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Proceedings Paper

Investigation of coherent-scatter computed tomography
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Paper Abstract

Conventional computed tomography (CT) images are `maps' of the x ray linear attenuation coefficient within a slice through an object. A novel approach to CT is being developed which instead produces tomographic images based on an object's low-angle (0 - 10 degree(s)) x-ray diffraction properties. The coherent-scatter cross sections of many materials vary greatly, and this coherent-scatter CT (CSCT) system gives material-specific information on this basis. The goal of this research is to produce tomographic maps of bone-mineral content (BMC), first in laboratory specimens, and potentially in patients. The concept of reconstructing tomographic images using coherently scattered x rays was first demonstrated by Harding et al. The approach described here is a modification of their method. First generation CT geometry is used in which a diffraction pattern is acquired for each pencil-beam using a CsI image intensifier coupled to a CCD. Each pattern is sectioned into concentric annular rings so that the integrated signal in each ring gives the scatter intensity at a particular scatter angle, integrated along the path through the object. An image is reconstructed for each ring, resulting in a series of tomographic images corresponding to the scatter intensity at a series of scatter angles. A test phantom was imaged (70 kVp, 50 mAs per exposure, 100 mSv average dose) to demonstrate CSCT. The phantom consists of a water-filled Lucite cylinder containing rods of polyethylene, Lucite, polycarbonate, and nylon. The resulting series of images was used to extract the angular-dependent scatter cross section for every pixel. Using pure material cross sections as basis functions, the cross section from each pixel was fitted using non-negative least squares. The results were used to create material-specific images. These results show that CSCT is feasible with this approach and that if the materials in an object have distinguishable scatter cross sections, the method has the ability to identify the materials. It may be possible to image the BMC distribution as trabecular bone mineral is replaced by lipids.

Paper Details

Date Published: 8 May 1995
PDF: 9 pages
Proc. SPIE 2432, Medical Imaging 1995: Physics of Medical Imaging, (8 May 1995); doi: 10.1117/12.208349
Show Author Affiliations
Michael S. Westmore, John P. Robarts Research Institute and Univ. of Western Ontario (Canada)
Aaron Fenster, John P. Robarts Research Institute and Univ. of Western Ontario (Canada)
Ian A. Cunningham, John P. Robarts Research Institute, Univ. of Western Ontario, and Victoria Hospital (Canada)

Published in SPIE Proceedings Vol. 2432:
Medical Imaging 1995: Physics of Medical Imaging
Richard L. Van Metter; Jacob Beutel, Editor(s)

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