Over recent years geological, geochemical and geophysical surveys of mid-ocean ridges have revealed a significant degree of along-axis variability not only in seabed morphology, but also in crustal structure, particularly Numerous geophysical surveys of the Valu Fa Ridge, southwest Pacific, have mapped the extent of an axial mid-crustal reflector. This reflector has been interpreted as representing the top of a sill-like melt lens, comprising a high percentage of partial melt, lying at the top of a crustal magma chamber. In 1995, a controlled-source, wide-angle seismic dataset was acquired at the Valu Fa Ridge during RN Maurice Ewing cruise EW9512, to investigate the mid-deep crustal structure at this ridge, and particularly the crustal magma chamber associated with the melt lens beneath the ridge axis. The EW9512 acquisition geometry was primarily two-dimensional in design, and modelling of these 2-D profiles revealed the presence of an axial low velocity zone beneath the melt lens. This low velocity zone is thought to represent a region of crystal mush comprising a much lower percentage of partial melt than is present in the overlying melt lens. Similar structures have been modelled beneath a number of other mid-ocean ridges. The primary aim of this study was to build on this 2-D interpretation by taking advantage of three-dimensional ray coverage in the axial region in order to assess the along-axis continuity of the magmatic system, correlate this to any ridge segmentation apparent in the seabed morphology, and determine if ridge segmentation is related to the magma supply. The 3-D data were analysed using a tomographic inversion technique. The inversion results suggest that the axial low velocity zone may be segmented on a scale of 5-10 km, which correlates with the morphological segmentation of the ridge crest and is believed to reflect episodic magma supply with different ridge segments at different stages of a cycle of magmatic and amagmatic extension. However, three- dimensional ray coverage is not ideal owing to the dominantly 2-D acquisition geometry. Therefore a detailed assessment of data uncertainty and resolution was undertaken to enable a meaningful interpretation of the inversion results in terms of which features have a geological origin and which are artefacts of the inversion process. P-S mode converted arrivals arising from mid-crustal interfaces were also modelled in order to obtain improved geological constraints on the crustal structure than is possible from P-wave studies alone. This modelling indicates that the uppermost crust is pervaded by thin cracks. In addition, techniques were developed for modeling the polarisation of 5-wave arrivals with low signal strength. Application of these methods suggests that the thin cracks have a preferred orientation parallel to the ridge crest on-axis, and oblique to the ridge crest off-axis which is thought to reflect the pattern of southward propagation of the ridge system inferred from regional tectonic and bathymetric studies. Modelling of P-S mode converted arrivals arising from conversion at the top of the melt lens provided additional constraints on the properties of the melt lens. In conjunction with the 3-D tomographic results, this work suggests that the southernmost ridge segment in the study area has recently become magmatically active following a period of amagmatic extension suggested by its morphology, thus providing evidence for episodic melt supply at this ridge. As part of the suggestions for further work, a theoretical investigation of survey resolution was undertaken to test commonly adopted acquisition geometries with a view to optimising the design and cost-effectiveness of future 3-D controlled-source tomographic experiments.

Adaptive optics or numerical restoration algorithms that restore high resolution imaging through atmospheric turbulence are subject to isoplanatic wave-front errors. Mitigating those errors requires that the wave-front aberrations be estimated within the 3D volume of the atmosphere. Present techniques rely on multiple beacons, either natural stars or laser guide stars, to probe the atmospheric aberration along different lines of sight, followed by tomographic projection of the measurements onto layers at defined ranges. In this paper we show that a three-dimensional estimate of the wave-front aberration can be recovered from measurements by a single guide star in the case where the aberration is stratified, provided that the telescope tracks across the sky with non-uniform angular velocity. This is generally the case for observations of artificial earth-orbiting satellites, and the new method is likely to find application in ground based telescopes used for space situational awareness.

