Evaluation of a pulse coding technique for speckle reduction and structure characterization

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Title: Evaluation of a pulse coding technique for speckle reduction and structure characterization
Author: Rao, Navalgund; Abury, M.
Abstract: Pulse coding techniques have been used in the past primarily to improve signal to (electronic) noise ratio. However, the flexibility inherent in pulse coding can be exploited to solve several problems in medical imaging and nondestructive testing. We have experimentally examined its potential for two such problems: (i) speckle reduction with multispectral imaging and data averaging; (ii) structural characterization of scattering medium on a scale below the resolution of the imaging system. The ability to change the point spread function and the spectral content with frequency modulated pulse coding has been utilized. Water filled sponge with pore size much smaller than the resolution cell volume was used as a speckle generating medium. A non-focused transducer was driven with FM coded pulses. The pulse compression processing was carried out digitally on a computer. FM pulses with 143 different combinations of center frequency f0 and 6 dB bandwidth Δf were used. Normalized decorrelation factors were calculated to evaluate effectiveness for speckle averaging. Significant decorrelation was observed specially at lower Δf, indicating a potential for frequency diversity processing for speckle reduction. Point signal to noise ratio (SNRA) was also calculated on the envelope detected signal for structural characterization. SNRA showed significant increase from its high density limit value of 1.91 (fully developed speckle) at certain specific frequencies. Both simulation and theoretical considerations are used to show that this resonance effect is a signature of the underlying semiperiodic scattering structure of the medium (Refer to PDF file for exact formulas).
Description: "Evaluation of a pulse coding technique for speckle reduction and structure characterization," Proceedings of the 1993 Ultrasonics Symposium. Institute of Electrical and Electronics Engineers. Held in Baltimore, Maryland: 31 October - 3 November 1993. ©1993 Institute of Electrical and Electronics Engineers (IEEE). Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.
Record URI: http://hdl.handle.net/1850/3215
Date: 1993-10-31

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