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Proceedings Paper

Time-lapse x-ray microtomography for detecting small changes in local mineral concentration
Author(s): Graham Davis
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Paper Abstract

When using X-ray microtomography (XMT) to look for small mineral changes between successive scans in, for example, extracted human teeth, it is necessary to use a carefully designed protocol to ensure maximum accuracy. Our protocol is divided into four main elements: Mounting: The sample, in this case a tooth, must be mounted in such a way that it can be precisely relocated in the same place in the scanner (height and tilt must be precise; rotation can be changed post-scanning). Calibration: Over time (possibly weeks or months), the X-ray spectrum may change (with anode potential and current constant). This is due primarily to gradual anode pitting, which causes varying amounts of self-absorption. A calibration carousel is used to characterize the X-ray spectrum after every scan. Alignment: To ensure that the same regions are measured for every scan, it is necessary that all reconstructed images are perfectly aligned. We use a 7 degree-of-freedom alignment algorithm for this. To avoid loss of resolution when realigning data sets, second and subsequent scans are reconstructed with a 2× scale factor and “shrunk” during the realignment. Equalization: In spite of best efforts for calibration, repeatability for linear attenuation coefficient (LAC) measurement is of the order of 1%. To improve on this, regions are defined in which no change in mineral concentration should occur. In every scan, the mean LAC for these regions is measured and an appropriate LAC scaling factor is applied to the reconstructed volumes for the second and subsequent scans.

Paper Details

Date Published: 10 September 2019
PDF: 6 pages
Proc. SPIE 11113, Developments in X-Ray Tomography XII, 1111315 (10 September 2019); doi: 10.1117/12.2529334
Show Author Affiliations
Graham Davis, Queen Mary Univ. of London (United Kingdom)

Published in SPIE Proceedings Vol. 11113:
Developments in X-Ray Tomography XII
Bert Müller; Ge Wang, Editor(s)

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