M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / Rayleigh wave dispersion curves are used to invert for the group velocity maps of the southwestern block of the Congo craton. The group velocity maps were then inverted to obtain the three dimensional shear-wave velocity of the lithosphere beneath the region. In the process, the adjacent Kalahari craton and Damara mobile belt were also mapped to help constrain the southernmost edge of the Congo craton. To obtain the surface wave group velocity tomography, event-station dispersion curves of Rayleigh waves were measured using the multiple filter analysis method. Then the dispersion curves were inverted using the conjugate gradient least-square (CGLSQR) inversion method. To check the reliability of the result, a checkerboard test was performed. The 2-dimensional group velocities and 3-dimensonal shear-wave velocities were found to be faster beneath the southwestern block of the Congo craton and the Kalahari craton and slower in the Damara mobile belt. The group velocity map at 20s period shows that basins are 0 to 3% slower than PREM model. For longer period (50s to 120s), the Central and East African Rift system are ~ 5 % faster, cratons are 5 to 8% faster, and the adjacent mobile belts are 0 to 4% faster than the PREM model. The Afar depression is the slowest, up to 6% slower than the continental PREM model at all periods. The shear-wave velocity maps reveal that (1) the Afar area is the slowest (up to 8% slower than the IASP91 model), (2) the cratons are faster (up to 6% faster than IASP91) than the surrounding mobile belts (up to 2% faster than IASP91). The East African Rifts system is also slow (up to 5%). The Damara mobile belt constitutes a clear separation terrain between the Congo craton and the Kalahari craton. This result is consistent with previous studies by Pasyanos and Nyblade (2007), and Priestly et al. (2006, 2008), who also found faster shear-wave velocities beneath the Kalahari, Congo and Tanzania cratons. The relatively slow seismic velocities (-1 to 2% compared to IASP91) in the Proterozoic Damara mobile belt between the southwestern block of the Congo craton and the Kalahari craton are explained by the view that the Proterozoic lithosphere has hotter rock materials than the SW block of the Congo craton and the Kalahari craton. Our model of faster lithosphere beneath the SW block of the Congo and the Kalahari craton is also consistent with the model of strongly depleted (in basaltic components) lithosphere beneath these craton; compared to less depleted lithosphere beneath the DMB.

by Ho, Chi-Kin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 62-64). / Chapter 1 --- Introduction / Chapter 2 --- Previous Work --- p.2-1 / Chapter 2.1 --- Thresholding --- p.2-1 / Chapter 2.2 --- Edge Detection --- p.2-2 / Chapter 2.3 --- Region Growing --- p.2-2 / Chapter 2.4 --- Radial Contour Model --- p.2-3 / Chapter 2.5 --- Regularized Region Contrast --- p.2-3 / Chapter 2.6 --- Deformable Model --- p.2-4 / Chapter 3 --- The ODD-Balloons Model --- p.3-1 / Chapter 3.1 --- Design Rationale --- p.3-1 / Chapter 3.2 --- Overview --- p.3-5 / Chapter 3.3 --- 2-D Deformations --- p.3-8 / Chapter 3.4 --- Orthogonal Cut and Volume Transfer --- p.3-11 / Chapter 3.5 --- Smoothing Operation --- p.3-17 / Chapter 3.6 --- Properties --- p.3-20 / Chapter 3.6.1 --- Conformation to 3-D Shape --- p.3-20 / Chapter 3.6.2 --- Noise Sensitivity --- p.3-20 / Chapter 3.6.3 --- Convergence and Efficiency --- p.3-22 / Chapter 3.6.4 --- Easy-to-Use --- p.3-23 / Chapter 3.7 --- Summary --- p.3-24 / Chapter 4 --- Experiment Results --- p.4-1 / Chapter 4.1 --- Synthetic Data Experiments --- p.4-1 / Chapter 4.2 --- Real Data Experiment --- p.4-3 / Chapter 4.3 --- Discussions --- p.4-6 / Chapter 5 --- Conclusion and Future Work --- p.5-1 / Chapter 5.1 --- Conclusion --- p.5-1 / Chapter 5.2 --- Recommended Future Work --- p.5-2 / Appendix A Discrete Implementation of 2-D Deformation --- p.A-1 / Appendix B Choosing Elasticity and Rigidity Coefficients of 2-D Deformation --- p.B-1 / Bibliography --- p.BIB-1

