| 1. |
- Andersson, Patrik, et al.
(författare)
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Effects of lung tissue characterization in radiotherapy of breast cancer under deep inspiration breath hold when using Monte Carlo dosimetry
- 2021
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Ingår i: Physica medica (Testo stampato). - : Associazione Italiana di Fisica Medica. - 1120-1797 .- 1724-191X. ; 90, s. 83-90
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To investigate the sensitivity of Monte Carlo (MC) calculated lung dose distributions to lung tissue characterization in external beam radiotherapy of breast cancer under Deep Inspiration Breath Hold (DIBH). Methods: EGSnrc based MC software was employed. Mean lung densities for one hundred patients were analysed. CT number frequency and clinical dose distributions were calculated for 15 patients with mean lung density below 0.14 g/cm3. Lung volume with a pre-defined CT numbers was also considered. Lung tissue was characterized by applying different CT calibrations in the low-density region and air-lung tissue thresholds. Dose impact was estimated by Dose Volume Histogram (DVH) parameters. Results: Mean lung densities below 0.14 g/cm3 were found in 10% of the patients. CT numbers below −960 HU dominated the CT frequency distributions with a high rate of CT numbers at −990 HU. Mass density conversion approach influenced the DVH shape. V4Gy and V8Gy varied by 7% and 5% for the selected patients and by 9% and 3.5% for the pre-defined lung volume. V16Gy and V20Gy, were within 2.5%. Regions above 20 Gy were affected. Variations in air- lung tissue differentiation resulted in DVH parameters within 1%. Threshold at −990 HU was confirmed by the CT number frequency distributions. Conclusions: Lung dose distributions were more sensitive to variations in the CT calibration curve below lung (inhale) density than to air-lung tissue differentiation. Low dose regions were mostly affected. The dosimetry effects were found to be potentially important to 10% of the patients treated under DIBH.
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| 2. |
- Andersson, Peter, 1975, et al.
(författare)
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Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams
- 2023
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Ingår i: Biomedical Engineering & Physics Express. - : Institute of Physics. - 2057-1976. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Purpose. To investigate the response of the CC13 ionization chamber under non-reference photon beam conditions, focusing on penumbra and build-up regions of static fields and on dynamic intensity-modulated beams. Methods. Measurements were performed in 6 MV 100 × 100, 20 × 100, and 20 × 20 mm2 static fields. Monte Carlo calculations were performed for the static fields and for 6 and 15 MV dynamic beam sequences using a Varian multi-leaf collimator. The chamber was modelled using EGSnrc egs_chamber software. Conversion factors were calculated by relating the absorbed dose to air in the chamber air cavity to the absorbed dose to water. Correction and point-dose correction factors were calculated to quantify the conversion factor variations. Results. The correction factors for positions on the beam central axis and at the penumbra centre were 0.98-1.02 for all static fields and depths investigated. The largest corrections were obtained for chamber positions beyond penumbra centre in the off-axis direction. Point-dose correction factors were 0.54-0.71 at 100 mm depth and their magnitude increased with decreasing field size and measurement depth. Factors of 0.99-1.03 were obtained inside and near the integrated penumbra of the dynamic field at 100 mm depth, and of 0.92-0.94 beyond the integrated penumbra centre. The variations in the ionization chamber response across the integrated dynamic penumbra qualitatively followed the behaviour across penumbra of static fields. Conclusions. Without corrections, the CC13 chamber was of limited usefulness for profile measurements in 20-mm-wide fields. However, measurements in dynamic small irregular beam openings resembling the conditions of pre-treatment patient quality assurance were feasible. Uncorrected ionization chamber response could be applied for dose verification at 100 mm depth inside and close to large gradients of dynamically accumulating high- and low-dose regions assuming 3% tolerance between measured and calculated doses. © 2023 The Author(s).
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| 3. |
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| 4. |
- Colaço, Marcos, et al.
(författare)
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Characterization of the microstructures of specialty optical fibers for electric-field sensing by propagation-based x-ray phase-contrast microtomography
- 2021
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Ingår i: Measurement science and technology. - : IOP Publishing Ltd. - 0957-0233 .- 1361-6501. ; 32:6
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a quantitative (statistical) 3D morphological characterization of optical fibers used in electric-field sensing. The characterization technique employs propagation-based x-ray phase-contrast microcomputed tomography (micro-CT). In particular, we investigate specialty optical fibers that contain microstructured holes that are electro-optically modified by thermal poling to induce second-order nonlinear effects (SONE). The efficiency of the SONE is reflected in the characterization parameter, Vπ, which is highly dependent on the dimensions of the fiber. The fiber microstructures must be uniform to support the fabrication of reproducible devices. The results obtained using the micro-CT technique show that uncertainty of ±1.7% arises in the determination of the expected value of the voltage that causes a change in the phase of the electromagnetic wave equal to π rad (Vπ ), demonstrating a great advantage, compared with other techniques e.g. SEM, which would need at least 1000 images of the cross-section of an optical fiber, taken at different points, making the process more expensive and time-consuming.
