Pulmonary diseases are characterized by small-scale and large-scale alterations in structure and function of the lung. Multidetector-row computed tomography (MDCT) is a powerful tool for quantitatively assessing small-scale lung structure including parenchymal destruction, air trapping and airway remodeling. When combined with novel imaging techniques and contrast agents, measuring small-scale regional ventilation (rV̇A) and perfusion (rQ̇) also becomes possible. This thesis focuses on developing and evaluating MDCT-based tools for measuring regional lung function in animal models and transitioning them to studying humans. Wash-in xenon-CT rV̇A measurements acquired in an animal model were validated with inhaled fluorescent microspheres (FMS), an invasive but recognized gold standard. Xenon-CT correlated well with FMS, demonstrating similar gradients in prone and supine postures. Small-scale rV̇A measurements from xenon-CT were less susceptible to partial voluming and resulted in reduced scatter. To facilitate the measurement of regional structure and function on awake-free-breathing humans, we developed systems for lung volume standardization during scanning for both static and dynamic breathing. Anesthetic properties dictated using 30% rather than 55% xenon-gas, reducing signal-to-noise ratio. This reduction, in addition to the influence of free breathing, made xenon-CT more susceptible to noise and required additional post-processing to bolster confidence in rV̇A measurements acquired in humans. Improvements to the available curve-fit algorithms were made and 4D image registration was developed to align time-series datasets. Applying these techniques, we compared rV̇A between normal never-smokers (NS), normal smokers (SNI), normal smokers with early signs of centrilobular emphysema not evident by PFTs (SCE) and smokers with COPD. There was increased heterogeneity in SNI versus NS and time constants were lengthened in COPD and in SCE. This is consistent with our earlier hypothesis that while patchy inflammation will occur in all smokers, only a subset of the population with decreased rQ̇ in regions of inflammation stemming from a failure to block HPV will be susceptible to emphysema. In order to facilitate translation into the clinical research environment, we established dual-energy-CT (DECT) methods to replace more elaborate time-series laboratory-centered techniques. Xe-DECT rV̇A measures were optimized through a series of phantom and animal studies to determine the proper three-material decomposition parameters, imaging parameters, gas mixture and delivery protocol. DECT perfused blood volume was validated as a surrogate for rQ̇ in animal studies in which blood flow patterns were altered by increasing lung inflation or occluding a portion of the pulmonary vasculature. To examine the intricacy of lung function, the effects of disease, and give us insight into their etiology we must study gas-exchange on a small-scale. MDCT-based techniques provide the spatial resolution necessary to examine rV̇A and rQ̇ on a small-scale offering an avenue to identify novel phenotypes that may not only yield insights into disease processes but also may provide tools leading to drug and device developments, outcomes assessment and ultimately to the selection of subpopulations suitable for a particular intervention.

The introduction of dual energy CT, DECT, in the field of medical healthcare has made it possible to extract more information of the scanned objects. This in turn has the potential to improve the accuracy in radiation therapy dose planning. One problem that remains before successful material decomposition can be achieved however, is the presence of beam hardening and scatter artifacts that arise in a scan. Methods currently in clinical use for removal of beam hardening often bias the CT numbers. Hence, the possibility for an appropriate tissue decomposition is limited. Here a method for successful decomposition as well as removal of the beam hardening artifact is presented. The method uses effective linear attenuations for the five base materials, water, protein, adipose, cortical bone and marrow, to perform the decomposition on reconstructed simulated data. This is performed inside an iterative loop together with the polychromatic x-ray spectra to remove the beam hardening

