Developments of Ultrasonic Measurement Technology for Acoustic Imaging

The developments of acoustic imaging technology depend on those of ultrasonic measurement technology. The history of ultrasonic measurement can be said to have started from the Titanic disaster in 1912, which motivated engineers to prevent such a tragedy from happening again. The pulse-echo method was cultivated in the ultrasonic field using Fessenden’s oscillator to measure the distance between the ship and icebergs, 1In the ultrasonic measurements, an important field of nondestructive testing (NDT) of materials and components of structures has been developed mainly by the pulse-echo method. In the early 1940’s, the pulse-echo method of A-scan was developed for flaw- detecting equipments in the industry, such as in ship building companies during the World War II by Firestone and Fredricks.2 Two -dimensional images known as B-scan and C-scan images were developed by the introduction of scanning techniques of an ultrasonic beam into the pulse-echo measurement system, which made it possible to image the position and shape of flaws in the components on the screen of CRT display.3 Figure 1 shows the principle of scanning for imaging. In the medical community, the cross-sectional patterns of B-scan images are called “B-mode images” or “ultrasono-tomograms”.4