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Ultrasonic echolocation has its origins in the military and industrial contexts. We describe in this chapter the more important of the early attempts to adapt the technology for medical purposes.1 We investigate the problems and difficulties—biological, physical, electronic, social, and organizational— that confronted the pioneers of diagnostic ultrasound, and outline the modality ’s state of development before Tom Brown and Ian Donald entered the field. Particular attention is given to Douglass Howry in Denver and John Wild in Minneapolis, since study of their work reveals instructive similarities to and differences from the approach taken by Brown. The ears of a healthy young human can detect sound over a range of frequencies , from about 30Hz to about 20kHz. Thus, by convention, sound of frequency greater than 20kHz is termed ultrasound. The medical ultrasound scanner works by echolocation. Echolocation technologies (sonar and radar are other examples) transmit pulses of energy from known positions and in known directions and detect returning echoes.2 In the case of diagnostic ultrasound , a pulse of high-frequency sound is sent into the body. Some of that sound energy is reflected back from the body’s internal surfaces, and the time taken for the echoes to return to the transmitter is measured. If the speed of sound in tissue is known, the distance between the transmitter and the surface that produced the echo can be determined. From these basic pieces of information (position of source, direction, and distance), an image of the interior of the body can be built up.3 Ultrasound pulses are generated and received by a transducer with a piezoelectric element.4 In obstetrics and gynecology, frequencies of 3 to 10MHz are typically used. With such high frequencies, the pulses can be very short and confined to a small-diameter beam, thereby producing images that reveal fine detail.5 There is a practical upper limit to the frequency that can be employed, Chapter Two Diagnostic Ultrasound before Thomas Brown Diagnostic Ultrasound before Thomas Brown 13 however, as the absorption of sound energy increases with frequency and hence the depth of effective penetration into tissue is reduced. The scientific study of sound beyond the range of human hearing began toward the end of the nineteenth century. In his classic text The Theory of Sound, published in 1877, Lord Rayleigh developed mathematical characterizations of a wide range of acoustical phenomena, including the relationships between frequency and reflection, diffraction, and absorption.6 In April 1912, shortly after the sinking of the Titanic, Lewis Fry Richardson, a British applied mathematician, patented a method of locating icebergs at sea by sending out pulses of sound and detecting the incoming echoes.7 However, Richardson was unable to secure a commercial sponsor to allow him to develop his ideas. He worked on the project intermittently for many years, but his invention was never deployed. Just before the outbreak of the First World War, his friend Maurice Wilson advised him to approach the Admiralty: “It would be extraordinarily useful to the country just now for our fleet to be able to detect the presence of other boats and particularly submarines.” But Wilson added, “Perhaps you feel you would not like to lend your aid to the method of warfare.”8 He was right on both counts. A Quaker and a pacifist, Richardson refused to be involved in any research that had a direct military application. For the next forty years, however, the development of ultrasonic echolocation would be intimately linked with military research and deployment. In the second decade of the twentieth century, the imminent prospect of war stimulated the navies of Western Europe and the United States to explore methods of protecting ships from the increasing threat of the submarine. In 1915, Constantin Chilowsky, a Russian engineer living in Switzerland, suggested that echolocation could be an effective method of detection, if a sound signal of sufficiently high frequency were used. Chilowsky’s idea was quickly taken up by the French physicist Paul Langevin.9 By 1916, Chilowsky and Langevin , working together and in cooperation with the French Navy, had demonstrated that it was possible to detect submerged objects by using ultrasound beams of about 40kHz.10 Two serious problems remained to be solved, however , before an ultrasonic antisubmarine system could be put into military service . First, ultrasound had to be generated at an intensity that would permit echolocation over operationally useful distances. Second, a reliable means had to be found for recognizing the relatively weak returning echo. Langevin ingeniously...

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