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19 March 2014 A spectral CT technique using balanced K-edge filter set
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In this work, we propose a novel spectral computed tomography (CT) approach that combines a conventional CT scanner with a Ross spectrometer to obtain quasi-monoenergetic measurements. The Ross spectrometer, which is a generalization of a Ross filter pair, is a set of balanced K-edge filters whose thicknesses are such that the transmitted spectra through any two filters are nearly identical except in the energy band between their respective K-edges. The proposed approach is based on these specially designed filters, which are used to synthesize a set of quasi-monoenergetic sinograms whose reconstruction yields energy-dependent attenuation coefficient (μE) images. In this way, we are able to collect data using conventional CT data acquisition electronics, then to synthesize spectral CT datasets with highly stable, rate-independent energy bin boundaries. This approach avoids the chromatic distortion due to event pile-up which can cause difficulties with single photon spectrometry-based methods. To validate our Ross Spectrometer CT concept, we performed phantom studies and acquired data with a balanced filter set consisting of thin foils of silver, tin, cerium, dysprosium and tungsten. For each energy bin, a synthesized quasi-monoenergetic CT image was reconstructed using the filtered back projection (FBP) algorithm operating on the logarithmic ratio of corresponding energy-resolved intensity and blank sinogram pairs. The reconstructed attenuation coefficients showed satisfactorily good agreement with NIST reference values of μE for water. The proposed spectral CT technique is potentially feasible and holds promise to provide a more accurate and cost-effective alternative to single-photon counting spectral CT techniques.
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Yothin Rakvongthai, William Worstell, Georges El Fakhri, and Jinsong Ouyang "A spectral CT technique using balanced K-edge filter set", Proc. SPIE 9033, Medical Imaging 2014: Physics of Medical Imaging, 90335M (19 March 2014);

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