| 1. |
- Dimopoulou, Angeliki, 1975-
(författare)
-
CT with 3D-Image Reconstructions in Preoperative Planning
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computed tomography is one of the most evolving fields of modern radiology. The current CT applications permit among other things angiography, 3D image reconstructions, material decomposition and tissue characterization. CT is an important tool in the assessment of specific patient populations prior to an invasive or surgical procedure. The aim of this dissertation was to demonstrate the decisive role of CT with 3D-image reconstructions in haemodialysis patients scheduled to undergo fistulography, in patients undergoing surgical breast reconstructions with a perforator flap and in patients with complicated renal calculi scheduled to undergo percutaneous nephrolithotomy.CT Angiography with 3D image reconstructions was performed in 31 patients with failing arteriovenous fistulas and grafts, illustrating the vascular anatomy in a comprehensive manner in 93.5% of the evaluated segments and demonstrating a sensitivity of 95% compared to fistulography.In 59 mastectomy patients scheduled to undergo reconstructive breast surgery with a deep inferior epigastric perforator flap, the preoperative planning with CT Angiography with 3D image reconstructions of the anterior abdominal wall providing details of its vascular supply, reduced surgery time significantly (p< 0.001) and resulted in fewer complications.Dual Energy CT Urography with advanced image reconstructions in 31 patients with complicated renal calculi scheduled to undergo PNL, resulted in a new method of material characterisation (depicting renal calculi within excreted contrast) and in the possibility of reducing radiation dose by 28% by omitting the nonenhanced scanning phase. Detailed analysis of the changes renal calculi undergo when virtually reconstructed was performed and a comparison of renal calculi number, volume, height and attenuation between virtual nonenhanced and true nonenhanced images was undertaken. All parameters were significantly underestimated in the virtual nonenhanced images.CT with 3D-reconstructions is more than just “flashy images”. It is crucial in preoperative planning, optimizes various procedures and can reduce radiation dose.
|
|
| 2. |
- Gyllensvärd, Frida, 1980-
(författare)
-
Efficient Methods for Volumetric Illumination
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern imaging modalities can generate three-dimensional datasets with a very high detail level. To transfer all the information to the user in an efficient way there is a need for three-dimensional visualization. In order to enhance the diagnostic capabilities the utilized methods must supply the user with fast renderings that are easy to interpret correctly.It can thus be a challenge to visualize a three-dimensional dataset in a way that allows the user to perceive depth and shapes. A number of stereoscopic solutions are available on the market but it is in many situations more practical and less expensive to use ordinary two-dimensional displays. Incorporation of advanced illumination can, however, improve the perception of depth in a rendering of a volume. Cast shadows provide the user with clues of distances and object hierarchy. Simulating realistic light conditions is, however, complex and it can be difficult to reach interactive frame rates. Approximations and clever implementations are consequently required.This thesis presents efficient methods for calculation of illumination with the objective of providing the user with high spatial and shape perception. Two main types of light conditions, a single point light source and omni-directional illumination, are considered. Global transport of light is efficiently estimated using local piecewise integration which allows a graceful speed up compared to brute force techniques. Ambient light conditions are calculated by integrating the incident light along rays within a local neighborhood around each point in the volume.Furthermore, an approach that allows the user to highlight different tissues, using luminous materials, is also available in this thesis. A multiresolution data structure is employed in all the presented methods in order to support evaluation of illumination for large scale data at interactive frame rates.
|
|
| 3. |
- Jiang, Yiwen, 1982-
(författare)
-
Interplay Between Cell of Origin and Oncogenic Activation in Glioma
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glioma is the most frequent primary tumor of the central nervous system. By using the RCAS/tv-a mouse glioma model, we have studied mechanisms controlling glioma development and the effect of cell of origin on these processes.SOX5 was identified as a brain tumor locus in a retroviral insertional mutagenesis screen of PDGF-B induced mouse gliomas. Here we found that SOX5 could suppress PDGFB-induced glioma development particularly in Ink4a-/- mice. Analysis of putative PDGF-B signaling pathways revealed that the underlying mechanism could involve the activation of AKT and p27, which caused an acute cellular senescence.When cultured in a highly selective serum free medium, glioma-initiating cells could be isolated from mouse GBMs and their self-renewal and proliferation was independent on exogenous EGF and FGF2. Addition of serum into the medium induced aberrant differentiation that was reversible. Specific depletion of viral PDGF-B demonstrated that PDGF-B was necessary for stemness and tumorigenicity of GICs by preventing them to differentiate.Subsequently, by applying the same culture conditions, GICs of APC, NSC and OPC origins were isolated from mouse GBMs. GICs derived from NSCs exhibited higher self-renewal, faster proliferation and more potent tumorigenicity than those of APC or OPC origin. Furthermore, addition of 5% serum significantly inhibited the proliferation of APC- and OPC-derived GICs, but did not in NSC-derived GICs. Transcriptome analysis revealed that GICs of the same cell of origin displayed distinct expression profiles.In the last study, we showed that OPCs could serve as the origin for astrocytic glioma. Results from immunostainings revealed that these tumors might belong to a different molecular subtype than the oligodendroglial tumors induced in OPCs. We also found differences in tumorigenic potential between OPCs in neonatal and adult mice, which suggest that developmental age of the cell of origin is important for its susceptibility to oncogenic transformation.
