| 1. |
- Velroyen, A, et al.
(författare)
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Grating-based X-ray Dark-field Computed Tomography of Living Mice.
- 2015
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Ingår i: EBioMedicine. - : Elsevier BV. - 2352-3964. ; 2:10, s. 1500-1506
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Tidskriftsartikel (refereegranskat)abstract
- Changes in x-ray attenuating tissue caused by lung disorders like emphysema or fibrosis are subtle and thus only resolved by high-resolution computed tomography (CT). The structural reorganization, however, is of strong influence for lung function. Dark-field CT (DFCT), based on small-angle scattering of x-rays, reveals such structural changes even at resolutions coarser than the pulmonary network and thus provides access to their anatomical distribution. In this proof-of-concept study we present x-ray in vivo DFCTs of lungs of a healthy, an emphysematous and a fibrotic mouse. The tomographies show excellent depiction of the distribution of structural - and thus indirectly functional - changes in lung parenchyma, on single-modality slices in dark field as well as on multimodal fusion images. Therefore, we anticipate numerous applications of DFCT in diagnostic lung imaging. We introduce a scatter-based Hounsfield Unit (sHU) scale to facilitate comparability of scans. In this newly defined sHU scale, the pathophysiological changes by emphysema and fibrosis cause a shift towards lower numbers, compared to healthy lung tissue.
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| 2. |
- Yaroshenko, A., et al.
(författare)
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Preclinical x-ray dark-field radiography for pulmonary emphysema evaluation
- 2013
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Ingår i: ISBI 2013 - 2013 IEEE 10th International Symposium on Biomedical Imaging : From Nano to Macro - From Nano to Macro. - 1945-7928 .- 1945-8452. - 9781467364553 - 9781467364560 ; , s. 370-373
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Konferensbidrag (refereegranskat)abstract
- Pulmonary emphysema is a widespread disorder characterized by irreversible destruction of alveolar walls. The spatial distribution of the disease, so far, could only be obtained using an x-ray CT scan, implying a high patient dose. X-ray scattering on alveolar structures is measured in the dark-field signal. The signal is dependent on the size of alveoli and therefore, a combination of absorption and dark-field signal is explored for mapping the distribution of emphysema in the lung on x-ray projection images. In this study three excised murine lungs with pulmonary emphysema and three control samples were imaged using a compact, cone-beam, small-animal x-ray dark-field scanner with a polychromatic source. Statistical analysis of the results, based on a combination of transmission and dark-field signals, revealed a distinct difference between emphysematous and control samples. Subsequently, the distribution of emphysema was mapped out per-pixel for the lungs and showed good agreement with histological findings.
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| 3. |
- Bech, Martin, et al.
(författare)
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In-vivo dark-field and phase-contrast x-ray imaging.
- 2013
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3:Nov 13
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Tidskriftsartikel (refereegranskat)abstract
- Novel radiography approaches based on the wave nature of x-rays when propagating through matter have a great potential for improved future x-ray diagnostics in the clinics. Here, we present a significant milestone in this imaging method: in-vivo multi-contrast x-ray imaging of a mouse using a compact scanner. Of particular interest is the enhanced contrast in regions related to the respiratory system, indicating a possible application in diagnosis of lung diseases (e.g. emphysema).
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| 4. |
- Velroyen, A., et al.
(författare)
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Microbubbles as a scattering contrast agent for grating-based x-ray dark-field imaging
- 2013
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Ingår i: Physics in Medicine and Biology. - 1361-6560. ; 58:4, s. 37-46
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Tidskriftsartikel (refereegranskat)abstract
- In clinically established-absorption-based-biomedical x-ray imaging, contrast agents with high atomic numbers (e.g. iodine) are commonly used for contrast enhancement. The development of novel x-ray contrast modalities such as phase contrast and dark-field contrast opens up the possible use of alternative contrast media in x-ray imaging. We investigate using ultrasound contrast agents, which unlike iodine-based contrast agents can also be administered to patients with renal impairment and thyroid dysfunction, for application with a recently developed novel x-ray dark-field imaging modality. To produce contrast from these microbubble-based contrast agents, our method exploits ultra-small-angle coherent x-ray scattering. Such scattering dark-field x-ray images can be obtained with a grating-based x-ray imaging setup, together with refraction-based differential phase-contrast and the conventional attenuation contrast images. In this work we specifically show that ultrasound contrast agents based on microbubbles can be used to produce strongly enhanced dark-field contrast, with superior contrast-to-noise ratio compared to the attenuation signal. We also demonstrate that this method works well with an x-ray tube-based setup and that the relative contrast gain even increases when the pixel size is increased from tenths of microns to clinically compatible detector resolutions about up to a millimetre.
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| 5. |
- Khrapak, S. A., et al.