El objetivo que ha motivado esta tesis ha sido el analizar y proponer mecanismos para incrementar la capacidad de tráfico de un sistema de acceso radio DECT (Digital Enhanced Cordless Telecommunications) en entornos de exteriores, particularmente en los servicios de bucle de abonado vía radio y CTM (Cordless Terminal Mobility).El DECT fue diseñado en un principio para trabajar en entornos de interiores con alta capacidad de tráfico y calidad de voz comparable a un teléfono con hilos. Sin embargo, cuando el sistema debe operar en exteriores las condiciones de propagación cambian radicalmente y no se consiguen los mismos rendimientos que en interiores.Dentro de edificios se aprovechan las atenuaciones de paredes, techos y otros objetos para tener un gran reuso de los canales, el principal problema que presentan los escenarios de exteriores es que las señales interferentes se propagan con mucha más facilidad y la interferencia generada por el propio sistema limita su capacidad.En la tesis se presentan cuatro tipos de resultados analizados mediante un simulador software. El primer grupo está enfocado a incrementar la capacidad del sistema de bucle de abonado vía radio utilizando antenas directivas, control de potencia, arrays adaptativos y la posibilidad de que las estaciones base transmitan información de cuales son sus canales menos interferidos.El segundo tipo de resultados evalúa las prestaciones de la aplicación de CTM con usuarios móviles y diferentes posiciones de las estaciones base. El tercer tipo analiza técnicas que maximizan la eficiencia de los recursos más que la capacidad de tráfico, se han utilizado repetidores y antenas distribuidas. El último grupo de resultados examina al sistema de bucle de abonado en condiciones adversas de tráfico no uniforme y con dos operadores trabajando en la misma zona sin estar sincronizados.

Brachytherapy is radiation therapy performed by placing a radiation source near or inside a tumor. Difference between the current water-based brachytherapy dose formalism (TG-43) and new model based dose calculation algorithms (MBSCAs) can differ by more than a factor of 10 in the calculated doses. There is a need for voxel-by-voxel cross-section assignment, ideally, both the tissue composition and mass density of every voxel should be known for individual patients. A method for determining tissue composition via three material decomposition (3MD) from dual energy CT scans was developed at Linköping university. The method (named DIRA) is a model based iterative reconstruction algorithm that utilizes two photon energies for image reconstruction and 3MD for quantitative tissue classification of the reconstructed volumetric dataset. This thesis has investigated the accuracy of the 3MD method applied on prostate tissue in an anthropomorphic phantom when using two different approximations of soft tissues in DIRA. Also the distributions of CT-numbers for soft tissues in a contemporary dual energy CT scanner have been determined. An investigation whether these distributions can be used for tissue classification of soft tissues via thresholding has been conducted. It was found that the relative errors of mass energy absorption coefficient (MEAC) and linear attenuation coefficient (LAC) of the approximated mixture as functions of photon energy were less than 6 \% in the energy region from 1 keV to 1 MeV. This showed that DIRA performed well for the selected anthropomorphic phantom and that it was relatively insensitive to choice of base materials for the approximation of soft tissues. The distributions of CT-numbers of liver, muscle and kidney tissues overlapped. For example a voxel containing muscle could be misclassified as liver in 42 cases of 100. This suggests that pure thresholding is insufficient as a method for tissue classification of soft tissues and that more advanced methods should be used.

There is a need for quantitative CT data in radiation therapy. Currently there are only few algorithms that address this issue, for instance the commercial DirectDensity algorithm. In scientific literature, an example of such an algorithm is DIRA. DIRA is an iterative model-based reconstruction method for dual-energy CT whose goal is to determine the material composition of the patient from accurate linear attenuation coefficients. It has been implemented in a two dimensional geometry, i.e., it could process axial scans only.  There was a need to extend DIRA so that it could process projection data generated in helical scanning geometries. The newly developed algorithm (DIRA-3D) implemented (i) polyenergetic semi-parallel projection generation, (ii) mono-energetic parallel projection generation and (iii) the PI-method for image reconstruction. The computation experiments showed that the accuracies of the resulting LAC and mass fractions were comparable to the ones of the original DIRA. The results converged after 10 iterations.

No description available.