|
|
| 4. |
- Lundin, Margareta
(författare)
-
Aspects on Image Quality in Radiologic Evaluation of the Urinary Tract
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this document is on image quality as one of the factors fundamental for the diagnostic process. With the rising number of procedures and the trend towards more complicated examinations, urinary tract investigations was chosen in this work as a good clinical model for evaluation of the factors influencing image quality and of the ways of evaluating image quality.In paper I, a method is described for optimisation during the introduction of a new imaging system, with a focus on the maintenance of image quality relative to the older already optimised system. Image quality was assessed using the image criteria of the European guidelines for IVU with visual grading analysis. Equivalent image quality in image pairs was achieved at 30% of the dose. The CDRAD contrast-detail phantom makes it possible to find dose levels that give equal image quality using different imaging systems.In paper II, the influence of bowel purgation on image quality in urography is questioned. The aim of this study was to compare bowel purgation and two other preparation methods; dietary restrictions and no preparation at all. Image quality was assessed according to European Commission criteria for excretory urography. The effectiveness of bowel purgation and the amount of residual gas were scored separately. The results of our study show that the preparation methods are of equal value and further use of bowel purgation before excretory urography cannot be justified.In paper III, the image quality of the non-enhanced series is compared to a virtual noncontrast series obtained using two generations of dual-energy CT scanners and taking CT of the urinary tract as a model. The image quality of the VNC images was rated inferior to the single-energy variant for both scanners, the OR range being 11.5–67.3 for the Definition and 2.1–2.8 for the Definition Flash. Visual noise and overall quality were regarded as better with Flash than with Definition. Image quality of VNC images obtained with the new generation of DECT is still slightly inferior compared to native images.In paper IV, the accuracy of measurement of renal calculi in a dual-energy, virtual, nonenhanced-image series is compared to actual stone size and a single-energy image series in the phantom study. This study shows that detection of small stones is not reliable, despite better image quality, with the new DECT and that small stones will be missed with VNC imaging. With larger stones, the inherent measurement error with CT is magnified with VNC imaging.
|
|
| 5. |
- Persson, Anders
(författare)
-
Defining, Securing and Building a Just Peace : The EU and the Israeli-Palestinian conflict
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Just peace has been much talked about in everyday life, but it is less well researched by academics. The puzzle underlying this dissertation is therefore to probe what constitutes a just peace, both conceptually within the field of peacebuilding and empirically in the context of the EU as a peacebuilder in the Israeli-Palestinian conflict. The EU has used the term just peace in many of its most important declarations on the Israeli-Palestinian conflict throughout the years. Defining a just peace is about these declaratory efforts by the EU to articulate a common formula of a just peace in the conflict. Securing and building a just peace are about the EU’s role in implementing this formula for a just peace in the conflict through the creation of a Palestinian state. As the EU enters its fifth decade of involvement in the conflict, there can be little doubt that in common with the rest of the international community it has failed in its efforts to establish a just peace between Israelis and Palestinians. While this is an inescapable overall conclusion from four decades of EC/EU peacebuilding in the conflict, it is, at the same time, possible to draw a number of other conclusions from this study. Most importantly, it will be argued that the EU is a major legitimizing power in the conflict and that it has kept the prospects of a two-state solution alive through its support for the Palestinian statebuilding process.
|
|
| 6. |
- Persson, Anders, 1982-
(författare)
-
Magnetoresistance and Space : Micro- and Nanofeature Sensors Designed, Manufactured and Evaluated for Space Magnetic Field Investigations
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, the interest for miniaturization of spaceborne instruments and subsystems has increased steadily, as this enables development of small and lightweight satellite classes as well as more versatile payloads on traditional spacecraft. In essence, this thesis work is an investigation of the applicability of magnetoresistive technology to a magnetometer intended for space. Two types of magnetoresistive sensors, promising with respect to performance competiveness also after considerable miniaturization, were developed and evaluated, namely magnetic tunnel junctions and planar Hall effect bridge sensors. In the case of the magnetic tunnel junctions, much effort was put on the micromanufacturing process. Two schemes were developed and evaluated for sensor contouring: one employing focused ion beam processes for rapid prototyping, and the other combining sputtering and x-ray photoelectron spectroscopy for precise etch depth monitoring during ion etching. For the former, the resulting implantation damages were investigated with chemical analysis and correlated to the sensor properties. In the latter, the depth of the etching was monitored live with a resolution sufficient to stop the etching in the 1 nm thick tunneling barrier. The effect and extent of redeposition were investigated by transmission electron microscopy and micromagnetic analysis. With the knowledge so gained, the tunneling magnetoresistance of the manufactured junctions could be improved significantly and their inherent noise could be reduced. As a step in space flight qualification, the magnetic tunnel junctions were subjected to both g and particle radiation, leaving them unaffected by the first, but rendering them a reduced tunneling magnetoresistance ratio and an increased coercivity by the latter. In the case of the planar Hall effect bridge sensors, their inherent noise was thoroughly investigated, revealing both electric and magnetic 1/f noise at low frequencies along with thermal noise at higher frequencies. In addition, an analytical model of the magnetic properties of the planar Hall effect bridges was developed, and a design process, based on the model, was established to optimize the bridges for a particular application. In conclusion, both types of sensors show great promises for use in space. Of the two, the planar Hall effect bridge sensors had a better detection limit at low frequencies, whereas the magnetic tunnel junctions were more precise at higher frequencies. However, both sensors had a bandwidth greatly exceeding that of traditional spaceborne magnetometers. A magnetometer employing the magnetic tunnel junctions from this work is currently included as payload onboard the Vietnamese satellite F-1 scheduled for launch this year. A magnetometer using magnetoresistive sensors – planar Hall effect sensors, magnetic tunnel junctions, or both – enables a mass reduction of more than two orders of magnitudes compared with traditional systems.
