Chapter 1 Doppler Sonography: A Brief History Dev Maulik The origins of modern medical technology may be appears, however, that Doppler never used his second traced to nineteenth-century europe, when the indus- name. trial revolution ushered in sweeping changes in every Doppler's father, a master stone mason, was a man aspect of life. Of all the momentous discoveries and in- of wealth and fame. Because of frail health Doppler ventions of this period, there was one relatively obscure was sent to school instead of joining the family trade. scientific event that laid the foundation for the subse- In 1822 Johann Doppler requested that Simon Stamp- quent development of Doppler technologies in the fer, a professor at the local Lyceum, evaluate his son's twentieth century ± the discovery of a natural phenom- aptitude. Stampfer was impressed with young Chris- enon that came to be known as the Doppler effect. An- tian's scholastic abilities in mathematics and science, other critical event was the discovery of the piezoelec- tric phenomenon by Pierre Curie and Jacques Curie, which enabled the development of ultrasonic transdu- cers many decades later. This chapter briefly describes the origin of the Doppler theory during the nineteenth century and traces the development of diagnostic Dop- pler ultrasound technology during the second half of the twentieth century to the present. Christian Andreas Doppler and the Doppler Theory The Doppler effect is defined as the observed changes in the frequency of transmitted waves when relative motion exists between the source of the wave and an observer. The frequency increases when the source and the observer move closer and decreases when they move apart. The phenomenon bears the name of its discoverer, Christian Andreas Doppler, an Austrian mathematician and physicist (Fig. 1.1), born to Jo- hann Evangialist and Therese Doppler on November 29, 1803 in Salzburg, Austria. The house in which he was born and raised still stands across the square from the family home of Wolfgang Amadeus Mozart in the Markart Platz. For nearly a century Doppler's Christian name has been consistently misquoted in the literature as Johann Christian. Doppler was bap- tized on the day of his birth at the Church of St. An- dra, which was originally in close proximity of the Doppler home. Eden [1] conducted a thorough search for Doppler's birth and baptismal records and found Fig. 1.1. Christian Andreas Doppler. The oil painting was them still preserved in the Church of St. Andra, done by an unidentified artist probably at the time of Doppler's marriage in 1836. The original is in the Austrian which had moved to a new location in Salzburg in Academy of Sciences to whom it was donated by Mathilda 1898. These documents conclusively established that von Flugl, the great granddaughter of Christian Doppler. Doppler had been christened Christian Andreas. It (Reprinted from [1], with permission) 2 D. Maulik Fig. 1.2. Title page of Christian Doppler's paper titled ªOn the Coloured Light of the Double Stars and Certain Other Stars of the Heavens.º (Reprinted from [1], with permission) and at his recommendation Doppler was sent to the Society of Sciences in Prague. Ironically, there were Polytechnic Institute of Vienna for further education. only five people and a transcriber in the audience. Doppler studied mathematics and physics in Vien- The paper was entitled ªOn the Colored Light of the na for 3 years and then returned to Salzburg where Double Stars and Certain Other Stars of the Heavensº he concluded his education and eventually graduated (Fig. 1.2) and was published in 1843 in the Proceed- in 1829. For 4 years he held the position of assistant ings of the society [2]. Of 51 papers Doppler pub- in higher mathematics at the Vienna Polytechnic In- lished, this one was destined to bring him lasting rec- stitute. Following this assitantship he experienced dif- ognition. ficulty finding an appropriate position, and in 1835 Doppler's work was based on the theory of the aber- he seriously considered emigrating to the United ration of light developed by Edmund Bradley, the eigh- States. At this point, however, he was offered and ac- teenth-century British Astronomer Royal. Doppler es- cepted the position of Professor of Elementary Mathe- tablished the principle of frequency shift and devel- matics and Commercial Accounting at the State Sec- oped the formula for calculating the velocity from the ondary School in Prague. The following year he was shift. For elucidating the theoretic background of the also appointed Supplementary Professor of Higher principle, Doppler used various analogies and exam- Mathematics at the Technical Institute in Prague. In ples primarily based on transmission of light and 1841 Christian Doppler became a full Professor of sound. Although his examples of sound transmission Mathematics