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| 5. |
- Döse, Magnus, et al.
(författare)
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Naturally occurring radioactivity in some Swedish concretes and their constituents - Assessment by using I-index and dose-model
- 2016
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Ingår i: Journal of Environmental Radioactivity. - : Elsevier. - 0265-931X .- 1879-1700. ; 155-156, s. 105-111
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Tidskriftsartikel (refereegranskat)abstract
- The reference level for effective dose due to gamma radiation from building materials and construction products used for dwellings is set to 1 mSv per year (EC, 1996, 1999), (CE, 2014). Given the specific conditions presented by the EC in report 112 (1999) considering building and construction materials, an I-index of 1 may generate an effective dose of 1 mSv per year. This paper presents a comparison of the activity concentrations of 4 0K, 226Ra and 232Th of aggregates and when these aggregates constitute a part of concrete. The activity concentration assessment tool for building and construction materials, the I-index, introduced by the EC in 1996, is used in the comparison. A comparison of the I-indices values are also made with a recently presented dose model by Hoffman (2014), where density variations of the construction material and thickness of the construction walls within the building are considered. There was a ~16-19% lower activity index in concretes than in the corresponding aggregates. The model by Hoffman further implies that the differences between the I-indices of aggregates and the concretes' final effective doses are even larger. The difference is due, mainly to a dilution effect of the added cement with low levels of natural radioisotopes, but also to a different and slightly higher subtracted background value (terrestrial value) used in the modeled calculation of the revised I-index by Hoffman (2014). Only very minimal contributions to the annual dose could be related to the water and additives used, due to their very low content of radionuclides reported.
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| 6. |
- Ekberg, Olle, et al.
(författare)
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Effect of barium sulfate contrast medium on rheology and sensory texture attributes in a model food
- 2009
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Ingår i: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 50:2, s. 131-138
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Tidskriftsartikel (refereegranskat)abstract
- Background: The swallowing process can be visualized using videoradiography, by mixing food with contrast medium, e.g., barium sulfate (BaSO4), making it radiopaque. The sensory properties of foods may be affected by adding this medium. Purpose: To evaluate if and to what extent sensory and rheological characteristics of mango puree were altered by adding barium sulfate to the food. Material and Methods: This study evaluated four food samples based on mango puree, with no or added barium sulfate contrast medium (0%, 12.5%, 25.0%, and 37.5%), by a radiographic method, and measured sensory texture properties and rheological characteristics. The sensory evaluation was performed by an external trained panel using quantitative descriptive analysis. The ease of swallowing the foods was also evaluated. Results: The sensory texture properties of mango puree were significantly affected by the added barium in all evaluated attributes, as was the perception of particles. Moreover, ease of swallowing was significantly higher in the sample without added contrast medium. All samples decreased in extensional viscosity with increasing extension rate, i.e., all samples were tension thinning. Shear viscosity was not as dependent on the concentration of BaSO4 as extensional viscosity. Conclusion: Addition of barium sulfate to a model food of mango puree has a major impact on perceived sensory texture attributes as well as on rheological parameters. © 2009 Informa UK Ltd.
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| 7. |
- Ekberg, Olle, et al.
