| 1. |
- Hertz, Hans M., et al.
(author)
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Propagation-based phase-contrast imaging with laboratory sources
- 2016
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In: Optics InfoBase Conference Papers. - Washington, D.C. : OSA - The Optical Society. - 9781943580095
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Conference paper (peer-reviewed)abstract
- We demonstrate that propagation-based phase-contrast x-ray imaging with state-of-the art laboratory microfocus sources allows imaging of thick biomedical objects with very high spatial resolution.
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| 2. |
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| 3. |
- Häggmark, Ilian, et al.
(author)
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Comparison of quantitative multi-material phase-retrieval algorithms in propagation-based phase-contrast X-ray tomography
- 2017
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In: Optics Express. - : The Optical Society. - 1094-4087. ; 25:26, s. 33543-33558
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Journal article (peer-reviewed)abstract
- Propagation-based phase-contrast X-ray imaging provides high-resolution, dose-efficient images of biological materials. A crucial challenge is quantitative reconstruction, referred to as phase retrieval, of multi-material samples from single-distance, and hence incomplete, data. In this work, the two most promising methods for multi-material samples, the parallel method, and the linear method, are analytically, numerically, and experimentally compared. Both methods are designed for computed tomography, as they rely on segmentation in the tomographic reconstruction. The methods are found to result in comparable image quality, but the linear method provides faster reconstruction. In addition, as already done for the parallel method, we show that the linear method provides quantitative reconstruction for monochromatic radiation.
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| 4. |
- Larsson, Daniel, 1985-
(author)
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Small-Animal Imaging with Liquid-Metal-Jet X-Ray Sources
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Small-animal x-ray imaging is an important tool for medical research. The penetration power of x-rays makes it possible to investigate the 3D structure of small animals and other thick biological samples by computed tomography (CT). However, small-animal x-ray imaging often requires high resolution due to the small structures involved, and short exposure times due to sample movement. This constitutes a challenge, since these two properties require compact x-ray sources with parameters that are not widely available.In this Thesis we present the first application of liquid-metal-jet sources for small-animal imaging. This source concept was invented at KTH just over ten years ago. The use of a high-speed metal jet as electron-beam target, instead of a solid anode, enables higher x-ray flux while maintaining a small x-ray spot for high-resolution imaging. In the present work, a liquid-metal jet source with a higher-energy spectrum has been developed. It has stronger 24 keV radiation compared to previous sources, which makes it more suitable for imaging of small animals and other few-cm-thick objects, which require the higher penetration of 20-35 keV x-rays.We have applied the liquid-metal-jet x-ray sources for whole-body imaging of sacrificed mice and zebrafish. With high-resolution absorption-contrast CT we have visualized fine bone details of mice. We have also used phase contrast, a new method that can considerably improve imaging of, e.g., soft tissue, for demarcation of mm-sized tumors inside a full mouse and for mouse cartilage imaging. In zebrafish imaging, we have exploited the greatly enhanced contrast of phase-imaging to resolve single muscle fibers (and possibly even myofibrils) in whole zebrafish in a laboratory setting for the first time. The muscle structures have diameters in the 5-7 μm range and extremely low contrast, which makes them difficult to observe.With phase contrast, we have demonstrated low-dose and high-resolution angiography of mouse and rat organs and tissues ex vivo. We show detection of blood vessels with diameters below 10 μm with radiation doses compatible with living small animals, which is not possible with absorption contrast and iodinated contrast agents. In addition, we have investigated the vascular network of tumors in mouse ears and visualized the chaotic arrangement of newly-formed blood vessels.Finally, we present the first results from a new high-power liquid-metal-jet x-ray source prototype, operating at 10× the power of our previous sources, with the same x-ray spot size. This source constitutes an important step towards future in-vivo small-animal laboratory imaging with high resolution.
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| 5. |
- Larsson, Jakob C.