The ionosphere is a dynamic and ionized medium. Specification of the ionospheric electron density is important for radio systems operating up to a few GHz. Such systems include communication, navigation and surveillance operations. Computerized Ionospheric Tomography (CIT) is a technique that allows specification of the electron density in the ionosphere. CIT, unlike medical tomography, has geometric limitations such as uneven and sparse distribution of ground-based receivers and limited-angle observations. The inversion is therefore underdetermined and to overcome the geometric limitations of the problem, regularization techniques need to be used. In this thesis the horizontal variation of the ionosphere is represented using wavelet basis functions. Wavelets are chosen because the ground based ionospheric instrumentation is unevenly distributed and hence there is an expectation that the resolution of the tomographic image will change across a large region of interest. Wavelets are able to represent structures with different scale and position efficiently, which is known as Multi Resolution Analysis (MRA). The theory of sparse regularization allows the usage of a small number of basis functions with minimum loss of information. Furthermore, sparsity through wavelets can better differentiate between noise and actual information. This is advantageous because it increases the efficacy to resolve the structures of the ionosphere at different spatial horizontal scale sizes. The basis set is also extended to incorporate time dependence in the tomographic images by means of three-dimensional wavelets. The methods have been tested using both simulated and real observations from the Global Navigation Satellite System (GNSS). The simulation was necessary in order to have a controllable environment where the ability to resolve different scale structures would be tested. The further analysis of the methods required also the use of real observations. They tested the technique under conditions of temporal dynamics that would be more difficult to reproduce with simulations, which often tend to be valid in quiet ionospheric behaviors. Improvements in the detection and reconstruction of ionospheric structures were illustrated with sparse regularization. The comparison was performed against two standard methods. The first one was based on spherical harmonics in space, whilst the second relied on a time-dependent smoothing regularization. In simulation, wavelets showed the possibility to resolve small-scale structures better than spherical harmonics and illustrated the potential of creating ionospheric maps at high resolution. In reality, GNSS satellite orbits allow satellite to receiver datasets that traverse the ionosphere at a few hundred km per second and hence a long time window of typically half an hour may be required to provide observations. The assumption of an unchanging ionosphere is only valid at some locations under very quiet geomagnetic conditions and at certain times of day. For this reason the theory was extended to include time dependence in the wavelet method. This was obtained by considering two approaches: a time-smooth regularization and three-dimensional wavelets. The wavelet method was illustrated on a European dataset and demonstrated some improvements in the reconstructions of the main trough. In conclusion wavelets and sparse regularization were demonstrated to be a valid alternative to more standard methods.

Small antennas have attracted significant attention due to their prolific use in consumer electronics. Such antennas are highly desirable in the healthcare industry for imaging and implants. However, most small antennas are not highly directive and are detuned when in the presence of a dielectric. The human body can be compared to a series of lossy dielectric media. A novel antenna design, the orthogonal coil, is proposed to counter both of these shortcomings. As loop antennas radiate primarily in the magnetic field, their far field pattern is less influenced by nearby lossy dielectrics. By exciting two orthogonal coil antennas in quadrature, their beams in the H-plane constructively add in one direction and cancel in the other. The result is a small, yet directive antenna, when placed near a dielectric interface. In addition to present a review of the current literature relating to small antennas and dipoles near lossy interfaces, the far field of the orthogonal coil antenna is derived. The directivity is then plotted for various conditions to observe the effect of changing dielectric constants, separation from the interface, etc. Numeric simulations were performed using both Finite Difference Time Domain (FDTD) in MATLAB and Finite Element Method (FEM) in Ansys HFSS using a anatomically accurate high-fidelity head mesh that was generated from the Visible Human Project® data. The following problem has been addressed: find the best radio-frequency path through the brain for a given receiver position - on the top of the sinus cavity. Two parameters: transmitter position and radiating frequency should be optimized simultaneously such that (i) the propagation path through the brain is the longest; and (ii) the received power is maximized. To solve this problem, we have performed a systematic and comprehensive study of the electromagnetic fields excited in the head by the aforementioned orthogonal dipoles. Similar analyses were performed using pulses to detect Alzheimer’s disease, and on the femur to detect osteoporosis.

