| 1. |
- Burvall, Anna, 1976-
(författare)
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Axicon imaging by scalar diffraction theory
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Axicons are optical elements that produce Bessel beams,i.e., long and narrow focal lines along the optical axis. Thenarrow focus makes them useful ine.g. alignment, harmonicgeneration, and atom trapping, and they are also used toincrease the longitudinal range of applications such astriangulation, light sectioning, and optical coherencetomography. In this thesis, axicons are designed andcharacterized for different kinds of illumination, using thestationary-phase and the communication-modes methods. The inverse problem of axicon design for partially coherentlight is addressed. A design relation, applicable toSchell-model sources, is derived from the Fresnel diffractionintegral, simplified by the method of stationary phase. Thisapproach both clarifies the old design method for coherentlight, which was derived using energy conservation in raybundles, and extends it to the domain of partial coherence. Thedesign rule applies to light from such multimode emitters aslight-emitting diodes, excimer lasers and some laser diodes,which can be represented as Gaussian Schell-model sources. Characterization of axicons in coherent, obliqueillumination is performed using the method of stationary phase.It is shown that in inclined illumination the focal shapechanges from the narrow Bessel distribution to a broadasteroid-shaped focus. It is proven that an axicon ofelliptical shape will compensate for this deformation. Theseresults, which are all confirmed both numerically andexperimentally, open possibilities for using axicons inscanning optical systems to increase resolution and depthrange. Axicons are normally manufactured as refractive cones or ascircular diffractive gratings. They can also be constructedfrom ordinary spherical surfaces, using the sphericalaberration to create the long focal line. In this dissertation,a simple lens axicon consisting of a cemented doublet isdesigned, manufactured, and tested. The advantage of the lensaxicon is that it is easily manufactured. The longitudinal resolution of the axicon varies. The methodof communication modes, earlier used for analysis ofinformation content for e.g. line or square apertures, isapplied to the axicon geometry and yields an expression for thelongitudinal resolution. The method, which is based on abi-orthogonal expansion of the Green function in the Fresneldiffraction integral, also gives the number of degrees offreedom, or the number of information channels available, forthe axicon geometry. Keywords:axicons, diffractive optics, coherence,asymptotic methods, communication modes, information content,inverse problems
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| 2. |
- Burvall, Anna, et al.
(författare)
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Communication modes applied to axicons
- 2004
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Ingår i: Optics Express. - 1094-4087. ; 12:3, s. 377-383
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Tidskriftsartikel (refereegranskat)abstract
- The communication modes, which constitute a convenient method for the propagation and information analysis of optical fields, are formulated in the generalized axicon geometry. The transmitting region is the axicon’s annular aperture, and the observation domain is the optical axis containing the focal line segment. We show that in rotational symmetry one may employ the prolate spheroidal wave functions to represent the communication modes. Further, in usual circumstances the modes can be approximated by quadratic waves in the aperture domain and by sinc functions in the image domain. Both the exact communication modes and the approximate technique are confirmed numerically, with linear axicons as examples.
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| 3. |
- Burvall, Anna, 1976-, et al.
(författare)
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Communication modes for information content analysis
- 2004
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Ingår i: LFNM 2004. - : IEEE conference proceedings. - 0780384296 ; , s. 112-114
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Approximate modes which give physical understanding for the communication modes theory,are discussed. For the geometry consisting of two line or square apertures, perpendicular to the optical axis, this approximation leads to exactly the same modes as Gabor's theory would yield.
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| 4. |
- Burvall, Anna, et al.
(författare)
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Communication modes in axicon imaging
- 2004
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Ingår i: Riao/Optilas 2004: 5th Iberoamerican Meeting On Optics And 8th Latin American Meeting On Optics, Lasers, And Their Applications, Pts 1-3: Ico Regional Meeting. - : SPIE. - 081945575X ; , s. 1133-1137
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Konferensbidrag (refereegranskat)abstract
- The communication modes are an increasingly frequently used technique for studying the radiation, propagation, and scattering of light. The method is unusual in the way that it gives the information content and the resolution of the fields. It also allows for the possibility of including the noise considerations in the calculations. We present a brief summary of the communication modes method, together with our latest contribution: the communication modes for the axicon geometry.
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| 5. |
- Burvall, Anna, et al.
(författare)
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Communication modes in large-aperture approximation
- 2007
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 32:6, s. 611-613
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Tidskriftsartikel (refereegranskat)abstract
- Simplified versions of the communication modes in the Fresnel domain are derived when the system apertures are large. The approximate modes, which are in the form of spherical waves and sinc functions with a spherical curvature, give physical insight into the communication modes approach and the basic limits of free-space optical communication systems. They also show that Gabor's information theory is readily derived from the communication modes.
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| 6. |
- Burvall, Anna, 1976-, et al.
