–409.
  4. Beyer, R. T. 1974 Nonlinear acoustics . Monterey: Department of the Navy.
  5. Church, Charles C. 2007 A proposal to clarify the relationship between the thermal index and the corresponding risk to the patient.Ultrasound in Medicine & Biology 33.9: 1489–1494.
  6. Cleveland, R. O., James A. McAteer 2007 The physics of shock wave lithotripsy.Smith’s Textbook on Endourology 1529–558.
  7. Dai, J. C., et al . 2019 Innovations in ultrasound technology in the management of kidney stones.Urologic Clinics 46.2: 273–285.
  8. J. Ultrasound Med
     2000- Section 7—Discussion of the mechanical index and other exposure parameters.Journal of Ultrasound Medicine 19.2: 143–168.
  9. Jenne, J. W., Tobias Preusser, Matthias Günther 2012 High-intensity focused ultrasound: Principles, therapy guidance, simulations and applications.Zeitschrift für Medizinische Physik 22.4: 311–322.
  10. Jensen, J. A. 2006 Medical ultrasound imaging.Progress in Biophysics and Molecular Biology 93.1–3: 153–165.
  11. Lingeman, J. E., et al.

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