| 1. |
- Häggmark, Ilian
(author)
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Phase-Contrast X-Ray Imaging of Complex Objects
- 2021
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Doctoral thesis (other academic/artistic)abstract
- X-ray imaging is a group of techniques using electromagnetic radiation of high energy. The ability to quickly visualize internal structures in thick opaque objects has made it an indispensable tool in research, medicine, and industry. Contrast is generally achieved by differential absorption, however, this mechanism has a strong dependence on atomic number. This results in low contrast within materials consisting of mainly elements of low atomic number, such as hydrogen, carbon and oxygen, e.g., soft organic matter. The problem with low contrast is further complicated by limitations in radiation dose. To improve contrast the phase shift of the X-rays can be measured without increasing the dose.This Thesis concerns one method to harness this phase signal – propagation-based phase-contrast X-ray imaging (PBI). Three aspects on how to image complex objects are addressed: multi-material phase retrieval, simulations of clinical imaging, and small-animal imaging on compact systems. First, the derivation of a previously published method for multi-material phase retrieval is shown. A comparison between this method and another further reveals important differences. Secondly, a strategy to use large digital voxel-based phantoms for clinical imaging is developed. The method is demonstrated on a mammography phantom and in a reader study on clinical lung imaging. Finally, a compact X-ray system is used to demonstrate imaging of vascular canals in rat bone and high-resolution lung imaging on free-breathing mice, i.e., without mechanical ventilation.
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| 2. |
- Rezasson, Reza, 1985-, et al.
(author)
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A fast and non-destructive alternative to the burnout method for paperboard quality inspections using phase-contrast X-ray imaging
- 2023
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In: TAPPI Journal. - : TAPPI. - 0734-1415. ; 22:2, s. 99-106
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Journal article (peer-reviewed)abstract
- An X-ray based quality inspection method for paperboard was implemented and tested as a fastand non-destructive alternative to the burnout method. An argument against X-ray imaging for inspection of paperand paperboard has been that X-ray absorption is low in paper. To overcome this limitation, we used phase-contrastX-ray imaging (PCXI), which gives higher contrast than conventional attenuation-based imaging for low-absorbingmaterials such as paper. The suggested PCXI method was applied to previously prepared and quality rated samplesusing the burnout method.A strong similarity between the burnout images and the PCXI images was observed. In conclusion, further devel-opment of the phase-contrast X-ray method would provide an interesting option for replacing or complementing thestandard burnout method.
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| 3. |
- Romell, Jenny
(author)
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Virtual histology by laboratory x-ray phase-contrast tomography
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Detailed imaging of biological samples is central to different fields of research, as well as for clinical pathology. Classical histology, using light- orelectron microscopy, can generate high-resolution images but is destructive and only gives two-dimensional information. With virtual histology, athree-dimensional reconstruction of the sample is instead generated, whichcan be virtually sectioned in arbitrary directions. This Thesis presents developments of x-ray phase-contrast computed tomography (CT) as a tool forvirtual histological analysis. In particular, the focus is imaging with laboratory systems as opposed to at large-scale synchrotron facilities, and usingphase-contrast imaging as an alternative to chemical contrast agents.A broad range of imaging applications are demonstrated, from archaeology to clinical pathology, where acquisition and data processing have beenoptimised for each sample. A micro-CT system based on a liquid-metaljet x-ray source was used for imaging centimetre-sized samples. Threedimensional imaging of mummified remains was demonstrated, with sufficient contrast and resolution within the soft tissue to capture microanatomical details; blood vessels, skin layers, fingerprints and remains of adiposecells were visualised in the hand of an ancient Egyptian mummy. Virtualhistology was also performed on paraffin-embedded excised tumours foranalysis of the resection margin, and on rat bones for mapping the vascularcanals.For imaging with micrometre resolution, a nano-CT system was builtand characterised. Photoreceptor imaging in unstained compound eyes ofbumblebees was demonstrated, and light- and electron microscopy wereused to verify the results. Comparisons with conventional attenuationmicro-CT and synchrotron radiation tomography, with both unstained andstained samples, showed the advantage of using phase contrast instead ofstaining the samples
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| 4. |
- Shaker, Kian
(author)
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Preclinical X-ray imaging beyond attenuation contrast
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Medical imaging is a cornerstone of modern clinical practice. Here, X-ray imaging is the given choice for rapid morphological imaging with excellent spatial resolution, albeit with sensitivity often insufficient for resolving subtle pathological changes to soft tissues. Fundamentally, the sensitivity issue is due to the image contrast traditionally being based on differential X-ray attenuation (i.e., absorption and scattering) where attenuation properties of soft tissues are often very similar. Improving the sensitivity of clinical X-ray imaging therefore requires moving beyond conventional attenuation contrast.Motivated by the above, this Thesis explores two alternative contrast mechanisms in the preclinical domain, yet with a clinical outlook: X-ray fluorescence and X-ray phase contrast. These mechanisms are demonstrated both experimentally on animal models (in vivo) and computationally on virtual anatomical phantoms (in silico). Specifically, we developed instrumentation for in vivo X-ray fluorescence imaging of mice injected with nanoparticle contrast agents, demonstrating a path towards molecular X-ray imaging with higher spatial resolution (< 0.5 mm) than established molecular modalities (e.g., PET & SPECT) and roughly 10× higher sensitivity (~ 0.1 mM) compared to conventional attenuation contrast. Furthermore, we showed that the terminal bronchioles (diameters down to ~ 60 μm) could be resolved in free-breathing mice under anesthesia using X-ray imaging boosted by phase contrast. Lastly, we showed through in silico modeling that the extension of X-ray phase contrast to human lungs could potentially enable visualization of small airways (diameters below 2 mm) which are invisible to attenuation contrast alone. In summary, this Thesis provides experimental and computational demonstrations indicating that both X-ray fluorescence and X-ray phase contrast could provide a path towards clinical X-ray imaging with improved sensitivity.
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