(författare)
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Diffraction analysis of lens axicons
- 2005
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Ingår i: Diffractive Optics 2005. - : European Optical Society. ; , s. 1-2
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Axicons, as shown in Fig. 1(a), are optical elements that produce long and narrow focallines along the optical axis, rather than the conventional focal point created by a lens. Thefocal line can be used for e.g. alignment, extending the focal depth of existing methods, orparticle trapping and transportation. Axicons are mainly produced as refractive glass cones,or as di®ractive gratings consisting of concentric circles. They can also be constructed fromordinary lenses or lens systems, referred to as lens axicons. There are several lens axicondesigns, using spherical or aspheric surfaces to produce the necessary amount of sphericalaberration.
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| 7. |
- Burvall, Anna, 1976-, et al.
(författare)
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Elementary functions : Propagation of partially coherent light
- 2009
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Ingår i: Journal of the Optical Society of America A. - : Optical Society of America. - 0740-3232. ; 26:7, s. 1721-1729
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Tidskriftsartikel (refereegranskat)abstract
- The theory of propagation of partially coherent light is well known, but performing numerical calculations still presents a difficulty because of the dimensionality of the problem. We propose using a recently introduced method based on the use of elementary functions [Wald et al. Proc. SPIE6040, 59621G (2005)] to reduce the integrals to two dimensions. We formalize the method, describe its inherent assumptions and approximations, and introduce a sampling criterion for adequate interpolation. We present an analysis of some special cases, such as the Gaussian Schell-model beam, and briefly discuss generalized numerical propagation of two-dimensional field distributions.
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| 8. |
- Burvall, Anna, 1976-, et al.
(författare)
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Lens axicons in oblique illumination
- 2007
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 46:3, s. 312-318
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Tidskriftsartikel (refereegranskat)abstract
- Lens axicons, i.e., lenses or lens systems designed to work like axicons, can be a simple and inexpensive way of generating the characteristic axicon focal line. In the design of most lens axicons, only on-axis properties have been considered. We present the design of a lens axicon with improved off-axis characteristics. It is constructed from a singlet lens but with a double-pass feature that allows for a line of uniform width and a stop positioned to minimize aberrations. We perform off-axis analysis and experiments for this system and for another lens axicon, one designed for its on-axis characteristics. We conclude that the off-axis performance of the double-pass axicon is better than both that of an ordinary cone axicon and that of the other lens axicon.
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| 9. |
- Burvall, Anna, 1976-, et al.
(författare)
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Linearity of the pyramid wavefront sensor
- 2006
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 14:25, s. 11925-11934
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Tidskriftsartikel (refereegranskat)abstract
- The pyramid wavefront sensor is very similar to the Fourier knife-edge test, but employs dynamic modulation to quantify the phase derivative. For circular modulation, we compare approximate geometrical optics calculations, more exact diffraction calculations, and experimental results. We show that both the sinusoidal and the approximate linear relationship between wavefront derivative and wavefront sensor response can be derived rigorously from diffraction theory. We also show that geometrical, diffraction and experimental results are very similar, and conclude that the approximate geometrical predictions can be used in place of the more complex diffraction results.
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| 10. |
- Burvall, Anna, et al.
(författare)
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Phase retrieval in X-ray phase-contrast imaging suitable for tomography
- 2011
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Ingår i: Optics Express. - 1094-4087. ; 19:11, s. 10359-10376
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Tidskriftsartikel (refereegranskat)abstract
- In-line phase-contrast X-ray imaging provides images where both absorption and refraction contribute. For quantitative analysis of these images, the phase needs to be retrieved numerically. There are many phase-retrieval methods available. Those suitable for phase-contrast tomography, i.e., non-iterative phase-retrieval methods that use only one image at each projection angle, all follow the same pattern though derived in different ways. We outline this pattern and use it to compare the methods to each other, considering only phase-retrieval performance and not the additional effects of tomographic reconstruction. We also outline derivations, approximations and assumptions, and show which methods are similar or identical and how they relate to each other. A simple scheme for choosing reconstruction method is presented, and numerical phase-retrieval performed for all methods.
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| 11. |
- Burvall, Anna, et al.
(författare)
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Phase-retrieval methods with applications in composite-material tomography
- 2013
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Ingår i: 11th International Conference On X-Ray Microscopy (XRM2012). - : Institute of Physics Publishing (IOPP). ; , s. 012015-
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Konferensbidrag (refereegranskat)abstract
- In-line phase-contrast x-ray imaging is emerging as a method for observing small details when the contrast in absorption x-ray imaging is low. It gives images with strong edge enhancement, and phase retrieval is necessary to obtain quantitative thickness information. In particular for tomography, clarity can be enhanced by phase retrieval, as here demonstrated on a 3D-weave reinforced composite material. Seven suitable phase-retrieval methods are identified and integrated into a single method, where each version is marked by variations in particular steps. The general method and its variations are outlined and a comparison shows which methods are most suitable in different situations.
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| 12. |
- Burvall, Anna, et al.
