The History of Ultrasound: Part 4

The History of Ultrasound: Part 4

A-mode (amplitude-mode) US represents a one-dimensional characterization of a reflected sound wave that uses a pulse-echo technique to determine the depth and dimen­sions of an organ.


Echo amplitude is plotted on the vertical axis, and the time needed for the echo to return is plotted on the horizontal axis.


Limitations of this method include the inability to determine direction or the shape of an object from which the echo originated.

a vs b

This mode has been made relatively obsolete by B-mode US; however, A-mode US is still used today in ophthalmology to measure the orbital length and assess for intra­ocular masses.

George D. Ludwig, was the first to convert A-mode US imaging, which had been used to detect minute flaws in metal, into medical applications. His initial research focused on the physical characteristics of ultrasound in various tissues, identifying the acoustic impedance of fat, muscle, and various types of gallstones.


And here it is, the infographic:

Full (and very interesting) article at:

Kaproth-Joslin et al. The History of US: From Bats and Boats to the Bedside and Beyond. Radiographics. Vol 35. May-June 2015: 960-70

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Want to read the last part? The History of US: Part 5 is [here]

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