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| 2. |
- Jonsson, Joakim, 1984-
(författare)
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Integration of MRI into the radiotherapy workflow
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The modern day radiotherapy treatments are almost exclusively based on computed tomography (CT) images. The CT images are acquired using x-rays, and therefore reflect the radiation interaction properties of the material. This information is used to perform accurate dose calculation by the treatment planning system, and the data is also well suited for creating digitally reconstructed radiographs for comparing patient set up at the treatment machine where x-ray images are routinely acquired for this purpose.The magnetic resonance (MR) scanner has many attractive features for radiotherapy purposes. The soft tissue contrast as compared to CT is far superior, and it is possible to vary the sequences in order to visualize different anatomical and physiological properties of an organ. Both of these properties may contribute to an increase in accuracy of radiotherapy treatment.Using the MR images by themselves for treatment planning is, however, problematic. MR data reflects the magnetic properties of protons, and thus have no connection to the radiointeraction properties of the material. MRI also has inherent difficulty in imaging bone, which will appear in images as areas of no signal similar to air. This makes both dose calculation and patient positioning at the treatment machine troublesome.There are several clinics that use MR images together with CT images to perform treatment planning. The images are registered to a common coordinate system, a process often described as image fusion. In these cases, the MR images are primarily used for target definition and the CT images are used for dose calculations. This method is now not ideal, however, since the image fusion may introduce systematic uncertainties into the treatment due to the fact that the tumor is often able to move relatively freely with respect to the patients’ bony anatomy and outer contour, especially when the image registration algorithms take the entire patient anatomy in the volume of interest into account.The work presented in the thesis “Integration of MRI into the radiotherapy workflow” aim towards investigating the possibilities of workflows based entirely on MRI without using image registration, as well as workflows using image registration methods that are better suited for targets that can move with respect to surrounding bony anatomy, such as the prostate.
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| 3. |
- Boström, Magnus, 1972-, et al.
(författare)
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IKEA and the Responsible Governance of Supply Chains : IKEA’s work on chemicals in textiles
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report focuses on IKEA’s management and communication surrounding sustainability in general and chemical risks specifically. IKEA’s work is analysed in relation to theoretical concepts around responsibility, supply chain, and governance . The report focuses on IKEA’s visions and organizational structures, its policy instruments to deal with chemical risks, supplier-relations and communication and learning. The study is based on previous scholarly literature, analyses of relevant documents, a field visit at a few of IKEA’s suppliers in southern India, as well as interviews with staff working at IKEA in Sweden. The report focuses on IKEA’s systems and processes for dealing with chemical risks, and not on the implementation of such measures in quantitative terms.
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- Häggström, Ida, 1982-
(författare)
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Quantitative methods for tumor imaging with dynamic PET
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is always a need and drive to improve modern cancer care. Dynamic positron emission tomography (PET) offers the advantage of in vivo functional imaging, combined with the ability to follow the physiological processes over time. In addition, by applying tracer kinetic modeling to the dynamic PET data, thus estimating pharmacokinetic parameters associated to e.g. glucose metabolism, cell proliferation etc., more information about the tissue's underlying biology and physiology can be determined. This supplementary information can potentially be a considerable aid when it comes to the segmentation, diagnosis, staging, treatment planning, early treatment response monitoring and follow-up of cancerous tumors.We have found it feasible to use kinetic parameters for semi-automatic tumor segmentation, and found parametric images to have higher contrast compared to static PET uptake images. There are however many possible sources of errors and uncertainties in kinetic parameters obtained through compartment modeling of dynamic PET data. The variation in the number of detected photons caused by the random nature of radioactive decay, is of course always a major source. Other sources may include: the choice of an appropriate model that is suitable for the radiotracer in question, camera detectors and electronics, image acquisition protocol, image reconstruction algorithm with corrections (attenuation, random and scattered coincidences, detector uniformity, decay) and so on. We have found the early frame sampling scheme in dynamic PET to affect the bias and uncertainty in calculated kinetic parameters, and that scatter corrections are necessary for most but not all parameter estimates. Furthermore, analytical image reconstruction algorithms seem more suited for compartment modeling applications compared to iterative algorithms.This thesis and included papers show potential applications and tools for quantitative pharmacokinetic parameters in oncology, and help understand errors and uncertainties associated with them. The aim is to contribute to the long-term goal of enabling the use of dynamic PET and pharmacokinetic parameters for improvements of today's cancer care.
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- Karlsson, Magnus
(författare)
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Evolution in changing environments revealed by fire melanism in pygmy grasshopper
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- According to theory, genetic diversity can be maintained by environmental variation and the degree of genetic and phenotypic polymorphism may enhance the ability of populations to endure stress imposed by changing environments. In my thesis I used colour polymorphic pygmy grasshoppers (Tetrix subulata) as a model system to explore how environmental variation influenced genetic diversity. I compared population colour morph frequencies between populations in burnt and non-burnt areas and performed experiments to investigate to what extent colour patterns in these insects are determined by genes and influenced by phenotypic plasticity in response to environmental effects experienced during development. My results showed that the frequency of black individuals on average was much higher in recently fire ravaged areas, a condition known as fire melanism. The highest proportion of black individuals was reached within the first year after a fire. After the initial increase, the proportion of black individuals declined again and the distribution among alternative colour morphs became more even. Data for individuals raised in captivity revealed a high correspondence between maternal and offspring colour patterns, indicating a strong genetic influence on colour. Additional experiments demonstrated that the development of colour patterns in pygmy grasshoppers was not influenced by burnt material or high population densities, two environmental cues associated with post fire environments.To test if reduced competition among alternative colour morphs may contribute to the maintenance of colour pattern polymorphism in these insects I examined if average survival was higher in diverse compared to homogeneous groups of individuals. I found that survival increased with colour pattern diversity, presumably due to reduced competition among alternative colour morphs. Relaxation of competition may explain why the distribution among alternative colour patterns changed and became more even after the initial evolution of fire melanism. My results demonstrate that environmental change may cause extremely rapid and reversible evolution, indicate that fluctuating selection may preserve genetic variation and support the notion that polymorphism may increase average individual success and enable populations to withstand environmental change.