(författare)
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Simple lens axicon
- 2004
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 43:25, s. 4838-4844
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Tidskriftsartikel (refereegranskat)abstract
- We present the design of a cemented doublet-lens axicon made from spherical surfaces only. Compared with diffractive axicons, refractive cone axicons, and earlier lens axicons with aspheric surfaces, this element is inexpensive and easy to manufacture even with large apertures. The lens axicon is based on the deliberate use of the spherical aberration of the surfaces. The design principles of the element and its characterization, numerically and experimentally, are presented in detail. Although performance was traded for simplicity and robustness, the results show that the lens axicon has the main axicon properties: a narrow, extended line focus of relatively constant width.
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| 13. |
- Burvall, Anna, 1976-, et al.
(författare)
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Singular-value decomposition for through-focus imaging systems
- 2006
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 23:10, s. 2440-2448
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Tidskriftsartikel (refereegranskat)abstract
- Singular-value decomposition (SVD) of a linear imaging system gives information on the null and measurement components of object and image and provides a method for object reconstruction from image data. We apply SVD to through-focus imaging systems that produce several two-dimensional images of a three-dimensional object. Analytical expressions for the singular functions are derived in the geometrical approximation for a telecentric, laterally shift-invariant system linear in intensity. The modes are evaluated numerically, and their accuracy confirmed. Similarly, the modes are derived and evaluated for a continuous image representing the limit of a large number of image planes.
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| 14. |
- Burvall, Anna, et al.
(författare)
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Singular-value decomposition of a tomosynthesis system
- 2010
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Ingår i: Optics Express. - 1094-4087. ; 18:20, s. 20699-20711
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Tidskriftsartikel (refereegranskat)abstract
- Tomosynthesis is an emerging technique with potential to replace mammography, since it gives 3D information at a relatively small increase in dose and cost. We present an analytical singular-value decomposition of a tomosynthesis system, which provides the measurement component of any given object. The method is demonstrated on an example object. The measurement component can be used as a reconstruction of the object, and can also be utilized in future observer studies of tomosynthesis image quality.
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| 15. |
- Burvall, Anna, 1976-, et al.
(författare)
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Singular-value decomposition of axial systems
- 2006
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Ingår i: ICO Topical meeting on optoinformation/Information Photonics 2006.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A method for reconstruction of 3D objects from 2D images, used e.g. in fluorescence microscopy, is takingseveral images along the axial direction. Singular-value decomposition is used to perform the reconstructionand determine its limits.
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| 16. |
- Burvall, Anna, 1976-, et al.
(författare)
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Telephoto axicon
- 2005
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Ingår i: Proceedings of SPIE. - : SPIE - International Society for Optical Engineering.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The axicon is an optical element which creates a narrow focal line along the optical axis, unlike the single focal point produced by a lens. The long and precisely defined axicon focal line is used e.g. in alignment, or to extend the depth of focus of existing methods such as optical coherence tomography or light sectioning. Axicons are generally manufactured as refractive cones or diffractive circular gratings. They are also made as lens systems or doublet lenses, which are easier to produce. We present a design in the form of a reflective-refractive single-element device with annular aperture. This very compact system has only two surfaces, which can be spherical or aspheric depending on the quality required of the focal line. Both surfaces have reflective coatings at specific zones, providing an annular beam suitable for generating extended focal lines. One draw-back of a normal axicon is its sensitivity to the angle of illumination. Even for relatively small angles, astigmatism will broaden the focus and give it an asteroid shape. For our design, with spherical surfaces concentric about the center of the entrance pupil, the focal line remains unchanged in off-axis illumination.
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| 17. |
- Burvall, Anna, et al.
(författare)
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X-ray in-line phase retrieval for tomography
- 2012
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE - International Society for Optical Engineering. - 9780819489623 ; , s. 83136A-
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Konferensbidrag (refereegranskat)abstract
- Phase contrast in X-ray imaging offers imaging of fine features at lower doses than absorption. Of the phasecontrast methods in use in-line phase contrast is interesting due to its experimental simplicity, but to extract information on absorption and phase distributions from the resulting images, phase retrieval is needed. Many phase-retrieval methods suitable for different situations have been developed, but few comparisons of those methods done. We consider a sub-group of phase-retrieval methods that are suitable for tomography, i.e., that use only one exposure (for practical experimental reasons) and are non-iterative (for speed). In total we have found seven suitable methods in the literature. All, though derived in different ways under different assumptions, follow the same pattern and can be outlined as a single method where each specific version is marked by variations in particular steps. We summarize this unified approach, and give the variations of the individual methods. In addition, we outline approximations and assumptions of each method. Using this approach it is possible to conclude which specific algorithms are most suitable in specific situations and to test this based on simulated and experimental data. Ultimately, this leads to conclusions on which methods are the most suitable in different situations.
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| 18. |
- Goncharov, Alexander, et al.