(author)
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Laboratory x-ray fluorescence tomography
- 2018
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Doctoral thesis (other academic/artistic)abstract
- X-ray fluorescence (XRF) tomography is an emerging bio-imaging modality with potential for high-resolution molecular imaging in 3D. In this technique the fluorescence signal from targeted nanoparticles (NPs) is measured, providing information about the spatial distribution and concentration of the NPs inside the object. However, present laboratory XRF tomographysystems typically have limited spatial resolution (>1 mm) and suffer from long scan times and high radiation dose even at high NP concentrations, mainly due to low efficiency and poor signal-to-noise ratio (SNR). Other macroscopic biomedical imaging methods provide either structural information with high spatial resolution (e.g., CT) or functional/molecularinformation with lower resolution (e.g., PET).In this Thesis we present a laboratory XRF tomography system with high spatial resolution (sub-200 μm), low NP concentration and vastly reduced scan times and dose, opening up the possibilities for in vivo small-animal imaging research. The system consists of a high-brightness liquid-metal-jet microfocus x-ray source, x-ray focusing optics and two photon counting detectors. By using the source’s characteristic 24 keV line emission together with spectrally matched molybdenum NPs the Compton background is greatly reduced, increasing the SNR. Each measurement provides information about the spatial distribution and concentration of the NPs, as well as the absorption of the object. An iterative method is used to get aquantitative reconstruction of the XRF image. The reconstructed absorption and XRF images are finally combined into a single 3D overlay image.Using this system we have demonstrated high-resolution dual CT and XRF imaging of both phantoms and mice at radiation doses compatible with in vivo small-animal imaging.
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| 6. |
- Romell, Jenny, et al.
(author)
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Comparison of laboratory grating-based and speckle-tracking x-ray phase-contrast imaging
- 2017
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In: X-Ray Microscopy Conference 2016 (XRM 2016)15–19 August 2016, Oxford University, United Kingdom. - : Institute of Physics Publishing (IOPP).
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Conference paper (peer-reviewed)abstract
- Phase-contrast imaging with x-rays is a developing field for imaging weakly absorbing materials. In this work, two phase-contrast imaging methods, grating- and speckle-based imaging, that measure the derivative of the phase shift, have been implemented with a laboratory source and compared experimentally. It was found that for the same dose conditions, the speckle-tracking differential phase-contrast images have considerably higher contrast-to-noise ratio than the grating-based images, but at the cost of lower resolution. Grating-based imaging performs better in terms of resolution, but would require longer exposure times, mainly due to absorption in the grating interferometer.
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| 7. |
- Twengström, William
(author)
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High-resolution biomedical phase-contrast tomography
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Improved three-dimensional biomedical imaging can give a better understanding of tissue structure, growth and diseases. Most present imaging techniques that provide cellular spatial resolution are based on visible or infrared light. These methods cannot image deeper than a millimeter into tissue. Consequently, larger samples cannot be completely imaged without sectioning. Techniques that are typically used to image larger samples don't provide sufficient contrast and resolution to image cellular-sized features in soft tissues. There is a need for new imaging methods that can fill the gap between present methods. For practical reasons, compact equipment is preferred, to enable close connection to other research and applications. Furthermore, minimized sample preparation both reduces the work needed and the time until results are ready.In this Thesis, propagation-based phase-contrast tomography with liquid-metal-jet x-ray sources has been investigated for high-resolution three-dimensional biomedical imaging. By using phase contrast, the contrast for cellular-sized features in soft tissue is vastly increased compared to absorption, also in larger samples. The high resolution relies on using an x-ray source with small emission spot, but also with high power to keep exposure times reasonable.This Thesis is about developing and optimizing experimental methods and image reconstruction algorithms. A new method to remove ring artifacts was developed and tested, and a comparison of multi-material phase-retrieval algorithms was made. The improvements provide better contrast and resolution, as well as reduce noise and artifacts. The improved image quality is demonstrated in a few biomedical applications. It is shown that the method can image 5 µm large myofibrils in whole-body zebrafish, despite the small size and low contrast of myofibrils. A high-resolution tomography of a mouse can be done fast by using a specialized high-power source. The image quality in tomographies of both human coronary arteries and a mummified human hand is sufficient to analyze the tissues and cellular-sized features, which is something that could be called virtual histology.
