Peiffer, Carlo;
(2025)
Strain imaging using multimodal X-ray imaging.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
X-ray strain imaging uses X-ray tomography to visualise internal deformations in loaded samples, with strain measured via digital volume correlation. While effective for highly absorbing materials, strain measurements of low-absorbing materials like soft tissues and polymers become ineffective due to reduced contrast-to-noise ratio, limiting precision and resolution. Phase contrast tomography, using synchrotrons or micro-focus X-ray systems, shows promise but is often inaccessible or limited by a small field of view. In this thesis X-ray strain imaging with two phase contrast methods—edge illumination and two-dimensional beam tracking—compatible with compact X-ray sources up to 100 μm focal spot size is investigated. For edge illumination a molybdenum source is operated at 17.5 keV mean energy, while for two-dimensional beam tracking a tungsten source is operated at 15 keV mean energy. These techniques provide absorption, refraction, and scattering contrast, enhancing resolution without increasing geometric magnification, preserving a larger field of view. The strain retrieval precision is analysed using digital volume correlation across contrast types, sampling conditions, and scanning methods. For edge illumination at 0.5 mm strain spatial resolution, absorption contrast achieves a strain precision of 0.5 × 10−3 for a polymer foam and 1.3 × 10−3 for ethanol-fixed tissue, while phase contrast is less precise (12 × 10−3 for foam, 55 × 10−3 for tissue). For two-dimensional beam tracking at 0.45 mm strain spatial resolution, absorption achieves 0.6 × 10−3 (foam) and 1.7 × 10−3 (tissue), while phase contrast reaches 1.2 × 10−3 (foam) and 6.1 × 10−3 (tissue). In this thesis, two applications are examined: a biomedical study on tumour margin detection using a mechanically realistic phantom with a 3.2 kPa matrix and a 13.9 kPa stiff inclusion, and an industrial study characterising the mechanical deformation of polymer bead foam. The inclusion is identified through the strain field and validated with finite element analysis. Additionally, the potential for inherent strain imaging by using the scattering signal is explored.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Strain imaging using multimodal X-ray imaging |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| Keywords: | X-ray imaging, strain imaging, X-ray phase contrast, computed tomography, Edge illumination, beam tracking, digital volume correlation |
| UCL classification: | UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng UCL |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10206163 |
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