(författare)
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Systematic design of anastigmatic lens axicon
- 2007
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 46:24, s. 6076-6080
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Tidskriftsartikel (refereegranskat)abstract
- We present an analytical method for systematic optical design of a double-pass axicon that shows almost no astigmatism in oblique illumination compared to a conventional linear axicon. The anastigmatic axicon is a singlet lens with nearly concentric spherical surfaces applied in double pass, making it possible to form a long narrow focal line of uniform width. The front and the back surfaces have reflective coatings in the central and annular zones, respectively, to provide the double pass. Our design method finds the radii of curvatures and axial thickness of the lens for a given angle between the exiting rays and the optical axis. It also finds the optimal position of the reflecting zones for minimal vignetting. This method is based on ray tracing of the real rays at the marginal heights of the aperture and therefore is superior to any paraxial method. We illustrate the efficiency of the method by designing a test axicon with optical parameters used for a prototype axicon, which was manufactured and experimentally tested. We compare the optical characteristics of our test axicon with those of the experimental prototype.
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| 19. |
- Hertz, Hans M., et al.
(författare)
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Propagation-based phase-contrast imaging with laboratory sources
- 2016
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Ingår i: Optics InfoBase Conference Papers. - Washington, D.C. : OSA - The Optical Society. - 9781943580095
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Konferensbidrag (refereegranskat)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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| 20. |
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| 21. |
- Häggmark, Ilian, et al.
(författare)
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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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Ingår i: Optics Express. - : The Optical Society. - 1094-4087. ; 25:26, s. 33543-33558
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Tidskriftsartikel (refereegranskat)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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| 22. |
- Häggmark, Ilian
(författare)
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Phase-Contrast X-Ray Imaging of Complex Objects
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 23. |
- Jaroszewicz, Zbigniew, et al.
(författare)
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Axicon : the most important optical element
- 2005
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Ingår i: Optics and photonics news (Print). - : Optical Society of America. - 1047-6938 .- 1541-3721. ; 16:4, s. 34-39
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Tidskriftsartikel (refereegranskat)abstract
- Last year, the optics community celebrated the 50th anniversary of the formal naming of the axicon. Long before that, however, axicons generated vivid discussions and disagreements, often of fundamental importance to our understanding of optics.
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| 24. |
- Jaroszewicz, Zbigniew, et al.
(författare)
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Focal segments obtained by interference of multiple Bessel beams: experimental results
- 2004
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Ingår i: PHOTON MANAGEMENT. - : SPIE. ; , s. 484-489
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the present communicate the experimental results are shown, which deal with the interference pattern created by superposition of multiple Bessel beams. They confirm our earlier results obtained analytically as well as by simulations. The interfering Bessel beams were obtained in a standard way, i.e., a field produced by a set of concentric annular apertures of narrow width illuminated by a plane wave was transformed by a lens into a set of Bessel beams.
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| 25. |
- Jaroszewicz, Z., et al.
(författare)
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Programmable axicon for variable inclination of the focal segment
- 2004
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Ingår i: Journal of Modern Optics. - 0950-0340 .- 1362-3044. ; 51:14, s. 2185-2190
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Tidskriftsartikel (refereegranskat)abstract
- An axicon creates a long and narrow focal segment along its optical axis and therefore it is widely recognized as a cornerstone element in metrology and alignment techniques. In oblique incidence the shape of the axicon can be designed such that its sharp focal line is retained. However, when an elliptical or circular axicon is illuminated at an angle different from the nominal angle, the focal segment suffers from astigmatism and broadens significantly. The use of a spatial light modulator is proposed for real-time compensation of the ensuing aberration. The result is a diffractive axicon with its degree of ellipticity adjusted to the inclination angle of the incident light, thus producing a diffraction-limited Bessel beam for a wide range of illumination angles.
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| 26. |
- Jaroszewicz, Zbigniew, et al.
(författare)
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Spheric long-focal-depth lens : a comment
- 2008
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Ingår i: Optics Communications. - : Elsevier. - 0030-4018 .- 1873-0310. ; 281:19, s. 4849-4850
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Tidskriftsartikel (refereegranskat)
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| 27. |
- Kolacz, Katarzyna, et al.
(författare)
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Present design of lens axicons and their history
- 2007
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Ingår i: Photonics Applications In Astronomy, Communications, Industry, And High-Energy Physics Experiments 2007, Pts 1 And 2. - : SPIE - International Society for Optical Engineering. ; , s. 693740-
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Konferensbidrag (refereegranskat)abstract
- Lens systems designed to work like axicons can be a simple and cheap way of generating focal lines characteristic for these elements. We present two lens axicons made from ordinary lenses with spherical surfaces which take advantage of their inherent spherical aberration for creation of the focal segment. One of them is composed from two lenses with blocked central part. The second one is a single meniscus lens with appropriate reflective coatings. The results show that both new elements exhibit main axicon properties. Additionally the second lens axicon is resistant to astigmatism and maintains good quality of the focal segment even in the case of oblique illumination.
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| 28. |
- Larsson, Daniel H., et al.
