Digital medical images used in radiology are quite different to everyday continuous tone images. Radiology images require that all detailed diagnostic information can be extracted, which traditionally constrains digital medical images to be of large size and stored without loss of information. In order to transmit diagnostic images over a narrowband wireless communication link for remote diagnosis, lossy compression schemes must be used. This involves discarding detailed information and compressing the data, making it more susceptible to error. The loss of image detail and incidental degradation occurring during transmission have potential legal accountability issues, especially in the case of the null diagnosis of a tumor. The work proposed here investigates techniques for verifying the voracity of medical images -in particular, detailing the use of embedded watermarking as an objective means to ensure that important parts of the medical image can be verified. We propose a result to show how embedded watermarking can be used to differentiate contextual from detailed information. The type of images that will be used include spiral hairline fractures and small tumors, which contain the essential diagnostic high spatial frequency information.
The implementation of wavelets in differing areas of signal processing has been a popular research area over the last decade. However, utilising this technology in compressing two dimensional signals, such as digital images is relatively new. Wavelet compression has many distinct advantages over earlier compression methods, the most important of which is suitability to error protection as well as the ability to precisely truncate the compressed bitstream to achieve a desired bit rate for transmission. In this paper some of the recently emerging technologies pertaining to wavelet coding of images will be reviewed, particularly with the use of wireless channels. These developments include techniques to filter images that have been degraded through the addition of noise as well as reconstructing parts of images that have been lost as a result of the fading that characterises wireless mobile environments.
The synthesis of kinetically-stabilized, i.e., metastable, dielectric semiconductors, represents a major frontier within key technologically-important fields as compared to thermodynamically-stable solids that have received considerably more attention. Of longstanding theoretical interest are Sn(II) perovskites (e.g., Sn(Zr1/2Ti1/2)O3, SZT), which are Pb-free analogues of (Pb(Zr1/2Ti1/2)O3, PZT), a commercial piezoelectric composition that is dominant in the electronics industry. Herein, we describe the synthesis of this metastable SZT dielectric through a low-temperature flux reaction technique. The SZT has been found, for the first time, to grow and to be stabilized as a nanoshell at the surfaces of Ba(Zr1/2Ti1/2)O3 (BZT) particles, i.e., forming as BZT-SZT core-shell particles, as a result of Sn(II) cation exchange. In situ powder X-ray diffraction (XRD) and transmission electron microscopy data show that the SZT nanoshells result from the controlled cation diffusion of Sn(II) cations into the BZT particles, with tunable thicknesses of ~25 nm to 100 nm. The SZT nanoshell is calculated to possess a metastability of ~ 0.5 eV atom–1 with respect to decomposition to SnO, ZrO2, and TiO2, and thus cannot currently be prepared as stand-alone particles. Rietveld refinements of the XRD data are consistent with a two-phase BZT-SZT model, with each phase possessing a generally cubic perovskite-type structure and nearly identical lattice parameters. Mössbauer spectroscopic data (119Sn) are consistent with Sn(II) cations within the SZT nanoshells and an outer ~5 to 10 nm surface region comprised of oxidized Sn(IV) cations from exposure to air and water. The optical band gap of the SZT shell was found to be ~2.2 eV, which is redshifted by ~1.2 eV as compared to BZT. This closing of the band gap was probed by X-ray photoelectron spectroscopy and found to stem from a shift of the valence band edge to higher energies (~1.07 eV) as a result of the addition of the Sn 5s2 orbitals forming a new higher-energy valence band. In summary, a novel synthetic tactic is demonstrated to be effective in preparing highly metastable SZT and representing a generally useful strategy for the kinetic stabilization of other predicted, metastable dielectrics.
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