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Modelling the penumbra in computed tomography

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Kueh, Audrey, Warnett, Jason M., Gibbons, Gregory John, Brettschneider, Julia, Nichols, Thomas E., Williams, M. A. and Kendall, W. S. (2016) Modelling the penumbra in computed tomography. Journal of X-Ray Science and Technology, 24 (4). pp. 583-597. doi:10.3233/XST-160576

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Official URL: http://dx.doi.org/10.3233/XST-160576

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Abstract

Background:

In computed tomography (CT), the spot geometry is one of the main sources of error in CT images. Since X-rays do not arise from a point source, artefacts are produced. In particular there is a penumbra effect, leading to poorly defined edges within a reconstructed volume. Penumbra models can be simulated given a fixed spot geometry and the known experimental setup.

Objective:

This paper proposes to use a penumbra model, derived from Beer’s law, both to confirm spot geometry from penumbra data, and to quantify blurring in the image. Methods: Two models for the spot geometry are considered; one consists of a single Gaussian spot, the other is a mixture model consisting of a Gaussian spot together with a larger uniform spot. Results: The model consisting of a single Gaussian spot has a poor fit at the boundary. The mixture model (which adds a larger uniform spot) exhibits a much improved fit. The parameters corresponding to the uniform spot are similar across all powers, and further experiments suggest that the uniform spot produces only soft X-rays of relatively low-energy.

Conclusions:

Thus, the precision of radiographs can be estimated from the penumbra effect in the image. The use of a thin copper filter reduces the size of the effective penumbra.

Item Type: Journal Article
Subjects: R Medicine > R Medicine (General)
Divisions: Faculty of Science > Statistics
Faculty of Science > WMG (Formerly the Warwick Manufacturing Group)
Library of Congress Subject Headings (LCSH): Tomography -- Data processing
Journal or Publication Title: Journal of X-Ray Science and Technology
Publisher: I O S Press
Official Date: 20 July 2016
Dates:
DateEvent
10 April 2016Accepted
20 July 2016Published
Volume: 24
Number: 4
Page Range: pp. 583-597
DOI: 10.3233/XST-160576
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Open Access
RIOXX Funder/Project Grant:
Project/Grant IDRIOXX Funder NameFunder ID
EP/K031066/1[EPSRC] Engineering and Physical Sciences Research Councilhttp://dx.doi.org/10.13039/501100000266
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