(författare)
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A 24 keV liquid-metal-jet x-ray source for biomedical applications
- 2011
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 82:12, s. 123701-
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Tidskriftsartikel (refereegranskat)abstract
- We present a high-brightness 24-keV electron-impact microfocus x-ray source based on continuous operation of a heated liquid-indium/gallium-jet anode. The 30–70 W electron beam is magnetically focused onto the jet, producing a circular 7–13 μm full width half maximum x-ray spot. The measured spectral brightness at the 24.2 keV In Kα line is 3 × 109 photons/(s × mm2 × mrad2 × 0.1% BW) at 30 W electron-beam power. The high photon energy compared to existing liquid-metal-jet sources increases the penetration depth and allows imaging of thicker samples. The applicability of the source in the biomedical field is demonstrated by high-resolution imaging of a mammography phantom and a phase-contrast angiography phantom.
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| 29. |
- Larsson, Daniel H., et al.
(författare)
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First application of liquid-metal-jet sources for small-animal imaging : High-resolution CT and phase-contrast tumor demarcation
- 2013
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405 .- 2473-4209. ; 40:2, s. 021909-
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Small-animal studies require images with high spatial resolution and high contrast due to the small scale of the structures. X-ray imaging systems for small animals are often limited by the microfocus source. Here, the authors investigate the applicability of liquid-metal-jet x-ray sources for such high-resolution small-animal imaging, both in tomography based on absorption and in soft-tissue tumor imaging based on in-line phase contrast. Methods: The experimental arrangement consists of a liquid-metal-jet x-ray source, the small-animal object on a rotating stage, and an imaging detector. The source-to-object and object-to-detector distances are adjusted for the preferred contrast mechanism. Two different liquid-metal-jet sources are used, one circulating a Ga/In/Sn alloy and the other an In/Ga alloy for higher penetration through thick tissue. Both sources are operated at 40-50 W electron-beam power with similar to 7 mu m x-ray spots, providing high spatial resolution in absorption imaging and high spatial coherence for the phase-contrast imaging. Results: High-resolution absorption imaging is demonstrated on mice with CT, showing 50 mu m bone details in the reconstructed slices. High-resolution phase-contrast soft-tissue imaging shows clear demarcation of mm-sized tumors at much lower dose than is required in absorption. Conclusions: This is the first application of liquid-metal-jet x-ray sources for whole-body small-animal x-ray imaging. In absorption, the method allows high-resolution tomographic skeletal imaging with potential for significantly shorter exposure times due to the power scalability of liquid-metal-jet sources. In phase contrast, the authors use a simple in-line arrangement to show distinct tumor demarcation of few-mm-sized tumors. This is, to their knowledge, the first small-animal tumor visualization with a laboratory phase-contrast system.
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| 30. |
- Larsson, Daniel H., et al.
(författare)
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Small-animal tomography with a liquid-metal-jet x-ray source
- 2012
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE - International Society for Optical Engineering. - 9780819489623 ; , s. 83130N-
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Konferensbidrag (refereegranskat)abstract
- X-ray tomography of small animals is an important tool for medical research. For high-resolution x-ray imaging of few-cm-thick samples such as, e.g., mice, high-brightness x-ray sources with energies in the few-10-keV range are required. In this paper we perform the first small-animal imaging and tomography experiments using liquid-metal-jet-anode x-ray sources. This type of source shows promise to increase the brightness of microfocus x-ray systems, but present sources are typically optimized for an energy of 9 keV. Here we describe the details of a high-brightness 24-keV electron-impact laboratory microfocus x-ray source based on continuous operation of a heated liquid-In/Ga-jet anode. The source normally operates with 40 W of electron-beam power focused onto the metal jet, producing a 7×7 μm 2 FWHM x-ray spot. The peak spectral brightness is 4 × 10 9 photons/( s × mm 2 × mrad 2 × 0.1%BW) at the 24.2 keV In K α line. We use the new In/Ga source and an existing Ga/In/Sn source for high-resolution imaging and tomography of mice.
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| 31. |
- Larsson, Daniel, 1985-
(författare)
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Small-Animal Imaging with Liquid-Metal-Jet X-Ray Sources
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 32. |
- Larsson, Jakob C.
(författare)
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Laboratory x-ray fluorescence tomography
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 33. |
- Lundström, Ulf, 1986-
(författare)
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Phase-Contrast X-Ray Carbon Dioxide Angiography
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phase-contrast x-ray imaging is an emerging technology, which allows for imaging of smaller features than conventional absorption-based x-ray imaging, with lower radiation dose. Instead of the attenuation that is normally used in x-ray imaging, it utilizes the phase shift introduced by an object to the transmitted x-rays. This phase shift can change the directions of the x-rays slightly, which can be measured in a few different ways. Propagation-based phase contrast, which is the method most used in this Thesis, detects these deviations using a high-resolution imaging detector at a distance from the sample. This Thesis describes how phase-contrast x-ray imaging can be used to image the internal structures of small animals like mice and rats. A technique for imaging of very small blood vessels has been developed and analyzed. By injecting a gas, such as carbon dioxide, into the vascular system, blood vessels down to 8 µm in diameter have been visualized. This is considerably smaller than the 50 µm vessels that can be imaged using iodine-based contrast agents at radiation doses compatible with living animals. A recently invented type of x-ray source, based on a jet of liquid metal as electron-beam target, has been used and further developed for the imaging purposes of this Thesis. Such metal-jet x-ray sources provide very high x-ray flux for the small x-ray spot sizes at which they operate, something that has been crucial for the quality of the phase-contrast images acquired.
