Algebraic Reconstruction Methods for Complex Geometry Components

Industrial CT has seen widespread adoption as an inspection technique due to its ability to resolve small defects and perform high-resolution measurements on complex structures in Non Destructive Testing (NDT). The majority of the commercial cabinet systems are capable of acquisition and reconstruction of Cone Beam CT (CBCT) data utilising reconstruction algorithms such as the FDK, which are mathematically based on traditional FBP. While these algorithms are computationally efficient, limitations in the acquisition make inspection of large complex geometry components challenging. More recently iterative reconstruction algorithms have seen a resurgence of research interest as computing power has increased. Iterative reconstruction algorithms use an alernative reconstruction approach based on linear algebra to calculate the reconstructed image, offering a more precise model for CT reconstruction but at the cost of computational complexity and reconstruction time. This work presents a novel acquisition and reconstruction strategy for arbitrary scanning strategies that extend beyond the circular or helical acquisition for FBP based techniques. The flexibility exposed by arbitrary trajectories allows component specific trajectories to optimise the reconstruction quality through increased accuracy or minimisation of common CT reconstruction artefacts, including mathematically exact reconstruction by satisfying well known CT data-sufficiency conditions. The ability to perform volume reconstruction from arbitrary trajectories is beneficial within NDT for automated robotic inspection. For full 3D reconstruction, voxel weighting schemes currently in use offer only approximations leading to numerical inaccuracies. The AIM for 2D reconstruction is mathematically exact but considers the divergent nature of a fan beam for 2D only. For a full 3D volumetric reconstruction, the x-ray cone beam is divergent in all directions and therefore the AIM technique cannot be applied in its current form. A mathematically exact fractional volume weighting approach, referred to as the VIM, is presented for 3D volumetric image reconstruction with data acquired with a divergent cone beam. While arbitrary scanning trajectories have clear benefits for acquisition with no restriction on access to the component, this is not always feasible for in-situ inspection. This work goes on to further develop the concept of arbitrary scanning by allowing modification of the source to detector distance throughout the scan. This is demonstrated with a minimum bounding ellipsoid trajectory that shows an improvement in the localised image quality for limited angular, non circular trajectories. This approach has potential for targeted in-situ inspection with limited access to the component.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Wales Trinity Saint David

Year dc:date.issued

2024

Author dc:creator

• Hanna, Ross

• Q Gwyddoniaeth (Cyffredinol)

Dc Identifier Grantnumber

UWTSD

OAI identifier oai:identifier

oai:repository.uwtsd.ac.uk:2991