The non-invasive cardiovascular imaging modalities, cardiovascular magnetic resonance (CMR) and multi-detector computer tomography (MDCT) are playing an increasing role in both clinical and research settings. CMR is a unique imaging modality due to unsurpassed contrast between soft tissue structures that is non-invasive, does not use ionising radiation and is able to provide high-resolution information about cardiac anatomy, function, flow, perfusion, viability and metabolism. It has provided the gold standard in imaging in congenital heart disease. Recent advances in this technology have led to images of high spatial and temporal resolution that has made the characterisation of atheroma possible. While currently spatial resolution still limits its ability to characterise atheroma in native human coronary arteries in living patients, CMR imaging of the coronary arteries has future potential with further technological and sequence advances. MDCT has been used in clinical settings to measure of the amount of calcification in the coronary arteries with “coronary artery calcium scoring” of the coronary tree a surrogate marker of atherosclerosis. MDCT has also become the gold standard for angiographic imaging in most arterial beds such as the carotid and peripheral vascular systems. In the coronary arteries in particular, there have been major advances in the accuracy of coronary MDCT angiography, particularly with regards to its negative predictive value, although excessive calcification and blooming artefacts still limit the diagnostic accuracy of the technique for assessing stenotic severity. In this thesis, our aims were to address some specific novel areas advancing the utility of these imaging modalities in two major areas of interest, namely congenital heart disease and atheroma imaging. Our first step was to validate the accuracy and reproducibility of CMR, the main imaging modality we utilised. To achieve this, we assessed MR imaging of cardiac volumes and function in a normal adult Australian population with a specific focus on the reproducibility of the technique. In confirming that this technique in our hands is both accurate and reproducible, we would then be in a position to be able to confidently use this technique in our future chapters. However, more than this, we sought to establish some normal ranges for left and right atrial and ventricular parameters in our local population. This would be crucial background information for us to be able to make comparisons with future studies in patients with congenital heart disease. Having established our technique and reference ranges, we would then explore the two specific issues in the ensuing two chapters using CMR in one area of congenital heart disease, atrial septal defect. Atrial septal defect is the most common congenital heart defect first diagnosed in adults. The traditional method of assessment of these patients and for suitability for ASD closure involves semiinvasive investigation with transoesophageal echocardiography (TOE) for measurement of the defect size and atrial septal margins. MRI assessment of patients prior to percutaneous device closure compared to TOE assessment would provide information on the accuracy of TOE assessment and provide information of the utility of cardiac MRI as an alternative to TOE for the work-up of these patients prior to ASD closure. In our third original research chapter, we utilised CMR to understand the effects of percutaneous ASD closure on cardiac chamber volumes. We achieved this by assessing with cardiac MRI pre-closure and post-closure atrial and ventricular cardiac volumes. Longstanding right heart dilatation in the setting of an ASD may lead to complications including right heart failure, pulmonary hypertension and arrhythmia. Closure of the ASD should reduce right heart volumes by removing left-to-right shunting and lead to normalisation of ventricular volumes. The assessment of atrial volume changes with ASD closure may be important in furthering our understanding in its contribution to arrhythmia. Having assessed the ability of CMR to assess both the ASD dimensions, and therefore suitability for percutaneous closure, as well as the effects of ASD closure on cardiac chamber size, we look in the final two original research chapters to move to another area of research development with these highresolution imaging technologies, atherosclerosis imaging. Two particular areas we wished to focus on included the potential of high-resolution MR imaging to monitor effects of HDL infusion on atherosclerosis, and secondly to explore mechanisms behind limitations in MDCT imaging of atherosclerosis, specifically calcification and blooming artifacts. For assessing the effects of HDL infusion on atherosclerosis, we utilised a cholesterol-fed rabbit model of atherosclerosis. The abdominal aorta of the rabbit is comparable in size to the human coronary artery. Previous work with the rabbit model of atherosclerosis and magnetic resonance imaging of the aortic wall has shown that it can provide information about atherosclerotic composition as well as provide serial data of the arterial wall. While high intensity lipid-lowering with statins remains the first line management of at risk individuals, modest manipulations of serum HDL levels are associated with a significant impact on cardiovascular risk. Thus, we assessed the effect of HDL infusion and atorvastatin in a rabbit model of using MRI aortic atherosclerosis as the endpoint. In our fifth and final original research chapter, we assessed the accuracy of quantification of atherosclerotic calcification with MDCT in the carotid arteries