Virtual Reduction of Focal Spot Size in Computed Tomography using Collimation

Master thesis (2023)

Authors

D. Boeke Mechanical Engineering

Contributors

M.C. Goorden RST/Biomedical Imaging - AS (mentor)
F.J. Beekman RST/Biomedical Imaging - AS (graduation committee member)
D. Lathouwers RST/Reactor Physics and Nuclear Materials - AS (graduation committee member)
Faculty
Mechanical Engineering, Mechanical Engineering
Copyright: © 2023 Daan Boeke
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Published Date

31-01-2023

Language

English

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Faculty

Mechanical Engineering

Abstract

This thesis aimed to validate Beekman's patent on how collimation could virtually reduce the focal spot size of an existing small-animal cone beam Computed Tomography (CT) system to diminish the penumbra effect. The ever-remaining drive to improve the spatial resolution in CT for enhanced image quality introduces the need for small focal spot sizes, as the focal spot size is directly related to the geometric unsharpness in the image. Therefore, a collimation method was proposed to virtually reduce the focal spot of existing systems as an alternative to fully replace the current X-ray tube.

A collimator was designed, consisting of numerous tiny hexagonal-shaped holes focused at the center of the focal spot. Theoretical derivations were formulated for its dimensions, and the collimator's efficacy was validated using Monte Carlo simulations. It was concluded that it is theoretically achievable to use collimation to virtually reduce the focal spot size to an arbitrarily chosen smaller virtual focal spot for existing CT systems, significantly reducing the penumbra effect, without requiring any integral changes to the X-ray tube. However, the collimator's practical suitability and manufacturing feasibility were problematic due to its significantly low collimator sensitivity and exceptionally tiny dimensions.

Future work could build on this thesis by obtaining reconstructions from multiple projections of the virtual focal spot to quantitatively assess their theoretically improved spatial resolution. The quantitative confirmation could further establish the theoretical effectiveness of focal spot collimation for future work to enhance reconstructions to uncover valuable information previously hidden.