|
|
| 7. |
- Wang, Chunliang, 1980-
(författare)
-
Computer-Assisted Coronary CT Angiography Analysis : From Software Development to Clinical Application
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Advances in coronary Computed Tomography Angiography (CTA) have resulted in a boost in the use of this new technique in recent years, creating a challenge for radiologists due to the increasing number of exams and the large amount of data for each patient. The main goal of this study was to develop a computer tool to facilitate coronary CTA analysis by combining knowledge of medicine and image processing, and to evaluate the performance in clinical settings.Firstly, a competing fuzzy connectedness tree algorithm was developed to segment the coronary arteries and extract centerlines for each branch. The new algorithm, which is an extension of the “virtual contrast injection” (VC) method, preserves the low-density soft tissue around the artery, and thus reduces the possibility of introducing false positive stenoses during segmentation. Visually reasonable results were obtained in clinical cases.Secondly, this algorithm was implemented in open source software in which multiple visualization techniques were integrated into an intuitive user interface to facilitate user interaction and provide good overviews of the processing results. An automatic seeding method was introduced into the interactive segmentation workflow to eliminate the requirement of user initialization during post-processing. In 42 clinical cases, all main arteries and more than 85% of visible branches were identified, and testing the centerline extraction in a reference database gave results in good agreement with the gold standard.Thirdly, the diagnostic accuracy of coronary CTA using the segmented 3D data from the VC method was evaluated on 30 clinical coronary CTA datasets and compared with the conventional reading method and a different 3D reading method, region growing (RG), from a commercial software. As a reference method, catheter angiography was used. The percentage of evaluable arteries, accuracy and negative predictive value (NPV) for detecting stenosis were, respectively, 86%, 74% and 93% for the conventional method, 83%, 71% and 92% for VC, and 64%, 56% and 93% for RG. Accuracy was significantly lower for the RG method than for the other two methods (p<0.01), whereas there was no significant difference in accuracy between the VC method and the conventional method (p = 0.22).Furthermore, we developed a fast, level set-based algorithm for vessel segmentation, which is 10-20 times faster than the conventional methods without losing segmentation accuracy. It enables quantitative stenosis analysis at interactive speed.In conclusion, the presented software provides fast and automatic coronary artery segmentation and visualization. The NPV of using only segmented 3D data is as good as using conventional 2D viewing techniques, which suggests a potential of using them as an initial step, with access to 2D reviewing techniques for suspected lesions and cases with heavy calcification. Combining the 3D visualization of segmentation data with the clinical workflow could shorten reading time.
|
|
| 8. |
- Widén, Pär
(författare)
-
Bedömningsmakten : Berättelser om stat, lärare och elev, 1960‐1995
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Avhandlingen handlar om hur bedömningssystemet i bred bemärkelse presenterades i betygsdebatten i samband de politiska besluten om betygssystemet för gymnasiet mellan 1960 och 1995. Avhandlingen tar sin utgångspunkt i de berättelser som konstruerades under perioden. Syftet är att spåra och tolka förändringar i berättelserna om bedömning i anslutning till det politiska projektet att demokratisera och individualisera skolsystemet. Fokus är särskilt riktat mot de bedömningstekniker och innebörder för relationen mellan stat, lärare och elever som aktualiserades i samband med de två gymnasiereformerna. Härigenom synliggörs en viktig definitionskamp om statens förhållande till individen - lärare och elever - och hur makten i den nya enhetliga och demokratiska gymnasieskolan skulle förstås och organiseras. Avhandlingen pekar också på hur berättelser konkurrerar och hur en berättelse kan ges olika innebörder i förhållande till det politiska projektet att skapa en skola som tar till vara elevernas demokratiska möjligheter och lika villkor.
|
|
