No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Imaging speed is an important issue in magnetic resonance imaging (MRI), as subject motion during image acquisition is liable to produce artifacts in the image. However, the speed at which data can be collected in conventional MRI is fundamentally limited by physical and physiological constraints. Parallel MRI is a technique that utilizes multiple receiver coils to increase the imaging speed beyond previous limits by reducing the amount of acquired data without degrading the image quality. In order to remove the image aliasing due to k-space undersampling, parallel MRI reconstructions invert the encoding matrix that describes the net effect of the magnetic field gradient encoding and the coil sensitivity profiles. The accuracy, stability, and efficiency of a matrix inversion strategy largely dictate the quality of the reconstructed image. This thesis addresses five specific issues pertaining to this linear inverse problem with practical solutions to improve clinical and research applications. First, for reconstruction algorithms adopting a k-space interpolation approach to the linear inverse problem, two methods are introduced that automatically select the optimal k-space subset samples participating in the synthesis of a missing datum, guaranteeing an optimal compromise between accuracy and stability, i.e. the best balance between artifacts and signal-to-noise ratio (SNR). While the former is based on cross-validation re-sampling technique, the second utilizes a newly introduced data consistency error (DCE) metric that exploits the shift invariance property of the reconstruction kernel to provide a goodness measure of k-space interpolation in parallel MRI. Additionally, the utility of DCE as a metric for characterizing and comparing reconstruction methods is demonstrated. Second, a DCE-based strategy is introduced to improve reconstruction efficiency in real time parallel dynamic MRI. Third, an efficient and reliable reconstruction method that operates on gridded k-space for parallel MRI using non-Cartesian trajectories is introduced with a significant computational gain for applications involving repetitive measurements. Finally, a pulse sequence that combines parallel MRI and multi-echo strategy is introduced for improving SNR and reducing the geometric distortion in diffusion tensor imaging. In addition, the sequence inherently provides a T2 map, complementing information that can be useful for some applications.

Computing equipment is fundamental to modern day simulation. Visualisation systems are often the most important component. These produce a representation of the real world in the form of pixels. These pixels are presented to viewers and/or devices under test. / The real world is mathematically treated as continuous domain. Visualisation systems produce pixels that collectively provide a digital representation of the real world. Hence, there are difficulties with using visualisation systems to represent the real world. / Sampling processes are employed for the production of pixels in visualisation systems no matter what the graphics architecture. Considering scene content, if the sample frequency does not meet or exceed the Nyquist frequency, aliasing or spectral folding will be produced. This aliasing may be both spatial and temporal, and can be analysed in both the spatial and spatial frequency domains. Spatial aliasing manifests itself in the form of image artefacts including scene-dependent noise. Temporal aliasing manifests itself in the form of pixel scintillation. Both forms are detrimental to simulation with the degree of detriment depending on the application. For virtual urban warfare simulation, soldiers may experience motion sickness, depending on the quantity and strength of the image artefacts. For simulation of imaging missile engagements, erroneous performance results may be produced due to false cueing information from inadequate object representation. / The Defence Science & Technology Organisation (DSTO) is developing an imaging infrared missile simulation capability. A core component is production of infrared scenes using a visualisation system. This system is designed to generate the best possible scenes for the visible band of the electromagnetic spectrum, making generation of the infrared equivalent somewhat difficult. For example, colour-shading calculations are designed for the visible domain and encoded into hardware. This makes it difficult to generate infrared scenes since the colour-shading calculations might have to be written from scratch, performed outside the graphics hardware then applied to pixels. This is a secondary problem however. / The primary DSTO requirement is that the missile simulation capability provide for realistic object representations at long-distances. Compared to the equivalent within the visual band of the electromagnetic spectrum, the seeker must be presented with scenes that are characterised by much larger dynamic range, using objects with smaller features of interest. The visualisation system sample frequency is therefore insufficient for accurate generation of infrared scenes since the objects are positioned at distances beyond what may be considering normal operating range. The resultant undersampling produces significant spatial and temporal aliasing, resulting in spatial artefacts and pixel scintillation, increasing with object range. This problem must be addressed before any other since undersampling has the potential to render infrared scenes totally erroneous at longer distances. / This research describes the work that has been completed to address the undersampling problem of infrared scene generation on visualisation systems. The overall aim was to address the problem for two types of objects: hard body objects such as airframes, and dynamic objects such as engine exhaust plumes and off-board aircraft countermeasures. The problem was addressed for both types of objects in both a pre- and post-pixelation manner, i.e. before and after the generation of spatial and temporal artefacts. The outcome has been successful, resulting in new anti-aliasing schemes for infrared scene generation on commercial visualisation systems. / Thesis ([PhDInformationTechnology])--University of South Australia, 2004.

Thesis (PhD)--University of South Australia, 1994

Typescript (Photocopy) / A stereo-viewer is provided ... to facilitate fusing of the three dimensional CT reconstructions and the stereo wire frame models--Pref. v. 2 / Bibliography: leaves [244]-263 / 3 v. : ill ; 30 cm. + 1 viewer (Taylor-Merchant stereopticon 707) in back pocket of vol. 2 / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Dentistry, University of Adelaide, 1990