of patients undergoing carotid endarterectomy, and sought to identify algorithms or techniques that may improve quantification of calcification. This would potentially lead to an improvement in the ability of MDCT techniques to quantify stenotic severity in coronary arteries that were calcified. To achieve these we utilised MDCT in vivo and in comparison with carotid endarterectomy specimen micro-CT. Importantly, as part of this study, we undertook a thorough assessment of reproducibility of these techniques. Thus, in summary, we have been able to confirm the accuracy and reproducibility of CMR and MDCT in the areas of a specific congenital defect (ASD) and atherosclerosis imaging, and utilised these techniques to advance our understanding of these disease states. This thesis identifies strengths and weaknesses of these techniques that will allow us to more appropriately use them for future purposes in cardiovascular disease. Future work directly stemming from this thesis has already begun, and now looks to address issues of whether CMR and MDCT may provide complimentary information about atherosclerotic lesions that may benefit outcomes in certain conditions. Specifically the work in this thesis has led to studies commencing in carotid atherosclerosis and saphenous vein graft atherosclerosis and using these imaging techniques to potentially predict adverse future outcomes. / Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2008

The non-invasive cardiovascular imaging modalities, cardiovascular magnetic resonance (CMR) and multi-detector computer tomography (MDCT) are playing an increasing role in both clinical and research settings. CMR is a unique imaging modality due to unsurpassed contrast between soft tissue structures that is non-invasive, does not use ionising radiation and is able to provide high-resolution information about cardiac anatomy, function, flow, perfusion, viability and metabolism. It has provided the gold standard in imaging in congenital heart disease. Recent advances in this technology have led to images of high spatial and temporal resolution that has made the characterisation of atheroma possible. While currently spatial resolution still limits its ability to characterise atheroma in native human coronary arteries in living patients, CMR imaging of the coronary arteries has future potential with further technological and sequence advances. MDCT has been used in clinical settings to measure of the amount of calcification in the coronary arteries with “coronary artery calcium scoring” of the coronary tree a surrogate marker of atherosclerosis. MDCT has also become the gold standard for angiographic imaging in most arterial beds such as the carotid and peripheral vascular systems. In the coronary arteries in particular, there have been major advances in the accuracy of coronary MDCT angiography, particularly with regards to its negative predictive value, although excessive calcification and blooming artefacts still limit the diagnostic accuracy of the technique for assessing stenotic severity. In this thesis, our aims were to address some specific novel areas advancing the utility of these imaging modalities in two major areas of interest, namely congenital heart disease and atheroma imaging. Our first step was to validate the accuracy and reproducibility of CMR, the main imaging modality we utilised. To achieve this, we assessed MR imaging of cardiac volumes and function in a normal adult Australian population with a specific focus on the reproducibility of the technique. In confirming that this technique in our hands is both accurate and reproducible, we would then be in a position to be able to confidently use this technique in our future chapters. However, more than this, we sought to establish some normal ranges for left and right atrial and ventricular parameters in our local population. This would be crucial background information for us to be able to make comparisons with future studies in patients with congenital heart disease. Having established our technique and reference ranges, we would then explore the two specific issues in the ensuing two chapters using CMR in one area of congenital heart disease, atrial septal defect. Atrial septal defect is the most common congenital heart defect first diagnosed in adults. The traditional method of assessment of these patients and for suitability for ASD closure involves semiinvasive investigation with transoesophageal echocardiography (TOE) for measurement of the defect size and atrial septal margins. MRI assessment of patients prior to percutaneous device closure compared to TOE assessment would provide information on the accuracy of TOE assessment and provide information of the utility of cardiac MRI as an alternative to TOE for the work-up of these patients prior to ASD closure. In our third original research chapter, we utilised CMR to understand the effects of percutaneous ASD closure on cardiac chamber volumes. We achieved this by assessing with cardiac MRI pre-closure and post-closure atrial and ventricular cardiac volumes. Longstanding right heart dilatation in the setting of an ASD may lead to complications including right heart failure, pulmonary hypertension and arrhythmia. Closure of the ASD should reduce right heart volumes by removing left-to-right shunting and lead to normalisation of ventricular volumes. The assessment of atrial volume changes with ASD closure may be important in furthering our understanding in its contribution to arrhythmia. Having assessed the ability of CMR to assess both the ASD dimensions, and therefore suitability for percutaneous closure, as well as the