Excessive imaging doses from repeated scans and poor image quality mainly due to scatter contamination are the two bottlenecks of cone-beam CT (CBCT) imaging. This study investigates a method that combines measurement-based scatter correction and a compressed sensing (CS)-based iterative reconstruction algorithm to generate scatter-free images from low-dose data. Scatter distribution is estimated by interpolating/extrapolating measured scatter samples inside blocked areas. CS-based iterative reconstruction is finally carried out on the under-sampled data to obtain scatter-free and low-dose CBCT images. In the tabletop phantom studies, with only 25% dose of a conventional CBCT scan, our method reduces the overall CT number error from over 220 HU to less than 25 HU, and increases the image contrast by a factor of 2.1 in the selected ROIs. Dual-energy CT (DECT) is another important application of CBCT. DECT shows promise in differentiating materials that are indistinguishable in single-energy CT and facilitates accurate diagnosis. A general problem of DECT is that decomposition is sensitive to noise in the two sets of projection data, resulting in severely degraded qualities of decomposed images. The first study of DECT is focused on the linear decomposition method. In this study, a combined method of iterative reconstruction and decomposition is proposed. The noise on the two initial CT images from separate scans becomes well correlated, which avoids noise accumulation during the decomposition process. To fully explore the benefits of DECT on beam-hardening correction and to reduce the computation cost, the second study is focused on an iterative decomposition method with a non-linear decomposition model for noise suppression in DECT. Phantom results show that our methods achieve superior performance on DECT imaging, with respect to noise reduction and spatial resolution.

Dans la pratique actuelle de la curiethérapie à bas débit, l'évaluation de la dose dans la prostate est régie par le protocole défini dans le groupe de travail 43 (TG-43) de l'American Association of Physicists in Medicine. Ce groupe de travail suppose un patient homogène à base d'eau de même densité et néglige les changements dans l'atténuation des photons par les sources de curiethérapie. En considérant ces simplifications, les calculs de dose se font facilement à l'aide d'une équation, indiquée dans le protocole. Bien que ce groupe de travail ait contribué à l'uniformisation des traitements en curiethérapie entre les hôpitaux, il ne décrit pas adéquatement la distribution réelle de la dose dans le patient. La publication actuelle du TG-186 donne des recommandations pour étudier des distributions de dose plus réalistes. Le but de ce mémoire est d'appliquer ces recommandations à partir du TG-186 pour obtenir une description plus réaliste de la dose dans la prostate. Pour ce faire, deux ensembles d'images du patient sont acquis simultanément avec un tomodensitomètre à double énergie (DECT). Les artéfacts métalliques présents dans ces images, causés par les sources d’iode, sont corrigés à l'aide d’un algorithme de réduction d'artefacts métalliques pour DECT qui a été développé dans ce travail. Ensuite, une étude Monte Carlo peut être effectuée correctement lorsque l'image est segmentée selon les différents tissus humains. Cette segmentation est effectuée en évaluant le numéro atomique effectif et la densité électronique de chaque voxel, par étalonnage stoechiométrique propre au DECT, et en y associant le tissu ayant des paramètres physiques similaires. Les résultats montrent des différences dans la distribution de la dose lorsqu'on compare la dose du protocole TG-43 avec celle retrouvée avec les recommandations du TG-186. / In current low dose rate brachytherapy practice, dose evaluation within the prostate is govern by the protocol defined by the task group 43 (TG-43) of the American Association of Physicist in Medicine. This task group assumes a homogeneous water based patient with invariable density. They also disregard the changes in photon attenuation through neighbouring brachytherapy sources. With the introduction of these simplifications, dose calculations are easily solved using an equation proposed in this protocol. Although this task group helped create a uniform practice of brachytherapy treatments between hospitals, it does not properly described the actual dose distribution within the patient. The current publication of TG-186 gives recommendations to study these dose distribution more realistically. The purpose of this Master's thesis is to apply these recommendations from TG-186 to obtain a more realistic description of the dose. In order to proceed, two sets of patient images are acquired with a dual energy computed tomography (DECT). These images are corrected for metallic artifacts, which are highly present in the scanned images, using DECT metallic artifact reduction algortithm, developped in this work. Afterwords, a Monte Carlo study can be performed by properly identifying the environment with human tissues. This segmentation is performed by evaluating the effective atomic number and electronic density of each voxel using a DECT stoichiometric calibration, and allocating the tissue having the closest resemblance to these physical parameters. The results show clear differences in dose distribution when comparing TG-43 protocole with TG-186 recommendations.

