Inversion Recovery (IR) is a powerful tool for contrast manipulation in Mag- netic Resonance Imaging (MRI). IR can provide strong contrast between tissues with different values of T1 relaxation times. The tissue magnetization stored at an IR image pixel can take positive as well as negative values. The corresponding polarity information is contained in the phase of the complex image. Due to numerous factors associated with the Magnetic Resonance (MR) scanner and the associated acquisition system, the acquired complex image is modulated by a spatially varying background phase which makes the retrieval of polarity information non-trivial. Many commercial MR scanners perform magnitude-only reconstruction which, due to loss of polarity information, reduces the dynamic contrast range. Phase sensitive IR (PSIR) can provide enhanced image contrast by estimating and removing the background phase and retrieving the correct polarity information. In this thesis, the background phase of complex MR image is modeled using a statistical model based on Markov Ran- dom Fields (MRF). Two model optimization methods have been developed. The first method is a computationally effcient algorithm for finding semi-optimal solutions satisfying the proposed model. Using an adaptive model neighborhood, it can recon- struct low SNR images with slow phase variations. The second method presents a region growing approach which can handle images with rapid phase variations. Ex- perimental results using computer simulations and in vivo experiments show that the proposed method is robust and can perform successful reconstruction even in adverse cases of low signal to noise ratios (SNRs) and high phase variations.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20257号 / 医博第4216号 / 新制||医||1020(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 宮本 享, 教授 村井 俊哉, 教授 高橋 淳 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

Osteoarthritis is the most common type of arthritis, and is characterized by the loss of articular cartilage in a joint. This eventually leads to painful bone on bone interactions. Since the loss of cartilage is permanent, the main treatment for this disease is pain management until a full joint replacement is needed. To test new potential treatments a consistent way to measure cartilage thickness is needed. The current standard used in the knee to represent cartilage uses joint space width measured from x-rays. This measurement is highly variable, and does not directly show cartilage. Unlike x-rays, magnetic resonance imaging (MRI) can provide direct visualization of soft tissues in the body, like cartilage. One specific MRI method called balanced steady-state free precession (bSSFP) provides useful contrast between cartilage and its surrounding tissues. This allows easy delineation of the cartilage for volume and thickness measurements. Using bSSFP has unique challenges, but can provide quantitative MR tissue parameter information in addition to volume and thickness measurements.Although bSSFP provides useful contrast, it is highly sensitive to variations in the main magnetic field. This results in dark bands of signal null across an image referred to as banding artifacts. There are a few new methods for mitigating this artifact. An analysis of banding artifact reduction methods is presented in this dissertation. The new methods are shown to be better than traditional methods at reducing banding artifact. However, they do not provide as of high signal to noise ratio as traditional methods in most cases. This analysis is helpful in obtaining artifact free images for volume and thickness measurements.Image distortion can be created when there is a magnetic susceptibility mismatch between bordering substances being imaged, like in the sinuses where air and body tissues meet. A map of the main magnetic field variation can be used to fix this distortion in post processing. A novel method for obtaining a map of the main magnetic field variation is developed using bSSFP in this dissertation. In cases where bSSFP contrast is desirable this map can be obtained with no additional scan time.A new way to sift out MR tissue parameters: T2, T1, and M0 is presented in this dissertation using bSSFP. This method obtains biomarkers that can potentially show the presence of Osteoarthritis before cartilage degeneration begins at the same time as anatomical images. Adjunct scans do not need to be run to get these extra parameters saving scan time. Unlike many adjunct scans, it is also resolution matched to the anatomical images.

No description available.

Securing a computer from unwanted intrusion requires astute planning and effort to effectively minimize the security invasions computers are plagued with today. While all of the efforts to secure a computer are needed, it seems that the underlying issue of what is being secured has been overlooked. The operating system is at the core of the security issue. Many applications and devices have been put into place to add layers of protection to an already weak operating system. Security did not used to be such a prominent issue because computers were not connected 24/7, they used dialup and did not experience the effects from connecting to multiple computers. Today computers connect to high speed Internet and seem useless without access to email, chat, Internet, and videos. This interconnectedness of computers has allowed the security of many computers to be compromised because they have not been programmatically secured. The core component of computer security might best be done through security layers protecting the operating system. For this research, those who work in the computer field were asked to complete a survey. The survey was used to gather information such as the security layers and enhancements implemented on Linux computers and networks their surrounding network. This research is a stepping stone for further research as to what can be done to further improve upon security and its current implementations. / Securing a computer from unwanted intrusion requires astute planning and effort to effectively minimize the security invasions computers are plagued with today.

