Diagnostic Ultrasound Imaging: Inside Out

Thomas L. Szabo

• Publisher: Academic Press
• Year: 2004
• ISBN:
  9780080491134
• Topic: Biological Sciences
• Subtopic: Biotechnology
• Index: Biological Sciences

Diagnostic Ultrasound Imaging provides a comprehensive introduction to and a state-of-the-art review of the essential science and signal processing principles of diagnostic ultrasound. The progressive organization of the material serves beginners in medical ultrasound science and graduate students as well as design engineers, medical physicists, researchers, clinical collaborators, and the curious. This it the most comprehensive and extensive work available on the core science and workings of advanced digital imaging systems, exploring the subject in a unified, consistent and interrelated manner. From its antecedents to the modern day use and prospects for the future, this it the most up-to-date text on the subject. Diagnostic Ultrasound Imaging provides in-depth overviews on the following major aspects of diagnostic ultrasound: absorption in tissues; acoustical and electrical measurements; beamforming, focusing, and imaging; bioeffects and ultrasound safety; digital imaging systems and terminology; Doppler and Doppler imaging; nonlinear propagation, beams and harmonic imaging; scattering and propagation through realistic tissues; and tissue characterization.

• Based on the author's over thirty-five years of experience in developing laboratory methodology and standards and conducting research in ultrasound.
• Conveys the fundamentals of diagnostic ultrasound as well as state-of-the-art reviews of major topics from a historical perspective. Matlab MATLAB problems and examples included.
• MATLAB problems and examples included

1

INTRODUCTION

Chapter Contents

1.1 Introduction

1.1.1 Early Beginnings

1.1.2 Sonar

1.2 Echo Ranging of the Body

1.3 Ultrasound Portrait Photographers

1.4 Ultrasound Cinematographers

1.5 Modern Ultrasound Imaging Developments

1.6 Enabling Technologies for Ultrasound Imaging

1.7 Ultrasound Imaging Safety

1.8 Ultrasound and other Diagnostic Imaging Modalities

1.8.1 Imaging Modalities Compared

1.8.2 Ultrasound

1.8.3 X-rays

1.8.4 Computed Tomography Imaging

1.8.5 Magnetic Resonance Imaging

1.9 Conclusion

Bibliography

References

1.1 INTRODUCTION

The archetypal modern comic book superhero, Superman, has two superpowers of interest: x-ray vision (the ability to see into objects) and telescopic vision (the ability to see distant objects). Ordinary people now have these powers as well because of medical ultrasound imaging and sonar (sound navigation and ranging) instruments. Ultrasound, a type of sound we cannot hear, has enabled us to see a world otherwise invisible to us.

The purpose of this chapter is to explore medical ultrasound from its antecedents and beginnings, relate it to sonar, describe the struggles and discoveries necessary for its development, and provide the basic principles and reasons for its success. The development of medical ultrasound was a great international effort involving thousands of people during the last half of the twentieth century, so it is not possible to include many of the outstanding contributors in the short space that follows. Only the fundamentals of medical ultrasound and representative snapshots of key turning points are given here, but additional references are provided. In addition, the critical relationship between the growth of the science of medical ultrasound and key enabling technologies is examined. Why these allied technologies will continue to shape the future of ultrasound is also described. Finally, the unique role of ultrasound imaging is compared to other diagnostic imaging modalities.

1.1.1 Early Beginnings

Robert Hooke (1635–1703), the eminent English scientist responsible for the theory of elasticity, pocket watches, compound microscopy, and the discovery of cells and fossils, foresaw the use of sound for diagnosis when he wrote (Tyndall, 1875):

It may be possible to discover the motions of the internal parts of bodies, whether animal, vegetable, or mineral, by the sound they make; that one may discover the works performed in the several offices and shops of a man’s body, and therby (sic) discover what instrument or engine is out of order, what works are going on at several times, and lie still at others, and the like. I could proceed further, but methinks I can hardly forbear to blush when I consider how the most part of men will look upon this: but, yet again, I have this encouragement, not to think all these things utterly impossible

Many animals in the natural world, such as bats and dolphins, use echo-location, which is the key principle of diagnostic ultrasound imaging. The connection between echo-location and the medical application of sound, however, was not made until the science of underwater exploration matured. Echo-location is the use of reflections of sound to locate objects.

