First experiments on high-frequency sounds can be traced back to the 18th century when the Italian priest, natural scientist and pioneer of physiology, Lazzaro Spallanzani (1729-1799) demonstrated the ability of bats to navigate accurately in the dark through the echo-reflection of inaudible high-frequency sounds.
In 1826, the Swiss physicist Jean-Daniel Colladon (1802-1893) used an underwater bell to successfully determine the speed of sound in the water of Lake Geneva. In his famous treatise The Theory of Sound published in 1877, John William Strutt, 3rd Baron Rayleigh (1842-1919), defined the sound wave as a mathematical equation and thus set the basis for future practical work in acoustics.
The breakthrough in the evolution of high frequency echo-sounding technology was presented in the experiments of the brothers Pierre (1859-1906) and Jacques Curie (1855-1941) in Paris. They found out that an electric potential was produced when mechanical pressure was exerted on a quartz crystal. Further research and development in piezoelectricity soon followed.
In 1912, Alexander Belm (1880-1942) of Vienna was credited for his description of an underwater echo-sounding device. Underwater sonar detection systems were developed for the purpose of underwater navigation by submarines in World War I. Research and development of naval and military radar were enhanced during World War II.
In the 1940s, high-intensity ultrasound technology systematically started to enter the realm of medicine. Initially applied mainly in therapy, ultrasound technology was also subject to numerous experiments for diagnostic use. The treatise Der Ultraschall in der Medizin (“Ultrasound in Medicine”) published by H. Gohr and T. Wedekind from the Medical School of Cologne, Germany, in 1940, suggested echo-reflection methods to detect tumours, exudates or abscesses. However, the paper lacked scientific results from experiments. The Viennese neurologist Karl Theo Dussik (1908-1968) began his experiments on ultrasound in the late 1930s. He is among the first physicians to have employed ultrasound in medical diagnosis.
The first urological applications referred to ultrasonic scans of the kidneys. The so-called “Pan-scanner” with the transducer rotating in a semicircular arc around the patient was introduced in 1957. The patient sat on a modified dental chair strapped against the plastic window of a semicircular pan filled with saline solution, while the transducer rotated through the solution in the semicircular arc.
In the late 1950s the first “B-mode” scanner replaced the unidirectional “A-mode” ultrasound technique. This technology is still in use today.
Research and development swiftly continued throughout the second half of the 20th century. In the early 1980s it became clear that mechanical sector scanners, either rotating, oscillating or wobbling, produced better images than electronic linear-array scanners. The era of digitalization started in the 1990s and led to a powerful enhancement in image quality and resolution.
Ultrasonography remains an important tool in endourology today.