Due to changes which are occurring in the information technology sector, the way businesses are being carried out and also the development of the Internet. I have set out in this dissertation to identify the perception of customers regarding Internet as a promotional medium. Primarily, I set out to give an overview of marketing issues related to promotion, issues including the customer's perception, buying influences and the decision process, placing a highlight on the marketing mix influences particularly on promotion. I proceeded by giving an outline of the e- commerce and e-business, identifying the different categories within e-commerce, the steps involved in developing e-business within an organisation. The study identified a number of findings related to the perception of customers regarding the Internet as a promotional medium. Some of the most relative findings indicate that customers still perceived the traditional method of advertising as the best type. A positive feedback has been received regarding the Internet as a marketing tool but there seems to be a lack of trust, which has to be dealt with by companies to make customers overcome this obstacle. Finally customers feel that the human interaction is an important element which has to be made present on website.Companies have to do their best to make utmost use of latest technologies and developments, such as the Internet, so as to maximise organisations goals. To do this the whole organisation has to be committed and the implementation has to be a comprehensive one. Furthermore companies have to ensure that such a development should be used not only to communicate to the customers, but with the customers, benefiting from their feedback.

Following the end of the colonial period, Latin America became a thriving market for goods from the industrializing world, particularly the United States, Great Britain, and France. This thesis explores the sociocultural implications of importation into Mexico City and Caracas, Venezuela, situating the flow of commodities within cultural processes. It analyzes how ordinary people in the two cities interacted with goods from abroad. While most studies of this phenomenon focus on elites, this research suggests that they did not comprise the only group to desire, acquire, and display imported commodities. In Mexico City, non-elites could achieve upward mobility by displaying European items. In Caracas, powerful external commercial ties allowed city residents of most classes to obtain foreign commodities and construct their identity by way of them. Thus, people throughout the social strata associated with imported goods, leading to internal and external effects on cultural identity. / Tinker Foundation / University of North Carolina at Chapel Hill

Ultrasound can be used to create free radicals by growth and collapse of cavitation bubbles. These free radicals have potential use in various fields. The formation of free radicals can be monitored by decrease in T1 during NMR experiments due to paramagnetic effects. Our goal is to develop a method in which ultrasound is used to enhance NMR. By irradiating the sample during analytical measurements, we can decrease T1 which can be used as a non-toxic contrast agent1 producing hydroxyl radicals from the water in the body, invoke NMR enhancement using dynamic nuclear polarization2, control and understand polymer reactions3,4, and study the formation of radicals in chemical systems with EPR5. The experiments conducted indicated a decrease in T1 when ultrasound was applied. A maximum decrease was observed when 104 W of ultrasound power was applied and with higher concentrations of radical producing species. Through the experiments it was evident that the sample temperature increased during sonication. To counter this, gated sonication was used to minimize temperature increase. During sonication, the sample was vigorously mixed. Experiments where the sample was mixed through alternate means and theoretical simulations indicate that sample mixing gives an apparent decrease in T1. In situ sonication to decrease T1 shows promise. The question remains if the decrease is due to a combination of radical production and mixing or just an artifact of sample mixing. This is a difficult parameter to determine but future experiments will attempt to supply further conclusions. / Master of Science

Diese Doktorarbeit befasst sich mit der methodischen Entwicklung von Akquisition- und Rekonstruktionstechniken zur Anwendung von Echtzeit-Bildgebungstechniken auf das Gebiet der dynamischen kontrastmittelgestützten Magentresonanztomographie. Zur Unterdrückung unerwünschter Bildartefakte wird eine neue Spoiling-Technik vorgeschlagen, die auf randomisierten Phasen der Hochfrequenzanregung basiert. Diese Technik erlaubt eine schnelle, artefaktfreie Aufnahme von T1-gewichteten Rohdaten bei radialer Abtastung. Die Rekonstruktion quantitativer Parameterkarten aus solchen Rohdaten kann als nichtlineares, inverses Problem aufgefasst werden. In dieser Arbeit wird eine modellbasierte Rekonstruktionstechnik zur quantitativen T1-Kartierung entwickelt, die dieses inverse Problem mittels der iterativ regularisierten Gauß-Newton-Methode mit parameterspezifischer Regularisierung löst. In Simulationen sowie in-vitro- und in-vivo-Studien wird Genauigkeit und Präzision dieser neuen Methode geprüft, die ihre direkte Anwendung in in-vitro-Experimenten zur "first-pass"-Perfusion findet. In diesen Experimenten wird ein kommerziell verfügbares Phantom verwendet, dass in-vivo-Perfusion simuliert und gleichzeitig vollständige Kontrolle über die vorherrschenden Austauschraten erlaubt.