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| 34. |
- Lundström, Ulf, et al.
(författare)
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Small-Animal microangiography using phase-contrast X-ray imaging and gas as contrast agent
- 2014
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Ingår i: Medical Imaging 2014. - : SPIE - International Society for Optical Engineering. - 9780819498267 ; , s. 90331L-
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Konferensbidrag (refereegranskat)abstract
- We use propagation-based phase-contrast X-ray imaging with gas as contrast agent To visualize The microvasculature in small animals like mice and rats. The radiation dose required for absorption X-ray imaging is proportional To The minus fourth power of The structure size To be detected. This makes small vessels impossible To image at reasonable radiation doses using The absorption of conventional iodinated contrast agents. Propagation-based phase contrast gives enhanced contrast for high spatial frequencies by moving The detector away from The sample To let phase variations in The Transmitted X-rays develop into intensity variations at The detector. Blood vessels are normally difficult To observe in phase contrast even with iodinated contrast agents as The density difference between blood and most Tissues is relatively small. By injecting gas into The blood stream This density difference can be greatly enhanced giving strong phase contrast. One possible gas To use is carbon dioxide, which is a clinically accepted X-ray contrast agent. The gas is injected into The blood stream of patients To Temporarily displace The blood in a region and Thereby reduce The X-ray absorption in The blood vessels. We have shown That This method can be used To image blood vessels down To 8 μm in diameter in mouse ears. The low dose requirements of This method indicate a potential for live small-Animal imaging and longitudinal studies of angiogenesis.
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| 35. |
- Lundström, Ulf, et al.
(författare)
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X-ray phase contrast angiography using CO 2 as contrast agent
- 2012
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE - International Society for Optical Engineering. - 9780819489623 ; , s. 83135J-
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Konferensbidrag (refereegranskat)abstract
- We investigate the possibility of using x-ray in-line phase-contrast imaging with gaseous carbon dioxide as contrast agent to visualize small blood vessels. These are difficult to image at reasonable radiation doses using the absorption of conventional iodinated contrast agents. In-line phase contrast is a method for retrieving information on the electron density of the sample as well as the absorption, by moving the detector away from the sample to let phase variations in the transmitted x-rays develop into intensity variations at the detector. Blood vessels are normally difficult to observe in phase contrast even with iodinated contrast agents as the density difference compared to most tissues is small. Carbon dioxide is a clinically accepted x-ray contrast agent. The gas is injected into the blood stream of patients to temporarily displace the blood in a region and thereby reduce the x-ray absorption in the blood vessels. This gives a large density difference which is ideal for phase-contrast imaging. We demonstrate the possibilities of the method by imaging the arterial system of a rat kidney injected with carbon dioxide. Vessels down to 23 ÎŒm in diameter are shown. The method shows potential for live small-animal imaging.
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| 36. |
- Lundström, Ulf, et al.
(författare)
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X-ray phase-contrast CO2 angiography for sub-10 mu m vessel imaging
- 2012
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 57:22, s. 7431-7441
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Tidskriftsartikel (refereegranskat)abstract
- X-ray in-line phase contrast has recently been combined with CO2 angiography for high-resolution small-animal vascular imaging at low radiation dose. In this paper we further investigate the potential and limitations of this method and demonstrate observation of vessels down to 8 mu m in diameter, considerably smaller than the 60 mu m previously reported. Our in-line phase-contrast imaging system is based on a liquid-metal-jet-anode x-ray source and utilizes free-space propagation to convert phase shifts, caused by refractive index variations, into intensity differences. Enhanced refractive index variations are obtained through injection of CO2 gas into the vascular system to replace the blood. We show rat-kidney images with blood vessels down to 27 mu m in diameter and mouse-ear images with vessels down to 8 mu m. The minimum size of observable blood vessels is found to be limited by the penetration of gas into the vascular system and the signal-to-noise ratio, i.e. the allowed dose. The diameters of vessels being gas-filled depend on the gas pressure and follow a simple model based on surface tension. A theoretical signal-to-noise comparison shows that this method requires 1000 times less radiation dose than conventional iodine-based absorption contrast for observing sub-50 mu m vessels.
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| 37. |
- Lundström, Ulf, et al.
