Threshold Contrast for Three Real-Time Acoustic-Imaging Systems

Abstract

Three approaches to real-time acoustic imaging are presently being worked on in various laboratories. These approaches involve the use of static-ripple diffraction, dynamic-ripple diffraction and Bragg diffraction. Experimental results indicate that good images can be obtained from each and that the systems currently appear to be quite competitive. This paper compares the ultimate potential performance of systems of each of the three types in terms of threshold contrast and sensitivity. The comparisons not only give an indication of the inherent capabilities and limitations of the systems but also of how far the present systems are from achieving ideal behavior.

The analysis is based on idealized models of each type and also of a non-existing, hypothetical system with highly desirable theoretical characteristics. This latter system would be difficult to build as a practical instrument but is useful in analyses since it can serve as a theoretical standard of excellence against which to measure the performance of the other systems.

The systems are shown to vary in different ways with various parameters such as acoustic frequency of operation, resolution-cell area and power in the laser beam from which the optical image is eventually derived. However, for a set of consistent operating conditions selected to be compatible with the application of medical diagnosis, a sample calculation shows that the calculated capabilities of the three systems are of the same order. Thus the decision of employing one particular system in preference to another in this application would have to be based on practical considerations and a knowledge of how close the system comes to achieving the ideal performance calculated.