| 1. |
- Pearce, Neil E, et al.
(författare)
-
IARC Monographs : 40 Years of Evaluating Carcinogenic Hazards to Humans
- 2015
-
Ingår i: Journal of Environmental Health Perspectives. - : Environmental Health Perspectives. - 0091-6765 .- 1552-9924. ; 123:6, s. 507-514
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Recently the International Agency for Research on Cancer (IARC) Programme for the Evaluation of Carcinogenic Risks to Humans has been criticized for several of its evaluations, and also the approach used to perform these evaluations. Some critics have claimed that IARC Working Groups' failures to recognize study weaknesses and biases of Working Group members have led to inappropriate classification of a number of agents as carcinogenic to humans.OBJECTIVES: The authors of this paper are scientists from various disciplines relevant to the identification and hazard evaluation of human carcinogens. We have examined here criticisms of the IARC classification process to determine the validity of these concerns. We review the history of IARC evaluations and describe how the IARC evaluations are performed.DISCUSSION: We conclude that these recent criticisms are unconvincing. The procedures employed by IARC to assemble Working Groups of scientists from the various discipline and the techniques followed to review the literature and perform hazard assessment of various agents provide a balanced evaluation and an appropriate indication of the weight of the evidence. Some disagreement by individual scientists to some evaluations is not evidence of process failure. The review process has been modified over time and will undoubtedly be altered in the future to improve the process. Any process can in theory be improved, and we would support continued review and improvement of the IARC processes. This does not mean, however, that the current procedures are flawed.CONCLUSIONS: The IARC Monographs have made, and continue to make, major contributions to the scientific underpinning for societal actions to improve the public's health.
|
|
| 2. |
- Zanette, I., et al.
(författare)
-
X-ray microtomography using correlation of near-field speckles for material characterization
- 2015
-
Ingår i: 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
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 3. |
- Fogelqvist, Emelie, et al.
(författare)
-
Stability of liquid-nitrogen-jet laser-plasma targets
- 2015
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 118:17
-
Tidskriftsartikel (refereegranskat)abstract
- Microscopic jets of cryogenic substances such as liquid nitrogen are important regenerative high-density targets for high-repetition rate, high-brightness laser-plasma soft x-ray sources. When operated in vacuum such liquid jets exhibit several non-classical instabilities that negatively influence the x-ray source's spatial and temporal stability, yield, and brightness, parameters that all are important for applications such as water-window microscopy. In the present paper, we investigate liquid-nitrogen jets with a flash-illumination imaging system that allows for a quantitative stability analysis with high spatial and temporal resolution. Direct and indirect consequences of evaporation are identified as the key reasons for the observed instabilities. Operating the jets in an approximately 100 mbar ambient atmosphere counteracts the effects of evaporation and produces highly stable liquid nitrogen jets. For operation in vacuum, which is necessary for the laser plasmas, we improve the stability by introducing an external radiative heating element. The method significantly extends the distance from the nozzle that can be used for liquid-jet laser plasmas, which is of importance for high-average-power applications. Finally, we show that laser-plasma operation with the heating-element-stabilized jet shows improved short-term and long-term temporal stability in its water-window x-ray emission.
|
|
| 4. |
- Hertz, Hans M., et al.
(författare)
-
Propagation-based phase-contrast imaging with laboratory sources
- 2016
-
Ingår i: Optics InfoBase Conference Papers. - Washington, D.C. : OSA - The Optical Society. - 9781943580095
-
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.
|
|
| 5. |
|
|
| 6. |
- Larsson, Jakob C., et al.
(författare)
-
Characterization of scintillator-based detectors for few-ten-keV high-spatial-resolution x-ray imaging
- 2016
-
Ingår i: Medical physics (Lancaster). - : WILEY. - 0094-2405. ; 43:6
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: High-spatial-resolution x-ray imaging in the few-ten-keV range is becoming increasingly important in several applications, such as small-animal imaging and phase-contrast imaging. The detector properties critically influence the quality of such imaging. Here the authors present a quantitative comparison of scintillator-based detectors for this energy range and at high spatial frequencies. Methods: The authors determine the modulation transfer function, noise power spectrum (NPS), and detective quantum efficiency for Gadox, needle CsI, and structured CsI scintillators of different thicknesses and at different photon energies. An extended analysis of the NPS allows for direct measurements of the scintillator effective absorption efficiency and effective light yield as well as providing an alternative method to assess the underlying factors behind the detector properties. Results: There is a substantial difference in performance between the scintillators depending on the imaging task but in general, the CsI based scintillators perform better than the Gadox scintillators. At low energies (16 keV), a thin needle CsI scintillator has the best performance at all frequencies. At higher energies (28-38 keV), the thicker needle CsI scintillators and the structured CsI scintillator all have very good performance. The needle CsI scintillators have higher absorption efficiencies but the structured CsI scintillator has higher resolution. Conclusions: The choice of scintillator is greatly dependent on the imaging task. The presented comparison and methodology will assist the imaging scientist in optimizing their high-resolution few-ten-keV imaging system for best performance.