<p>This thesis treats the development of wirelessinfrastructure standards resulting from co-operative research,development and standardisation efforts. It strives to identifykey influences on this development process, and toconceptualise the process itself. With this as a basis, it goeson to analyse potential implications for companies in thewireless industry, and for the role of co-operatively developedstandards in this field. The focus of the thesis is on thecreation of standards through development efforts, rather thanthe selection of standards in official forums, or by themarket.</p><p>Two deep empirical studies provide the foundation of thethesis. The first one deals with the development of the DigitalEnhanced Cordless Telecommunications (DECT) standard. DECT isan open, de jure standard that was designed by a number oftelecommunications manufacturers. The standard was formallyapproved by the European Telecommunications Standards Institute(ETSI) in 1992. The second study treats the development ofThird Generation (3G) mobile infrastructure standards, withspecial focus on the radio interface standards such as WidebandCode Division Multiple Access (WCDMA). The development of thefamily of 3G standards today known as International MobileTelecommunications 2000 (IMT-2000) began more than 15 yearsago, and the first version of formally adopted air interfacestandards was released in 2000 by the Third GenerationPartnership Project (3GPP). The research and development goinginto the specification of the standards has involved all majorplayers in the wireless industry.</p><p>The two studies have involved numerous interviews withindustry professionals, academics, regulators, and others. Inaddition, a multitude of technical reports and articles,meeting documents, press releases, etc., have been analysed toprovide good documentation of the development processes. Theempirical studies have also been complemented with extensiveliterature studies into the areas of technical development andstandardisation.</p><p>Apart from two "thick descriptions" of importantdevelopments in the wireless industry, the main result of thethesis is a conceptual framework for how wirelessinfrastructure standards are developed. The frameworkdemonstrates that the development is influenced by thepre-history of the standard in terms of existing systems, aswell as research and development that had been pursued inrelevant fields. Furthermore it shows that preconceptions ofmarket needs and user behaviour are key aspects of the designof the standard. During the development process technologicalcontroversies tend to appear as a manifestation of differentcompetitive intentions among the involved players. In theresolution of these controversies, the stage is set for futurecompetition between suppliers of products adhering to thestandard.</p><p>The pre-history of a standard, as well as the marketpreconceptions, originate in the semi-independent processes oftechnological development, and market diffusion, respectively.When the time frame of the conceptual framework is expanded,generations of standards following upon each other can beidentified. Each new generation incorporates new developments,and improved functionality and performance, but also builds onexisting solutions. The technical standards, such as DECT orWCDMA, act as wasp-like waists between the technologicaldevelopment and the market diffusion processes.</p><p>The thesis shows that wireless infrastructure standards to agreat extent are created through technical development efforts.The processes also involve political, competitive, andregulatory deliberations, but technical content often definesthe form even for these debates. This points to the importanceof considering standards-setting in terms of a developmentprocess rather than as a set of formal decisions made by astandards body. A consequence of this is that companiesdesiring to influence the design of a particular standardshould strive to be in the forefront of research anddevelopment related to that standardisation effort. This is thekey to leading the development of new wireless infrastructurestandards.</p><p><b>Key words:</b>standards, de jure standards,standardisation, standards-development, competition,technological development, wireless communications, wirelessinfrastructures, telecommunications, WCDMA, DECT, IMT-2000,FPLMTS, 3G</p>

One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.