effects of ASD closure on cardiac chamber size, we look in the final two original research chapters to move to another area of research development with these highresolution imaging technologies, atherosclerosis imaging. Two particular areas we wished to focus on included the potential of high-resolution MR imaging to monitor effects of HDL infusion on atherosclerosis, and secondly to explore mechanisms behind limitations in MDCT imaging of atherosclerosis, specifically calcification and blooming artifacts. For assessing the effects of HDL infusion on atherosclerosis, we utilised a cholesterol-fed rabbit model of atherosclerosis. The abdominal aorta of the rabbit is comparable in size to the human coronary artery. Previous work with the rabbit model of atherosclerosis and magnetic resonance imaging of the aortic wall has shown that it can provide information about atherosclerotic composition as well as provide serial data of the arterial wall. While high intensity lipid-lowering with statins remains the first line management of at risk individuals, modest manipulations of serum HDL levels are associated with a significant impact on cardiovascular risk. Thus, we assessed the effect of HDL infusion and atorvastatin in a rabbit model of using MRI aortic atherosclerosis as the endpoint. In our fifth and final original research chapter, we assessed the accuracy of quantification of atherosclerotic calcification with MDCT in the carotid arteries of patients undergoing carotid endarterectomy, and sought to identify algorithms or techniques that may improve quantification of calcification. This would potentially lead to an improvement in the ability of MDCT techniques to quantify stenotic severity in coronary arteries that were calcified. To achieve these we utilised MDCT in vivo and in comparison with carotid endarterectomy specimen micro-CT. Importantly, as part of this study, we undertook a thorough assessment of reproducibility of these techniques. Thus, in summary, we have been able to confirm the accuracy and reproducibility of CMR and MDCT in the areas of a specific congenital defect (ASD) and atherosclerosis imaging, and utilised these techniques to advance our understanding of these disease states. This thesis identifies strengths and weaknesses of these techniques that will allow us to more appropriately use them for future purposes in cardiovascular disease. Future work directly stemming from this thesis has already begun, and now looks to address issues of whether CMR and MDCT may provide complimentary information about atherosclerotic lesions that may benefit outcomes in certain conditions. Specifically the work in this thesis has led to studies commencing in carotid atherosclerosis and saphenous vein graft atherosclerosis and using these imaging techniques to potentially predict adverse future outcomes. / Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2008

[Truncated abstract] Hypothesis: There is deficiency in the evidence base and scientific underpinning of existing diagnostic imaging pathways (DIP) for diagnostic endpoints. Objective: a) To carry out systematic review of literature in relation to use of diagnostic imaging tests for diagnosis and investigation of 78 common clinical problems, b) To identify deficiencies and controversies in existing diagnostic imaging pathways, and to develop a new set of consensus based pathways for diagnostic imaging (DIP) supported by evidence as an education and decision support tool for hospital based doctors and general practitioners, c) To carry out a trial dissemination, implementation and evaluation of DIP. Methods: 78 common clinical presentations were chosen for development of DIP. For general practitioners, clinical topics were selected based on the following criteria: common clinical problem, complex in regards to options available for imaging, subject to inappropriate imaging resulting in unnecessary expenditure and /or radiation exposure, and new options for imaging of which general practitioners may not be aware. For hospital based junior doctors and medical students, additional criteria included: acute presentation when immediate access to expert radiological opinion may be lacking and clinical problem for which there is a need for education. Systematic review of the literature in relation to each of the 78 topics was carried out using Ovid, Pubmed and Cochrane Database of Systematic Reviews. ... The electronic environment and the method of delivery provided a satisfactory medium for dissemination. Getting DIP implemented required vigorous effort. Knowledge of diagnostic imaging and requesting behaviour tended to become more aligned with DIP following a period of intensive marketing. Conclusions: Systematic review of literature and input and feedback from various clinicians and radiologists led to the development of 78 consensus based Diagnostic Imaging Pathways supported by evidence. These pathways are a valuable decision support tool and are a definite step towards incorporating evidence based medicine in patient management. The clinical and academic content of DIP is of practical use to a wide range of clinicians in hospital and general practice settings. It is source of high level knowledge; a reference tool for the latest available and most effective imaging test for a particular clinical problem. In addition, it is an educational tool for medical students, junior doctors, medical imaging technologists, and allied health care personnel.

This study is intended to determine the feasiblity of establishing a high-quality, free-standing MR imaging center dedicated to the breast in or about the City of Redlands.

