DIVISION OF INSTRUMENTATION: FORMATION OF IMAGES BY ULTRASONIC RAYS*

Abstract

Medical Ceiztev Bvoolzly?z, ATezv Yovk, AT, Y .Methods presently employed by researchers in the field of ultrasound in an attempt to produce sonic images of high resolution involve one or the other of two systems for handling the sonic energy. These a r e the echo timing technique and the sonic image technique, The first uses the principles of sonar, where the sonic energy reflected from an acoustically discontinuous interface is analyzed for travel time and per cent absorption, The second system has the subject broadly illuminated by a transmitting transducer whereafter the sonic energy that has passed either through or from the subject, is collected by an image-forming sonic lens. Transduction of the sonic image into a visible one is then carried out.Various methods exist for transducing sonic images into visible ones. Ernst (1945) and Ernst & Hoffman (1952) have reviewed chemical methods of doing so. Sokolov (1949) published a description of an ultrasonic microscope in which a sophisticated electronic system was used, The system depends on the fact that mechanical vibrations do not spread over a damped crystal face, so that a crystal generates a piezo-electric image in response to a pattern of ultrasonic excitation. One of the present authors (Suckling 1956) has investigated this phenomenon under various conditions. These studies revealed that for normally incident radiation a shadow edge of piezo-electric response in which intensity drops to a little less than half in a distance of a millimeter is possible when using a 3-megacycle resonant quartz plate.In developing electronic methods of converting piezo-electric patterns to visible images it is possible to use a number of different approaches, One system has involved mounting a quartz crystal as part of the face of an oscilloscope tube. The electron beam is made to sweep the back of the crystal face, and provision is made to collect all secondary electrons. The energy of these electrons is ,found to be modulated by the piezo-electric voltage of the surface from which they originated. The method first used by Sokolov in 1949 has since been used by Jacobs (1965) and other workers. Smyth and Sayers (1959) have set up a slightly different but also electronic system. The present author built a demountable oscilloscope and tried out Sokolov's method of image transduction in 1954, but decided that it was too insensitive for his purposes. A mechanical capacitative crystal face scanning system seemed to offer better sensitivity although, of course, far less in ultimate convenience. Using various mechanical crystal face scanners, it has been possible to demonstrate a number of phases of ultrasonic-optics. Diffraction patterns, Newton's rings in sound, and various shadowgraphs and images have been clearly shown. Oscilloscopic reproductions of images of wire test patterns and of other opaque objects have been photographed with