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| 8. |
- Zanette, I., et al.
(author)
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X-ray microtomography using correlation of near-field speckles for material characterization
- 2015
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In: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 112:41, s. 12569-12573
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Journal article (peer-reviewed)abstract
- Nondestructive microscale investigation of objects is an invaluable tool in life and materials sciences. Currently, such investigation is mainly performed with X-ray laboratory systems, which are based on absorption-contrast imaging and cannot access the information carried by the phase of the X-ray waves. The phase signal is, nevertheless, of great value in X-ray imaging as it is complementary to the absorption information and in general more sensitive to visualize features with small density differences. Synchrotron facilities, which deliver a beam of high brilliance and high coherence, provide the ideal condition to develop such advanced phase-sensitive methods, but their access is limited. Here we show how a small modification of a laboratory setup yields simultaneously quantitative and 3D absorption and phase images of the object. This single-shot method is based on correlation of X-ray near-field speckles and represents a significant broadening of the capabilities of laboratory- based X-ray tomography.
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| 9. |
- Zhou, Tunhe
(author)
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Laboratory X-Ray Phase-Contrast Imaging : Methods and Comparisons
- 2016
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Doctoral thesis (other academic/artistic)abstract
- X-ray phase-contrast imaging has seen rapid development in recent decades due to its superior performance in imaging low-absorption objects, compared to traditional attenuation x-ray imaging. Having higher demand on coherence, x-ray phase-contrast imaging is performed mostly at synchrotrons. With the development of different imaging techniques, and the development of laboratory sources and x-ray optics, x-ray phase-contrast imaging can now be implemented on laboratory systems, which is promising and practical for broader range of applications.The subject of this thesis is the implementation, development and comparison of different laboratory phase-contrast methods using a liquid-metal-jet source. The three x-ray phase-contrast imaging methods included in this thesis are the propagation-, grating-, and speckle-based techniques. The grating-based method has been implemented on a laboratory system with a liquid-metal-jet source, which yields several times higher brightness than a standard solid-anode microfocus source. This allows shorter exposure time or a higher signal-to-noise ratio. The performance of the grating-based method has been experimentally and numerically compared with the propagation-based method, and the dose required to observe an object as a function of the object’s diameter has been investigated with simulations. The result indicates a lower dose requirement for the propagation-based method in this system but a potential advantage for the grating-based method to detect relatively large samples using a monochromatic beam.The speckle-based method, both the speckle-tracking and speckle-scanning techniques, has been implemented on a laboratory system for the first time, showing its adaptability to radiation of low temporal coherence. Tomography has been performed and shows the potential applications of this method on quantitative analysis on both absorption and phase information of materials. As a basis for further optimization and comparisons to other methods, the noise properties of the differential phase contrast of the speckle-based method have been studied and an analytical expression for the noise variance introduced, showing a similarity to the grating-based method.
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| 10. |
- Zhou, Tunhe, et al.
(author)
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Noise analysis of speckle-based x-ray phase-contrast imaging
- 2016
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In: Optics Letters. - : The Optical Society. - 0146-9592 .- 1539-4794. ; 41:23, s. 5490-5493
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Journal article (peer-reviewed)abstract
- Speckle-based x-ray phase-contrast imaging has drawn increasing interest in recent years as a simple, multimodal, cost-efficient, and laboratory-source adaptable method. We investigate its noise properties to help further optimization on the method and further comparison with other phase-contrast methods. An analytical model for assessing noise in a differential phase signal is adapted from studies on the digital image correlation technique in experimental mechanics and is supported by simulations and experiments. The model indicates that the noise of the differential phase signal from speckle-based imaging has a behavior similar to that of the grating-based method.
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