In MR imaging, techniques for acquisition of reduced data (Rapid MR imaging) are being explored to obtain high-quality images to satisfy the conflicting requirements of simultaneous high spatial and temporal resolution, required for functional studies. The term “rapid” is used because reduction in the volume of data acquisition leads to faster scans. The objective is to obtain high acceleration factors, since it indicates the ability of the technique to yield high-quality images with reduced data (in turn, reduced acquisition time). Reduced data acquisition in conventional (sequential) MR scanners, where a single receiver coil is used, can be achieved either by acquiring only certain k-space regions or by regularly undersampling the entire data in k-space. In parallel MR scanners, where multiple receiver coils are used to acquire high-SNR data, reduced data acquisition is typically accomplished using regular undersampling. Optimal region selection in the 3D k-space (restricted to ky - kz plane, since kx is the readout direction) needs to satisfy “maximum energy compaction” and “minimum acquisition” requirements. In this thesis, a novel star-shaped truncation window is proposed to increase the achievable acceleration factor. The proposed window monotonically cuts down the acquisition of the number of k-space samples with lesser energy. The truncation window samples data within a star-shaped region centered around the origin in the ky - kz plane. The missing values are extrapolated using generalized series modeling-based methods. The proposed method is applied to several real and synthetic data sets. The superior performance of the proposed method is illustrated using the standard measures of error images and uptake curve comparisons. Average values of slope error in estimating the enhancement curve are obtained over 5 real data sets of breast and abdomen images, for an acceleration factor of 8. The proposed method results in a slope error of 5%, while the values obtained using rectangular and elliptical windows are 12% and 10%, respectively. k-t BLAST, a popular method used in cardiac and functional brain imaging, involves regular undersampling. However, the method suffers from drawbacks such as separate training scan, blurred training estimates and aliased phase maps. In this thesis, variations to k-t BLAST have been proposed to overcome the drawbacks. The proposed improved k-t BLAST incorporates variable-density sampling scheme, phase information from the training map and utilization of generalized-series extrapolated training map. The advantage of using a variable density sampling scheme is that the training map is obtained from the actual acquisition instead of a separate pilot scan. Besides, phase information from the training map is used, in place of phase from the aliased map; generalized series extrapolated training map is used instead of the zero-padded training map, leading to better estimation of the unacquired values. The existing technique and the proposed variations are applied on real fMRI data volumes. Improvement in PSNR of activation maps of up to 10 dB. Besides, a reduction of 10% in RMSE is obtained over the entire time series of fMRI images. The peak improvement of the proposed method over k-t BLAST is 35%, averaged over 5 data sets. Most image reconstruction techniques in parallel MR imaging utilize the knowledge of coil sensitivities for image reconstruction, along with assumptions of image reconstruction functions. The thesis proposes an image reconstruction technique that neither needs to estimate coil sensitivities nor makes any assumptions on the image reconstruction function. The proposed cartesian parallel imaging using neural networks, called “Composite image Reconstruction And Unaliasing using Neural Networks” (CRAUNN), is a novel approach based on the observation that the aliasing patterns remain the same irrespective of whether the k-space acquisition consists of only low frequencies or the entire range of k-space frequencies. In the proposed approach, image reconstruction is obtained using the neural network framework. Data acquisition follows a variable-density sampling scheme, where low k-space frequencies are densely sampled, while the rest of the k-space is sparsely sampled. The blurred, unaliased images obtained using the densely sampled low k-space data are used to train the neural network. Image is reconstructed by feeding to the trained network, the aliased images, obtained using the regularly undersampled k-space containing the entire range of k-space frequencies. The proposed approach has been applied to the Shepp-Logan phantom as well as real brain MRI data sets. A visual error measure for estimating the image quality used in compression literature, called SSIM (Structural SIMilarity) index is employed. The average SSIM for the noisy Shepp-Logan phantom (SNR = 10 dB) using the proposed method is 0.68, while those obtained using GRAPPA and SENSE are 0.6 and 0.42, respectively. For the case of the phantom superimposed with fine grid-like structure, the average SSIM index obtained with the proposed method is 0.7, while those for GRAPPA and SENSE are 0.5 and 0.37, respectively. Image reconstruction is more challenging with reduced data acquired using non-cartesian trajectories since aliasing introduced is not localized. Popular technique for non-cartesian parallel imaging CGSENSE suffers from drawbacks like sensitivity to noise and requirement of good coil estimates, while radial/spiral GRAPPA requires complete identical scans to obtain reconstruction kernels for specific trajectories. In our work, the proposed neural network based reconstruction method, CRAUNN, has been shown to work for general non-cartesian acquisitions such as spiral and radial too. In addition, the proposed method does not require coil estimates, or trajectory-specific customized reconstruction kernels. Experiments are performed using radial and spiral trajectories on real and synthetic data, and compared with CGSENSE. Comparison of error images shows that the proposed method has far lesser residual aliasing compared to CGSENSE. The average SSIM index for reconstructions using CRAUNN with spirally and radially undersampled data, are comparable at 0.83 and 0.87, respectively. The same measure for reconstructions using CGSENSE are 0.67 and 0.69, respectively. The average RMSE for reconstructions using CRAUNN with spirally and radially undersampled data, are comparable at 11.1 and 6.1, respectively. The same measure for reconstructions using CGSENSE are 16 and 9.18, respectively.