(författare)
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Particle charge in the bulk of gas discharges
- 2005
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Ingår i: Physical Review E. - 1539-3755. ; 72:1
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Tidskriftsartikel (refereegranskat)abstract
- An experimental determination of particle charge in a bulk dc discharge plasma covering a wide range of neutral gas pressures, was recently reported [S. Ratynskaia , Phys. Rev. Lett. 93, 085001 (2004)]. The charges obtained were several times smaller than the predictions of collisionless orbital motion limited theory. This discrepancy was attributed to the effect of ion-neutral collisions. In the present paper a more detailed description of this experiment is provided and additional experimental results obtained with particles of different sizes are reported. The measurements are compared with molecular dynamics simulations of particle charging for conditions similar to those of the experiment, with other available experimental data on particle charge in the bulk of gas discharges, and with a simple analytical model accounting for ion-neutral collisions. All the considered evidence indicates that ion-neutral collisions represent a very important factor, which significantly affects (reduces) the particle charge under typical discharge conditions.
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| 6. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Experimental determination of dust-particle charge in a discharge plasma at elevated pressures
- 2004
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:8
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Tidskriftsartikel (refereegranskat)abstract
- The charge of dust particles is determined experimentally in a bulk dc discharge plasma in the pressure range 20-100 Pa. The charge is obtained by two independent methods: one based on an analysis of the particle motion in a stable particle flow and another on an analysis of the transition of the flow to an unstable regime. Molecular-dynamics simulations of the particle charging for conditions similar to those of the experiment are also performed. The results of both experimental methods and the simulations demonstrate good agreement. The charge obtained is several times smaller than predicted by the collisionless orbital motion theory, and thus the results serve as an experimental indication that ion-neutral collisions significantly affect particle charging.
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| 7. |
- Thoma, Markus H., et al.
(författare)
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PK-4 : Complex plasmas in space - The next generation
- 2007
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 35:2, s. 255-259
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Tidskriftsartikel (refereegranskat)abstract
- PK-4 is an experiment designed to investigate complex plasmas in a combined dc/RF discharge under microgravity conditions on board of the International Space Station. The dc,discharge is produced in a glass tube with a length of 35 cm and, a diameter of 3 cm. In addition, an RF discharge can be applied by external RF coils. The setup is especially suited for studying the liquid phase of the complex plasmas, e.g., flow phenomena such as turbulence or nozzles, and forces acting on the microparticles. Experiments in the laboratory and in parabolic flights have been used to determine the charge of the microparticles as well as the ion drag force acting on them.
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| 8. |
- Yaroshenko, V., et al.
(författare)
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Determination of the ion-drag force in a complex plasma
- 2005
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- The ion-drag force acting on dust particles in the positive column of a dc discharge is measured in the pressure range of 20-120 Pa. The force is obtained by a method which does not require a priori knowledge of the particle charge, but uses the charge gradient determined from the same experiment. The method depends only on two experimentally determined quantities: the particle drift velocity and the electric field. The comparison of experimental results with theoretical models is presented and discussed.
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| 9. |
- Yaroshenko, V.V., et al.
(författare)
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Characteristics of charged dust inferred from the Cassini RPWS measurements in the vicinity of Enceladus
- 2009
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 57:14-15, s. 1807-1812
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Tidskriftsartikel (refereegranskat)abstract
- The data obtained by the Cassini Radio and Plasma Wave Science (RPWS) instrument during the shallow (17.02.2005) and the steep (14.07.2005) crossings of the E-ring revealed a considerable electron depletion in proximity to Enceladus's orbit (the difference between the ion and electron densities can reach similar to 70 cm(-3)). Assuming that this depletion is a signature of the presence of charged dust particles, the main characteristics of dust down to submicron sized particles are derived. The differential size distribution is found to be well described by a power law with an index mu similar to 5.5-6 for the lower size limit a(min) = 0.03 mu m and mu similar to 7.3-8 for a(min) = 0.1 mu m. The calculated average integral dust number density is weakly affected by values of mu and a(min). For a greater than or similar to 0.1 mu m, both flybys gave the maximum dust density about 0.1-0.3 cm(-3) in the vicinity of Enceladus. Our results imply that the dust structure near Enceladus is characterized by approximately the same vertical length scale of 8000 km and reaches a maximum at the same radial distance (displaced outward of the orbit of Enceladus) as found by Kempf et al. [2008. The E-ring in the vicinity of Enceladus. Spatial distribution and properties of the ring particles. Icarus 193, 420-437], from the dust impact data.
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| 10. |
- Yaroshenko, V. V., et al.
(författare)
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Measurements of the dust-ion momentum transfer frequency and ion drag force in complex plasmas
- 2005
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 45:04-mar, s. 223-228
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Tidskriftsartikel (refereegranskat)abstract
- A simple self-consistent method to estimate the effect of the streaming ions on microparticles in a positive column of a dc discharge plasma is presented. The momentum transfer frequency in dust-ion collisions and the ion drag force are determined within a wide range of gas pressures, p = 20 - 120 Pa. The method does not require a priory knowledge of the particle charge, but involves only the particle charge gradient which is recovered from the same experimental data. The method depends only on two experimental quantities: dust particle drift velocity and electric field, thus minimizing the errors in the estimates. Reasonable agreement is found between our force measurements and theoretical predictions, corresponding to the regime of moderate ion-dust particle coupling.
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