Improved ultrasonic image generation through tomographic image fusion

Techniques for the generation of quantitative ultrasonic images in non-destructive testing have generally involved a substantial cost in terms of data storage and computational time, and thus have found limited application. Preference has therefore been given to the more straightforward imaging methods, such as main beam projection, that detect the presence of defects and provide a limited flaw sizing capability. The relatively small number of flaws requiring detailed examination, coupled with substantial increases in available data storage and computational power, has made it possible to use a number of straightforward tomographic reconstruction methods to produce images of flaws contained within the material under examination. These can then be fused together into a single image from which more accurate measurements of flaw size, shape and orientation can be made. The three tomographic methods that have been implemented in this work are reflection tomography, time-of-flight diffraction tomography and transmission tomography. Selection of images used in the fusion process depends on the nature of the flaw, as each of these methods identifies different characteristics of the flaw shape. The reconstruction methods have been used to generate images from a variety of flaws contained within aluminum cylinders, some or all of the images being fused to produce the final flaw image. Time domain measurements used in the reconstruction were then applied to simulate the application of multi-element arrays for data acquisition and the subsequent tomographic images evaluated. (C) 1999 Published by Elsevier Science B.V. All rights reserved.