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Proceedings Paper

Multi-species beam hardening calibration device for x-ray microtomography
Author(s): Anthony N. Z. Evershed; David Mills; Graham Davis
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Paper Abstract

Impact-source X-ray microtomography (XMT) is a widely-used benchtop alternative to synchrotron radiation microtomography. Since X-rays from a tube are polychromatic, however, greyscale ‘beam hardening' artefacts are produced by the preferential absorption of low-energy photons in the beam path.

A multi-material ‘carousel' test piece was developed to offer a wider range of X-ray attenuations from well-characterised filters than single-material step wedges can produce practically, and optimization software was developed to produce a beam hardening correction by use of the Nelder-Mead optimization method, tuned for specimens composed of other materials (such as hydroxyapatite [HA] or barium for dental applications.) The carousel test piece produced calibration polynomials reliably and with a significantly smaller discrepancy between the calculated and measured attenuations than the calibration step wedge previously in use.

An immersion tank was constructed and used to simplify multi-material samples in order to negate the beam hardening effect of low atomic number materials within the specimen when measuring mineral concentration of higher-Z regions. When scanned in water at an acceleration voltage of 90 kV a Scanco AG hydroxyapatite / poly(methyl methacrylate) calibration phantom closely approximates a single-material system, producing accurate hydroxyapatite concentration measurements. This system can then be corrected for beam hardening for the material of interest.

Paper Details

Date Published: 17 October 2012
PDF: 12 pages
Proc. SPIE 8506, Developments in X-Ray Tomography VIII, 85061N (17 October 2012); doi: 10.1117/12.928933
Show Author Affiliations
Anthony N. Z. Evershed, Queen Mary, Univ. of London (United Kingdom)
David Mills, Queen Mary, Univ. of London (United Kingdom)
Graham Davis, Queen Mary, Univ. of London (United Kingdom)

Published in SPIE Proceedings Vol. 8506:
Developments in X-Ray Tomography VIII
Stuart R. Stock, Editor(s)

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