(författare)
-
X-ray phase contrast for CO2 microangiography
- 2012
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 57:9, s. 2603-2617
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a laboratory method for imaging small blood vessels using x-ray propagation-based phase-contrast imaging and carbon dioxide (CO2) gas as a contrast agent. The limited radiation dose in combination with CO2 being clinically acceptable makes the method promising for small-diameter vascular visualization. We investigate the possibilities and limitations of the method for small-animal angiography and compare it with conventional absorption-based x-ray angiography. Photon noise in absorption-contrast imaging prevents visualization of blood vessels narrower than 50 mu m at the highest radiation doses compatible with living animals, whereas our simulations and experiments indicate the possibility of visualizing 20 mu m vessels at radiation doses as low as 100 mGy. Experimental computed tomography of excised rat kidney shows blood vessels of diameters down to 60 mu m with improved image quality compared to absorption-based methods. With our present prototype x-ray source, the acquisition time for a tomographic dataset is approximately 1 h, which is long compared to the 1-20 min common for absorption-contrast micro-CT systems. Further development of the liquid-metal-jet microfocus x-ray sources used here and high-resolution x-ray detectors shows promise to reduce exposure times and make this high-resolution method practical for imaging of living animals.
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| 38. |
- Lundström, Ulf, et al.
(författare)
-
X-ray phase contrast with injected gas for tumor microangiography
- 2014
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 59:11, s. 2801-2811
-
Tidskriftsartikel (refereegranskat)abstract
- We show that the microvasculature of mouse tumors can be visualized using propagation-based phase-contrast x-ray imaging with gas as the contrast agent. The large density difference over the gas-tissue interface provides high contrast, allowing the imaging of small-diameter blood vessels with relatively short exposure times and low dose using a compact liquid-metal-jet x-ray source. The method investigated is applied to tumors (E1A/Ras-transformed mouse embryonic fibroblasts) grown in mouse ears, demonstrating sub-15-mu m-diameter imaging of their blood vessels. The exposure time for a 2D projection image is a few seconds and a full tomographic 3D map takes some minutes. The method relies on the strength of the vasculature to withstand the gas pressure. Given that tumor vessels are known to be more fragile than normal vessels, we investigate the tolerance of the vasculature of 12 tumors to gas injection and find that a majority withstand 200 mbar pressures, enough to fill 12-mu m-diameter vessels with gas. A comparison of the elasticity of tumorous and non-tumorous vessels supports the assumption of tumor vessels being more fragile. Finally, we conclude that the method has the potential to be extended to the imaging of 15 mu m vessels in thick tissue, including mouse imaging, making it of interest for, e.g., angiogenesis research.
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| 39. |
- Martinsson, Per, 1971-, et al.
(författare)
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Communication modes in scalar diffraction
- 2008
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Ingår i: Optik (Stuttgart). - : Elsevier BV. - 0030-4026 .- 1618-1336. ; 119:3, s. 103-111
-
Tidskriftsartikel (refereegranskat)abstract
- The communication modes are a useful concept in studies of optical resolution, wave propagation, and image synthesis. We present an overview of earlier results on the communication modes in scalar diffraction theory. Besides the general theory, the modes are reviewed for the far-field and Fresnel regimes, and new eigenequations are derived for wide-angle diffraction. We prove a conjugate relationship between the transmitting and receiving modes in a general symmetric system. We also suggest an approximate method for far-field and Fresnel domain propagation, in which propagation amounts to a rotation of each mode in the complex plane. The main focus is on the near-field communication modes, where we present numerical examples of the modes and coupling strengths for a near-field geometry with a sub-wavelength size receiving domain. These results provide insights, for example, into the understanding of near-field scanning probe techniques.
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| 40. |
- Reza, Salim, 1985-
(författare)
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Phase-Contrast and Spectroscopic X-ray Imaging for Paperboard Quality Assurance
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The end-use performance of a paperboard depends on its quality.The major properties of a good quality paperboard include consistencyin the expected ratio between the thickness of the core andthe coating layers, and the uniformity in the coating layer. Measurementsystems using X-rays to monitor these properties could assistthe paperboard industries to assure the quality of their products in anon-destructive and automatic manner. Phase Contrast X-ray Imaging (PCXI) has been used successfullyto look inside a wide range of objects using synchrotron radiationsources. Recent advancements in the grating interferometer basedPCXI technique enables high quality phase-contrast and dark-fieldimages to be obtained using conventional X-ray tubes. The darkfieldimages map the scattering inhomogeneities inside objects andis very sensitive to micro-structures, and thus, can reveal useful informationabout the object’s inner structures, such as, the fibre structuresinside paperboards. In this thesis, methods, using spectroscopic X-ray imaging andPCXI technique have been demonstrated to measure paperboard quality.The thicknesses of the core and the coating layers on a paperboardwith the coating layer on only one side can be measured usingspectroscopic X-ray imaging technique. However, the limitedspectral and spatial resolution offered by the measurement systembeing used led to the measured thicknesses of the layers being lowerthan their actual thicknesses in the paperboard sample. Suggestionshave been made in relation to overcoming these limitations and toenhance the performance of the method. The dark-field signals from paperboard samples with different qualityindices are analysed. The isotropic and the anisotropic scatteringcoefficients for all of the samples have been calculated. Basedon the correlation between the isotropic coefficients and the qualityindices of the paperboards, suggestions have been made for paperboardquality measurements.
