Numeric Evaluation of Backward Wave Propagation Image Reconstruction
The Backward Wave Propagation (BWP) algorithm provides a means for reconstructing an image from spatial wave samples measured across an aperture at discrete transducer locations. The technique performs a spatial wave number decomposition on the aperture samples. This decomposition can be phase adjusted and retransformed back into the space domain taking into account the constraints of the wave equation. In this manner the image “scanned” by the aperture can be reconstructed using primarily Fast Fourier Transform (FFT) techniques. Use of parallel processing incorporating AMD 29500 series VLSI integrated circuits has been described previously to achieve image reconstruction at video rates with each frame derived from a single illuminating pulse. This paper explores the accuracy of the BWP image reconstruction by comparison with known interference patterns. The effects of finite word length arithmetic and noise corruption are examined. The conclusion suggests that the use of the new AMD 29325 series 32 bit floating point circuits will lead to a more robust image reconstruction. The previously reported system has been redesigned to incorporate these new circuits. These new building blocks illustrate once again the dramatic effect VLSI can have on the design of ultrasonic imaging systems.
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