This thesis focuses on the concept of Single Well Imaging (SWI) in which a seismic source and receivers are deployed in a borehole to investigate the surrounding geology. The Uniwell project (1997-1999) was the first attempt to develop the SWI method; it used a fluid-coupled downhole source, which unfortunately generated high amplitude guided waves in the borehole which obscured all other useful information. Initial research work detailed in this thesis focused on removing the high amplitude guided waves, known as tube waves. Two-step source signature deconvolution using first the recorded source signature, and then the tube-wave reflected from the bottom of the well, succeeded in compressing the tube wave. The results were not consistent across all receivers, but there is enough correlation to identify a P-wave. Further work concentrates on using a new technique called Empirical Mode Decomposition to separate the tube-wave mode from the data. This identifies three dominant modes and a possible body wave arrival, but the results are ambiguous due to the inability of the decomposition to focus on the narrow bandwidth of interest. The source signature deconvolution technique can also be used to process real-time vertical seismic profiling (VSP) data down-hole, during pauses in drilling, in what is referred to as a Seismic-While-Drilling (SWD) setup. Results show that the technique is versatile and robust, giving 1 ms precision on first-break picking even in very noisy data. I also apply the technique to normal VSP data to improve both the resolution and the signal-to-noise ratio. A major effort in this thesis is to consider the effect of a clamped downhole source to overcome the tube-wave problem, using a magnetostrictive source. Earlier work established that the use of a reaction mass tended to excite resonances in the tool which caused the transducer to break. A new design for the source was developed in cooperation with colleagues which utilises a hydraulic amplifier design and a low power coded waveform driving method exploiting the time-bandwidth product to extract the signal from the noise. My results show that as the run time increases the resolution improves. With a run length of 80s it is possible to resolve the signal transmitted 50 cm through a granite formation. This analysis led to a revised design of the source to improve its efficiency. I have used finite difference modelling, with a variable grid technique, to compare an ideal explosive source with an ideal clamped source. The fluid-coupled source emits high amplitude tube waves which virtually obscure the body wave, whereas the clamped source emits a clearly identifiable P-wave along with lower amplitude tube waves. This clearly illustrates the advantage of an ideal clamped source. To model the source more accurately the idealwavelet is replaced by the respective recorded source signatures, and the data is then processed by cross correlation with the appropriate signature. The results show that the coded waveform approaches the resolution of the ideal wavelet very well, with all major events being visible. However, the fluid-coupled source performs very poorly with only the highest amplitude tube-wave visible. This work illustrates that by replacing a fluid-coupled source by a clamped source driven by a coded waveform, and by processing the data using cross correlation or signature deconvolution, it is possible to minimise or eliminate tube-wave noise from a SWI survey. It is hoped that the results outlined here will provide the basis for a new SWI method than can be used to prolong the supply of North Sea oil.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / The next-generation commercial imaging satellites will generate data at several times the rate of current systems. To be commercially successful, these systems must have earth stations as sophisticated as the satellites themselves. Space Imaging has worked with E-Systems to exploit technologies developed over four generations of image processing, analysis and application systems to create a modular, standards-based, earth station for commercial use. A Space Imaging Operations Center can be configured in a variety of ways to provide complete, end-to-end, capabilities, from task generation to receipt of downlink, image processing, and product generation. While it is intended primarily for use with imagery from Space Imaging and other commercial satellites, an Operations Center can also accept, process and manage data from land-based, airborne or seaborne collectors. A sophisticated data management product, Mission Server™, handles and routes all data from signal receipt through final product generation. A unique family of data processing applications permit simultaneous manipulation and analysis of integrated map, image, graphic and text data. Online data storage and archiving are provided by the EMASS® family of products. An Operations Center of any size can accept, process and manage data streams of several hundred megabits per second in real time.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Medicine / Master / Master of Philosophy

published_or_final_version / abstract / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy