Area Function Imaging in Two-Dimensional Ultrasonic Computerized Tomography
In ultrasonic nondestructive evaluation (NDE) studies, impulse response is often used to evaluate internal defects. Under the far-field Born approximation , the impulse response can be written as the product of the second derivative of the area function with respect to the coordinate along the line-of-sight and a scattering constant which depends on the material properties as well as scattering directions . The line-of-sight is a straight line along the illumination direction for pulse-echo tests, and the area function is an artificial time domain waveform equal to the target cross-sectional area intersected by an imaginary transverse plane travelling along the line-of-sight. Hence the double integration of the impulse response yields the product of the area function and the scattering constant. This product is also known as the ramp function response or the ramp response. Dividing the ramp response by its integral results the area function per volume of the target (normalized area function)  thus eliminating the unknown scattering constant. Since the area function (or its normalized form) contains the geometric information about the target, it has been employed in studies of both radar [3–5] and ultrasonic signal imaging . In this paper, an ultrasonic CT algorithm is develped, using the area function from the Born approximation previously suggested by Tam . A similar imaging technique for radar signals can be found in an earlier work done by Das and Boerner .
KeywordsImpulse Response Area Function Born Approximation Oblate Spheroid Backprojection Algorithm
Unable to display preview. Download preview PDF.
- 1.J. H. Rose and J. M. Richardson, J. Nondestruc. Eval. a, 45 (1982).Google Scholar
- 2.L. S. Koo, H. R. Shafiee, D. K. Hsu, S. J. Wonnley, and D. O. Thompson, submitted for publication.Google Scholar
- 3.D. L. Moffatt and E. M. Kennaugh, IEEE Trans. on Anten. and Prop. AP-13, 401 (1965).Google Scholar
- 4.J. D. Young, IEEE Trans. on Anten. and Prop. AP-24, 276 (1976).Google Scholar
- 5.Y. Das and W. M. Boerner, IEEE Trans. on Anten. and Prop. AP-26, 274 (1978).Google Scholar
- 6.S. J. Tsao, V. V. Varadan, V. K. Varadan, F. Cohen-Tenoudji, and B. R. Tittmann, IEEE Ultrasonics Sym. Proc. 2, 975 (1984).Google Scholar
- 7.K. C. Tam, J. Nondestruc. Eval. L, 95 (1985).Google Scholar
- 8.G. T. Herman, Image Reconstruction From Prrojections -Fn udamentals of Computerized Tomography ( Academic Press, New York, 1980 ).Google Scholar
- 10.R. H. Huesman, G. T. Gullberg, W. L. Greenberg and T. F. Budinger, Donner Algorithms For Reconstruction Tomography, Lawrence Berkeley Lab., Univ. of Calif., Oct. 1977.Google Scholar
- 12.L. W. Schmerr, C. P. Chiou, and S. M. Nugen, in these proceedings.Google Scholar