and Practical Geometry at the latter in- were correct, those involving light transmission were stitution. One year later, on May 25, he presented his erroneous, as he presumed that all stars emitted only landmark paper on the Doppler effect at a meeting of pure white light. He postulated that the color of a star the Natural Sciences Section of the Royal Bohemian was caused by the relative motions of the star and the a Chapter 1 Doppler Sonography: A Brief History 3 earth causing apparent spectral shifts of the emitted white light. The spectrum would shift toward blue if the star approached the earth; conversely, the spectrum would shift to red if the star receded away from the earth. When describing these phenomena Doppler did not take into account preexisting research on light transmission and spectrum. Herschel [3] had already discovered infrared radiation, and Ritter [4] had de- scribed ultraviolet radiation; but it appears that Dop- pler was unaware of these important developments. Verification of Doppler's Theory As was to be expected, the paper generated critical responses. The most significant challenge came from a young Dutch scientist working at the University of Utrecht in Holland, Christoph Hendrik Diederik Buys Ballot (Fig. 1.3). In 1844 Buys Ballot proposed to re- fute the Doppler theory by designing an experiment involving sound transmission as his doctoral research project. Conveniently for him, a new railroad had just been established between Amsterdam and Utrecht, and the Dutch government gave him permission to use this railway system to verify the Doppler effect on sound transmission (Fig. 1.4). The first experi- ment was designed in February 1845. Two horn players who apparently had perfect pitch were chosen to participate in the experiment. The calibration was accomplished by one musician blowing a note and Fig. 1.3. C.H.D. Buys Ballot (1817±1890). (From [40], with the other identifying the pitch of the tone. After this permission) calibration was performed, one player was positioned on the train, and the other stood along the track. As the train passed, the stationary musician on the fute the Doppler theory ultimately confirmed it. Buys trackside perceived that the note blown by the musi- Ballot proved not only the existence of the Doppler cian on the train was half a note higher when the effect in relation to sound transmission but its angle train approached him and half a note lower when it dependency as well. Incredibly, Buys Ballot still re- moved away. Unfortunately, a raging blizzard forced fused to accept the validity of the theory for the pro- Buys Ballot to abandon his experiment and to resche- pagation of light and most of the scientific commu- dule it in a more temperate season. The results from nity of the nineteenth century did not acknowledge the first experiment were published within less than a the validity of Doppler's theory because of his erro- month in a music journal [5]. neous interpretation of astronomical phenomena. Buys Ballot conducted the experiment again in As translated by Eden [1], Doppler's response was early June of the same year [6]. Three teams were sta- impressive in its foresight: ªI still hold the trust ± in- tioned along the track. Each team was composed of a deed, stronger than ever before ± that in the course horn player, an observer, and a manager. A fourth of time, this theory will serve astronomers as a wel- team was on a flat car behind the locomotive. Buys come help to probe the happenings of the universe, at Ballot positioned himself on the foot plate next to the times when they feel deserted by all other methodsº engineer. This experiment was more sophisticated, [7]. This statement was prophetic. Since the begin- but it also encountered environmental complications ning of the twentieth century, the Doppler principle as the summer heat seriously interfered with the cor- has been used extensively not only in astronomy but rect tuning of the musical instruments. The musi- also in the immensely diverse fields of science and cians originally tried to use one-sixteenth of a single technology. note but failed, and the final experiment was done in Doppler lived only 10 years after publishing his eights. The results were remarkable despite all the paper on the frequency shift; however, these few years trials and tribulations. The study that set out to re- brought him well-deserved recognition and honor. He 4 D. Maulik Fig. 1.4. Model of the locomo- tive (named Hercules) used in the first experiments. (From [40], with permission) was elected to the membership of the Royal Bohe- gradually emerged. The first sonar equipment for de- mian Society of Sciences in 1843 and of the highly tecting submarines was developed by Paul Langevin prestigious Imperial Academy of Sciences in Vienna of France, who also pioneered the use of piezoelectric in 1847.