Humans have been fascinated with what lies below the murky depths of water for thousands of years. “To sound” means to measure the depth of water at sea, according to a naval terms dictionary. The ancient Greeks probed the depths of seas with a “sounding machine,” which was a long rope knotted at regular intervals with a lead weight on the end. American naturalist and philosopher Henry David Thoreau measured the depth profiles of Walden Pond near Concord, Mass., with this kind of device. Recalling his boat experiences as a young man, American author and humorist Samuel Clemens chose his pseudonym, Mark Twain, from the second mark or knot on a sounding lead line. While sound may or may not have been involved in a sounding machine, except for the thud of a weight hitting the sea bottom, the words “to sound” set the stage for the later use of actual sound for the same purpose.

The sounding-machine method was in continuous use for thousands of years until it was replaced by ultrasound echo-ranging equipment in the twentieth century. Harold Edgerton (1986), famous for his invention of stroboscopic photography, related how his friend, Jacques-Yves Cousteau, and his crew found an ancient Greek lead sounder (250 B.C.) on the floor of the Mediterranean sea by using sound waves from a side scan sonar. After his many contributions to the field, Edgerton used sonar and stroboscopic imaging to search for the Loch Ness monster (Rines et al., 1976).

1.1.2 Sonar

The beginnings of sonar and ultrasound for medical imaging can be traced to the sinking of the Titanic. Within a month of the Titanic tragedy, British scientist L. F. Richardson (1913) filed patents to detect icebergs with underwater echo ranging. In 1913, there were no practical ways of implementing his ideas. However, the discovery of piezoelectricity (the property by which electrical charge is created by the mechanical deformation of a crystal) by the Curie brothers in 1880 and the invention of the triode amplifier tube by Lee De Forest in 1907 set the stage for further advances in pulse-echo range measurement. The Curie brothers also showed that the reverse piezoelectric effect (voltages applied to certain crystals cause them to deform) could be used to transform piezoelectric materials into resonating transducers. By the end of World War I, C. Chilowsky and P. Langevin (Biquard, 1972), a student of Pierre Curie, took advantage of the enabling technologies of piezoelectricity for transducers and vacuum tube amplifiers to realize practical echo ranging in water. Their high-power echo-ranging systems were used to detect submarines. During transmissions, they observed schools of dead fish that floated to the water surface. This shows that scientists were aware of the potential for ultrasound-induced bioeffects from the early days of ultrasound research (O’Brien, 1998).

The recognition that ultrasound could cause bioeffects began an intense period of experimentation and hopefulness. After World War I, researchers began to determine the conditions under which ultrasound was safe. They then applied ultrasound to therapy, surgery, and cancer treatment. The field of therapeutic ultrasound began and grew erratically until its present revival in the forms of lithotripsy (ultrasound applied to the breaking of kidney and gallstones) and high-intensity focused ultrasound (HIFU) for surgery. However, this branch of medical ultrasound, which is concerned mainly with ultrasound transmission, is distinct from the development of diagnostic applications, which is the focus of this chapter.

During World War II, pulse-echo ranging applied to electromagnetic waves became radar (radio detection and ranging). Important radar contributions included a sweeping of the pulse-echo direction in a 360-degree pattern and the circular display of target echoes on a plan position indicator (PPI) cathode-ray tube screen. Radar developments hastened the evolution of single-direction underwater ultrasound ranging devices into sonar with similar PPI-style displays.

1.2 ECHO RANGING OF THE BODY

After World War II, with sonar and radar as models, a few medical practitioners saw the possibilities of using pulse-echo techniques to probe the human body for medical purposes. In terms of ultrasound in those days, the body was vast and uncharted. In the same way that practical underwater echo ranging had to wait until the key enabling technologies were available, the application of echo ranging to the body had to wait for the right equipment. A lack of suitable devices for these applications inspired workers to do amazing things with surplus war equipment and to adapt other echo-ranging instruments.

Fortunately, the timing was right in this case because F. Firestone’s (1945) invention of the supersonic reflectoscope in 1940 applied the pulse-echo ranging principle to the location of defects in metals in the form of a reasonably compact instrument. A diagram of a basic echo-ranging system of this type is shown in Figure 1...