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| 41. |
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| 42. |
- Rezasson, Reza, 1985-, et al.
(författare)
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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
-
Ingår i: TAPPI Journal. - : TAPPI. - 0734-1415. ; 22:2, s. 99-106
-
Tidskriftsartikel (refereegranskat)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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| 43. |
- Romell, Jenny, et al.
(författare)
-
Comparison of laboratory grating-based and speckle-tracking x-ray phase-contrast imaging
- 2017
-
Ingår i: X-Ray Microscopy Conference 2016 (XRM 2016)15–19 August 2016, Oxford University, United Kingdom. - : Institute of Physics Publishing (IOPP).
-
Konferensbidrag (refereegranskat)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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| 44. |
- Romell, Jenny
(författare)
-
Virtual histology by laboratory x-ray phase-contrast tomography
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 45. |
- Shaker, Kian
(författare)
-
Preclinical X-ray imaging beyond attenuation contrast
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 46. |
- Smith, Arlene, et al.
(författare)
-
Numerical partially coherent imaging using elementary functions
- 2008
-
Ingår i: OPTICAL DESIGN AND ENGINEERING III, PTS 1 AND 2. - : SPIE - International Society for Optical Engineering. - 9780819473301
-
Konferensbidrag (refereegranskat)abstract
- The theory of coherence and propagation of light through imaging systems is well established. For coherent and incoherent sources, the intensity in the image plane can be predicted numerically using a straightforward convolution calculation. Image formation becomes more complicated when dealing with partially coherent light, as treating two-dimensional intensity fields (described by the four-dimensional mutual coherence function in the time domain or the cross-spectral density in the frequency domain) requires evaluating four-dimensional integrals. Thus, calculations are complex, slow to process and place demands on system memory. We present a variation of a method recently introduced [Wald et al, Proc SPIE, 59621G, 2005], in which elementary functions are used to reduce the integrals to two dimensions for light of relatively high degree of coherence. The method resembles the coherent-mode expansion, but the elementary functions are easier to find and work with than the coherent modes. We outline the method and present some numerical results. This approach has applications in modelling of photolithographic systems in which partially coherent excimer lasers operating in the Deep Ultra-Violet (DUV) regime have been used for the last decade. An accurate numerical model of such systems could prove useful in solving the classic inverse imaging problem of lithography reticle design.
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| 47. |
- Smith, Arlene, et al.
(författare)
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Partial spatial coherence in an excimer-laser lithographic imaging system
- 2010
-
Ingår i: Optical microlithography XXIII. - : SPIE - International Society for Optical Engineering. - 9780819480545
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Konferensbidrag (refereegranskat)abstract
- We have recently explored the Elementary Function method, previously presented by Wald et al (Proc. SPIE 59621G, 2005), and we have demonstrated under what circumstances this method can be used to reduce the propagation calculations of partially coherent light to two dimensions. In this paper, we examine the methods used to measure the spatial coherence of a light source in the literature. We present a method based on work previously shown by Mejia et al (Opt Comm 273 (428-434), 2007) which uses an array of pinholes with one degree of redundancy. We discuss the design of the pinhole array and present the results of some simulations.
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| 48. |
- Smith, Arlene, et al.
(författare)
-
Partially coherent image computation using elementary functions
- 2009
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Ingår i: Optical Microlithography XXII. - : SPIE - International Society for Optical Engineering. - 9780819475275
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It is well-known that calculations of the propagation of partially coherent light, such as those required for the calculation of two-dimensional image intensities, involve four-dimensional functions. Recently, Wald et al [Proc SPIE, 59621G, 2005] outlined a method for reducing the four-dimensional problem to a purely twodimensional one. Instead of an exact modal expansion of the mutual coherence function or cross-spectral density, an approximate expansion is used, into what we call elementary functions. In this paper, rules of thumb are developed for fast and efficient computation of the image intensity in a simple partially coherent lithographic imaging system.
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| 49. |
- Thuering, T., et al.
(författare)
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X-ray grating interferometry with a liquid-metal-jet source
- 2013
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:9, s. 091105-
-
Tidskriftsartikel (refereegranskat)abstract
- A liquid-metal-jet X-ray tube is used in an X-ray phase-contrast microscope based on a Talbot type grating interferometer. With a focal spot size in the range of a few microns and a photon flux of similar to 10(12) photons/s x sr, the brightness of such a source is approximately one order of magnitude higher than for a conventional microfocus source. For comparison, a standard microfocus source was used with the same grating interferometer, showing significantly increased visibility for the liquid-metal-jet arrangement. Together with the increased flux, this results in improved signal-to-noise ratio.
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| 50. |
- Twengström, William
(författare)
-
High-resolution biomedical phase-contrast tomography
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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