Sound beyond hearing
Ultrasound means sound with a frequency above what people can hear, and diagnostic ultrasound uses frequencies far higher than that, usually in the megahertz range. The basic method is pulse-echo. A small transducer sends a brief burst of sound into the body, and when the sound meets a boundary between tissues, part of it reflects back. The time it takes to return indicates how deep the boundary is, and the strength of the echo gives a rough measure of the boundary.
From the Curies to sonar
The physical groundwork came from the discovery of piezoelectricity by Pierre and Jacques Curie in 1880: certain crystals produce a voltage when squeezed, and deform when a voltage is applied. That property allows one crystal to both send and receive sound. During the First World War, Paul Langevin in France, working with others, used quartz transducers to send ultrasonic pulses through water and detect submarines. That work was a foundation for sonar, and it led to industrial uses such as finding flaws in metal castings, which Sokolov and later Floyd Firestone and others developed in the 1930s and 1940s.
Early medical attempts
Medicine’s first interest was not imaging but treatment and measurement. The Austrian neurologist Karl Dussik and his brother Friedrich published a 1942 paper describing transmission of ultrasound through the head in an attempt to show brain ventricles. Later examination suggested that the shadows they saw may have been artifacts of the skull, but the effort helped inspire others.
After the Second World War, researchers in several countries used surplus radar and sonar equipment. In the United States, Douglass Howry and Joseph Holmes in Colorado and Minnesota built scanners in which the patient sat in a water bath and a transducer moved around, producing cross-sectional views. George Ludwig, a Navy researcher, studied the speed of sound in tissue and the detection of gallstones. In Japan, Toshio Wagai, Kenji Tanaka and others explored similar uses.
The heart and the womb
Two applications stood out in the 1950s. In Lund, Sweden, the cardiologist Inge Edler and the physicist Hellmuth Hertz borrowed an industrial ultrasonic flaw detector in 1953 and recorded moving heart structures, creating echocardiography.
In Glasgow, the obstetrician Ian Donald, engineer Tom Brown and colleague John MacVicar developed a scanner in the mid-1950s, also starting from industrial flaw-detection equipment. In 1958 they published a paper in The Lancet describing the use of ultrasound to examine abdominal masses and to study pregnancy. The device displayed brightness-modulated cross-sections, now called B-mode images. Their work helped establish ultrasound as a practical obstetric tool, and over the following years scanners were refined for measuring the fetus and locating the placenta.
Making it practical
Early scanners were large and slow, building a picture over many seconds. Through the 1960s and 1970s, mechanical scanning heads and later transducer arrays allowed images to update many times per second, so doctors could watch movement as it happened. Gray-scale images, which show more than bright and dark, arrived in the 1970s thanks to better electronics. Doppler techniques, based on the change in frequency of echoes from moving blood, added the ability to measure blood flow. Digital processing, small probes and portable machines followed in later decades, and some devices are now small enough to be held in one hand, powered by silicon chips.
Why it spread
Ultrasound did not involve ionizing radiation, equipment was cheaper than CT or MRI and far lighter than large X-ray machines, and the scanner could be moved to the patient’s bedside. Those practical advantages made it common in obstetrics, cardiology and abdominal examinations. Its limits include difficulty imaging through bone or gas, and image quality that depends heavily on the operator’s skill. Historians also note that the long-term safety of widespread use was studied over time, and professional bodies have issued guidance on its responsible use.
This article is history, not medical advice.