(författare)
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Flow properties of oral contrast medium formulations depend on the temperature
- 2010
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Ingår i: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 51:4, s. 363-367
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Tidskriftsartikel (refereegranskat)abstract
- Background: During the therapeutic videofluoroscopic examination of swallowing, gradation of bolus volume, texture, and viscosity can be implemented to determine the optimal bolus characteristics in that particular patient. When a thickened liquid is given to a dysphagic patient it is served at room temperature. However, in these patients with a delayed oral and/or pharyngeal stage of swallow, the bolus is held for a long time in the oral cavity. The temperature of the thickened liquid thereby increases. Purpose: To study the rheological exploration (variation of viscosity with temperature) of thickened food used for radiologic swallowing examinations in patients with oral and pharyngeal dysfunction, in particular in mixtures of barium sulfate suspensions and in iodine solutions. Material and Methods: Deep-frozen mango purée was thawed at room temperature. It was then mixed with barium sulfate contrast medium to a density of 25% w/w. Resorce® Thicken Up was mixed at room temperature at two concentrations: 4.3% w/w (4.5 g thickener + 100 g distilled water) and 6.0% w/w (4.5 g thickener + 70 g distilled water). The thickener consisted of modified corn starch. Resorce® Thicken Up was also mixed at room temperature with two concentrations of an iodine contrast material, iohexol (Omnipaque®, 350 mg I/ml). The two concentrations were: 4.3% w/w (4.5 g thickener + 100 g iohexol) and 6% w/w (6 g thickener + 100 g iohexol). Measurements were carried out from 20°C to 37°C using a Stresstech HR rheometer. The rheometer was equipped with a concentric cylinder measuring system (inner cylinder 15 mm). Results: The samples containing thickener in water as well as in iohexol showed a dependence on thickener concentration and temperature. The mango purée with barium sulfate displayed very small temperature dependence. The thickener solutions in iohexol had significantly higher viscosity compared with the other thickener solutions and the mango purée. The relative decrease shows that mango purée, the 6% thickener solution in water, and solutions with iohexol exhibited similar relative viscosity change at different temperatures. Conclusion: Our conclusion is therefore that it is important always to make the solution with high precision. It is also of importance to observe how long the patient keeps the bolus in the mouth. This might vary and actually it may not be possible to influence this factor. When different types of thickeners are compared, it is important to take into account the temperature at which the thickener is observed.
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| 8. |
- Etcheverry, Sebastian, et al.
(författare)
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Identification and collection of particles with optical fibers
- 2015
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Ingår i: NOVEL BIOPHOTONICS TECHNIQUES AND APPLICATIONS III. - : SPIE. - 9781628417050
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Konferensbidrag (refereegranskat)abstract
- A micro-structured fiber-based system for identification and collection of fluorescent particles is demonstrated. An optical fiber probe with longitudinal holes in the cladding is used to retrieve fluorescent particles by exerting microfluidics forces. Laser induced fluorescent (LIF) is carried out by the fiber probe and an optical setup. When a particle with a previously chosen fluorescence wavelength is identified, a vacuum pump is activated collecting the particle into a hole. Green and red fluorescent polystyrene particles were detected and selectively retrieved.
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| 9. |
- Miettinen, Arttu, et al.
(författare)
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A non-destructive X-ray microtomography approach for measuring fibre length in short-fibre composites
- 2012
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 72:15, s. 1901-1908
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Tidskriftsartikel (refereegranskat)abstract
- An improved method based on X-ray microtomography is developed for estimating fibre length distribution of short-fibre composite materials. In particular, a new method is proposed for correcting the biasing effects caused by the finite sample size as defined by the limited field of view of the tomographic devices. The method is first tested for computer generated fibre data and then applied in analyzing the fibre length distribution in three different types of wood fibre reinforced composite materials. The results were compared with those obtained by an independent method based on manual registration of fibres in images from a light microscope. The method can be applied in quality control and in verifying the effects of processing parameters on the fibre length and on the relevant mechanical properties of short fibre composite materials, e.g. stiffness, strength and fracture toughness.
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| 10. |
- Rothenberg, E., et al.
(författare)
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Texture-modified meat and carrot products for elderly people with dysphagia : Preference in relation to health and oral status
- 2007
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Ingår i: Scandinavian Journal of Food and Nutrition. - : Informa UK Limited. - 1748-2976 .- 1748-2984. ; 51:4, s. 141-147
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Tidskriftsartikel (refereegranskat)abstract
- Background: Reduced taste and smell, chewing problems and swallowing dysfunction are common among elderly people and affect perception, food choice and the ability to eat. Objective: To study the preference for texture-modified carrot and meat products in elderly people aiming to meet the needs of people with impaired chewing and/or swallowing. Design: Data were collected using questionnaires focusing on health, oral status and preference for the products. Altogether, 108 elderly people in ordinary housing (OH) and 50 living in special housing (SH) in Malmö (SH-M) and Göteborg (SH-G) participated. Results: 19% had a body mass index ?22, predominantly in SH (24%). Stroke was reported by 20% of the subjects in SH. Among those with subjectively experienced difficulties in swallowing (12%), 58% reported coughing, 21% a gurgly voice in association with food intake and 50% obstruction during swallowing. Only 20% with subjective swallowing difficulties had been specifically examined regarding this problem. All the tested products were easy to masticate and swallow. Compared with OH, people in SH-M found the meat products easier to masticate and swallow. Compared with OH, subjects in SH found the carrot products easier to masticate Conclusions: There is a need to develop tasty texture-modified nutritious food products for people with mastication and/or swallowing problems. Possible factors for differences in preference between groups, in this study OH and SH, may be related to health status in general and specifically mastication and swallowing functions. © 2007 Taylor & Francis.
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