Recent Advances in Ultrasonic Imaging
Ultrasonics has been used for many years to detect flaws in materials by means of a pulse echo or A-scan technique. Ultrasonic images are formed by displaying the echoes in a two dimensional pattern so that t he spatial relationships between the interfaces and acoustic impedance discontinuities t hat give rise to the echoes are maintained. When the echo data is arranged in this way, it is possible for one's eye and brain to serve as a very sophisticated pattern recognition system to detect flaws or defects within an object. This capability is particularly important when one is examining an object that normally has a considerable amount of internal structure. Since most of my experience is with medical applications, I will take the human abdominal region as an example. An ultrasonic image will be able to delineate the more or less known outlines of these normal internal structures. Frequently, however, the purpose of such an examination is to look for some abnormality such as a tumor or cyst and using an ultrasonic image these structures can be differentiated from the normal structures by those who have been trained in this sort of procedure. This can be done because the operator has learned to recognize certain patterns and he is able to employ his eye-brain pattern recognition system when the echo data is presented in the form of an image.