|
|
| 7. |
- Larsson, Jakob C., et al.
(författare)
-
High-spatial-resolution nanoparticle X-ray fluorescence tomography
- 2016
-
Ingår i: MEDICAL IMAGING 2016. - : SPIE. - 9781510600188
-
Konferensbidrag (refereegranskat)abstract
- X-ray fluorescence tomography (XFCT) has potential for high-resolution 3D molecular x-ray bio-imaging. 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 XFCT systems 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. We have developed a laboratory XFCT system with high spatial resolution (sub-100 mu m), low NP concentration and vastly decreased 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 an energy-resolving photon-counting detector. By using the source's characteristic 24 keV line-emission together with carefully matched molybdenum nanoparticles the Compton background is greatly reduced, increasing the SNR. Each measurement provides information about the spatial distribution and concentration of the Mo nanoparticles. A filtered back-projection method is used to produce the final XFCT image.
|
|
| 8. |
- Li, Yuyang, et al.
(författare)
-
A Library of Potential Nanoparticle Contrast Agents for X-Ray Fluorescence Tomography Bioimaging
- 2018
-
Ingår i: Contrast Media & Molecular Imaging. - : WILEY-HINDAWI. - 1555-4309 .- 1555-4317.
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles (NPs) have been used as contrast agents for several bioimaging modalities. X-ray fluorescence (XRF) tomography can provide sensitive and quantitative 3D detection of NPs. With spectrally matched NPs as contrast agents, we demonstrated earlier in a laboratory system that XRF tomography could achieve high-spatial-resolution tumor imaging in mice. Here, we present the synthesis, characterization, and evaluation of a library of NPs containing Y, Zr, Nb, Rh, and Ru that have spectrally matched K-shell absorption for the laboratory scale X-ray source. The K-shell emissions of these NPs are spectrally well separated from the X-ray probe and the Compton background, making them suitable for the lab-scale XRF tomography system. Their potential as XRF contrast agents is demonstrated successfully in a small-animal equivalent phantom, confirming the simulation results. The diversity in the NP composition provides a flexible platform for a better design and biological optimization of XRF tomography nanoprobes.
|
|
| 9. |
- 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.
|
|
| 10. |
- Romell, Jenny, et al.
(författare)
-
Virtual histology of dried and mummified biological samples by laboratory phase-contrast tomography
- 2019
-
Ingår i: X-Ray Nanoimaging. - : SPIE - The International Society for Optics and Photonics.
-
Konferensbidrag (refereegranskat)abstract
- Ancient remains from humans, animals and plants hold valuable information about our history. X-ray imaging methods are often, because of their non-destructive nature, used in the analysis of such samples. The classical x-ray imaging methods, radiography and computed tomography (CT), are based on absorption, which works well for radiodense structures like bone, but gives limited contrast for textiles and soft tissues, which exhibit high x-ray transmission. Destructive methods, such as classical histology, have historically been used for analysing ancient soft tissue but the extent to which it is used today is limited because of the fragility and value of many ancient samples. For detailed, non-destructive analysis of ancient biological samples, we instead propose x-ray phase-contrast CT, which like conventional CT gives volume data but with the possibility of better resolution through the detection of phase shift. Using laboratory x-ray sources, we here demonstrate the capabilities of phase-contrast tomography of dried biological samples. Virtual histological analysis of a mummified human hand from ancient Egypt is performed, revealing remains of adipose cells in situ, which would not be possible with classical histology. For higher resolution, a lab-based nano-CT arrangement based on a nanofocus transmission x-ray source is presented. With an x-ray emission spot of 300 nm the system shows potential for sub-micronresolution 3D imaging. For characterisation of the performance of phase-contrast imaging of dried samples a piece of wood is imaged. Finally, we present the first phase-contrast CT data from our nano-CT system, acquired of the dried head of a bee.
|
|