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- Knutsson, Axel
(författare)
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Thermal stability and mechanical properties of TiAlN-based multilayer and monolithic coatings
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores the thermal stability, microstructure, mechanical properties and cutting performance of multilayer and monolithic cubic TiAlN hard coatings. The aim is to increase the understanding of how the coatings’ microstructure and properties are affected by a layered structure when exposed to high temperatures.The coatings were deposited on cemented carbide substrates, using a full scale industrial reactive cathodic arc evaporation system at Seco Tools AB. The thermal stability was investigated by differential scanning calorimetry and the microstructure was characterized with analytical transmission electron microscopy, x-ray diffractometry and atom probe tomography. The mechanical properties and cutting performance were studied by nanoindentation and metal machining, respectively.The decomposition of cubic TiAlN transpire in two steps, first by an isostructural decomposition to cubic AlN- and cubic TiN-rich domains, which is followed by a phase transformation of cubic AlN to hexagonal AlN. In this work I show that the isostructural decomposition occurs in two stages, namely: Spinodal decomposition (initial stage) and coarsening (latter stage). During the initial stage, the phase separation proceeds with a constant size of the AlN- and TiN-rich domains, with a measured wavelength of ~2.8 nm. The time needed for the initial stage depends on the temperature as well as the composition. Following the spinodal decomposition, the AlN- and TiN-rich domains coarsen. The coarsening process is kinetically limited by diffusion and is not dependent on the composition.If the cubic TiAlN is grown as a multilayer coating, with TiN as the alternating layer type, the decomposition behavior will be different. The isostructural spinodal decomposition in the multilayers starts at a lower temperature compared to the monolithic TiAlN, while the subsequent transformation from cubic AlN to hexagonal AlN is delayed to higher temperatures. The TiN-layers confine the coarsening of the hexagonal AlN resulting in smaller domains. Mechanical testing reveals that, despite the 60 vol. % of the softer TiN, the asdeposited multilayers show a similar or slightly higher hardness than the monolithic Ti0.34Al0.66N. In addition, the multilayers show a more pronounced age hardening compared to the monoliths.For short annealing times (<1 min) at 850 °C a layer rich in AlN followed by areas rich in TiN is observed parallel to the TiAlN/TiN interfaces in the multilayer stack. This microstructural feature indicates the presence of surface directed spinodal decomposition in the multilayer coatings. The lack of a layered structure further into the TiAlN-layer is due to the growth induced elemental fluctuations, which trigger an earlier onset of the coarsening. The coherency stresses generated across the multilayer interfaces also influence the decomposition. However, in this case the surface directed spinodal decomposition is the dominating mechanism for the altered thermal stability.Finally, during metal machining of AISI-316L stainless steel the Ti0.34Al0.66N/TiN multilayers, regardless of period, show an improved crater wear resistance compared to a Ti0.34Al0.66N monolith. The multilayer structure and the local coherency across the multilayer interfaces, seen in the as-deposited state, is present also after the metal machining. It is further revealed that the Ti0.34Al0.66N layer decomposes to AlN- and TiN-rich domains during the cutting operation.
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| 8. |
- Mahmood, Faraz, et al.
(författare)
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Decoupling techniques of compact and broadband MIMO antennas for handheld devices
- 2012
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Ingår i: IEEE 6th European Conference on Antennas and propagation (EuCAP 2012). ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- This paper presents an innovative MIMO antenna system consisting of two broadband antennas combined with a 90° or 180° hybrid coupler. The antenna system is suitable for future MIMO systems due to its wide decoupled bandwidth (from 698 to 2700 MHz) covering 23 frequency bands of LTE. Enhanced antenna performance is achieved by radiator slitting and ground plane modification. Moreover, supplemental meandered line ground structures are utilized to miniaturize the antenna size. The low profile antenna with its wide impedance bandwidth, high efficiency, low correlation and quasi-omni directional radiation pattern is attractive for the existing and future 4G mobile communication devices. Simulated and measured results including input reflection, mutual coupling, correlation, and antenna efficiency is presented and analyzed.
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| 9. |
- Olsson, Per-Magnus, 1976-
(författare)
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Positioning Algorithms for Surveillance Using Unmanned Aerial Vehicles
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surveillance is an important application for unmanned aerial vehicles (UAVs). The sensed information often has high priority and it must be made available to human operators as quickly as possible. Due to obstacles and limited communication range, it is not always possible to transmit the information directly to the base station. In this case, other UAVs can form a relay chain between the surveillance UAV and the base station. Determining suitable positions for such UAVs is a complex optimization problem in and of itself, and is made even more difficult by communication and surveillance constraints.To solve different variations of finding positions for UAVs for surveillance of one target, two new algorithms have been developed. One of the algorithms is developed especially for finding a set of relay chains offering different trade-offs between the number of UAVsand the quality of the chain. The other algorithm is tailored towards finding the highest quality chain possible, given a limited number of available UAVs.Finding the optimal positions for surveillance of several targets is more difficult. A study has been performed, in order to determine how the problems of interest can besolved. It turns out that very few of the existing algorithms can be used due to the characteristics of our specific problem. For this reason, an algorithm for quickly calculating positions for surveillance of multiple targets has been developed. This enables calculation of an initial chain that is immediately made available to the user, and the chain is then incrementally optimized according to the user’s desire.
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