O pilar do sucesso do tratamento endodôntico é o diagnóstico e, para esse objetivo, a radiografia é um excelente recurso auxiliar, tanto pelo seu custo, como pela facilidade de obtenção. Contudo, ela tem suas limitações, pois trata-se da imagem bidimensional de um objeto tridimensional e daí a dificuldade encontrada no diagnóstico de lesões periapicais, fraturas radiculares e reabsorções dentais. Com o advento e o uso da tomografia computadorizada (TC), a partir de 1972, houve uma melhora na capacidade diagnóstica, com as imagens tridimensionais. Entretanto, a TC helicoidal tem limitações, na Odontologia, pelo seu custo, alta dose de radiação à qual o paciente é submetido pela presença de artefatos metálicos. Com a introdução da tomografia computadorizada na Odontologia, por meio do sistema de aquisição Cone Beam, essas desvantagens foram minimizadas, ocorrendo o aumento da qualidade diagnóstica da imagem tridimensional. O objetivo deste trabalho foi comparar a capacidade diagnóstica da tomografia computadorizada Cone Beam, utilizando o aparelho Accuitomo 3DX com as radiografias periapicais e ortopantomográficas (panorâmicas), em casos de lesões periapicais, fraturas radiculares e reabsorções dentais. Para isso, foram analisadas imagens obtidas por meio da tomografia e pelas técnicas radiográficas periapical e panorâmica de 150 casos clínicos, por dois examinadores calibrados, usando escores préestabelecidos. Os resultados permitiram afirmar que a técnica da tomografia apresentou diferença estatisticamente significante em relação às demais técnicas, no diagnóstico da extensão e localização de lesões periapicais, fraturas radiculares e reabsorções dentais. / Diagnosis is the basis of success of endodontic treatment; radiography is an excellent aid for that purpose, due to both cost and easy achievement. However, it also has limitations, since it is a bidimensional image of a three-dimensional object; this explains the difficulty in the diagnosis of periapical lesions, root fractures and tooth resorptions. The advent and use of computerized tomography (CT) since 1972 improved the diagnostic ability with utilization of three-dimensional images. However, helical CT is limited in Dentistry, due to its cost, high radiation dose and presence of metallic artifacts. These disadvantages were minimized by introduction of the cone beam system in dentistry, which improved the diagnostic quality of three-dimensional images. This study evaluated the diagnostic ability of cone beam computerized tomography using the appliance Accuitomo 3DX, compared to periapical and panoramic radiographs, in cases of periapical lesions, root fractures and tooth resorptions. Images of 150 clinical cases were obtained by tomography and by periapical and panoramic radiographic techniques and evaluated by two calibrated examiners, using pre-established scores. The results revealed that the tomography technique presented statistically significant difference in relation to the other techniques for diagnosis of the extent and location of periapical lesions, root fractures and tooth resorptions.

Durante o século passado, o diagnóstico por imagem na odontologia, foi dominado por radiografias, que são representações bidimensionais de estruturas tridimensionais, com sobreposição e distorções associadas. Com a introdução da tomografia computadorizada cone-beam (TCCB), houve um aumento no interesse por esta tecnologia dado às vantagens, como melhor qualidade de imagem, reconstrução tridimensional, possibilidade de visualização craniofacial, e as doses de radiação mais baixas em comparação com a tomografia computadorizada convencional (TC). A TCCB pode ser aplicada em diversas áreas da Odontologia, tais como: implantodontia, cirurgia, traumatologia, periodontia, endodontia, ortodontia, articulações temporomandibulares. Contudo, os profissionais da saúde devem estar cientes que os avanços tecnológicos terão implicações importantes sobre a prática clínica. Estes mesmos profissionais devem conhecer as indicações, limitações e implicações antes de considerar a utilização de tal equipamento. Sendo assim, o presente estudo pretende analisar, criticamente, a utilização e indicação do exame de imagem TCCB na Faculdade de Odontologia de Bauru USP. Ao mesmo tempo, pretende avaliar quantitativamente o uso deste equipamento em relação ao motivo da solicitação e a área bucal requisitada. / During the past century, the diagnostic for image in the dentistry, was dominated for radiographies, which are bidimensional representation of the tridimensional structure with superposition and distortion associated. With the introduction of cone-beam computed tomography (TCCB), there was an increased interest in this technology due to advantages such as better image quality, three-dimensional reconstruction, ability of craniofacial visualization and lower radiation doses compared with the conventional computed tomography (CT). The TCCB can be applied in various areas of dentistry such as dental implants, surgery, traumatology, periodontics, endodontics, orthodontics, temporomandibular joints. However, health professionals should be aware that technological advances have important implications for clinical practice. These same professionals should know the indications, limitations and implications before considering the use of such equipment. Thus, this study aims to analyze critically the use and indication of imaging examination TCCB in the Bauru Dental School - USP. At the same time, evaluate quantitatively the use of equipment for the purpose of the request.

High quality three-dimensional bioluminescence tomographic (BLT) images, if available, would constitute a major advance and provide much more useful information than the two-dimensional bioluminescence images that are frequently used today. To-date, high quality BLT images have not been available, largely because of the poor quality of the data being input into the reconstruction process. Many significant confounds are not routinely corrected for and the noise in this data is unnecessarily large and poorly distributed. Moreover, many of the design choices affecting image quality are not well considered, including choices regarding the number and type of filters used when making multispectral measurements and choices regarding the frequency and uniformity of the sampling of both the range and domain of the BLT inverse problem. Finally, progress in BLT image quality is difficult to gauge owing to a lack of realistic gold-standard references that engage the full complexity and uncertainty within a small animal BLT imaging experiment. Within this dissertation, I address all of these issues. I develop a Cerenkov-based gold-standard wherein a Positron Emission Tomography (PET) image can be used to gauge improvements in the accuracy of BLT reconstruction algorithms. In the process of creating this reference, I discover and describe corrections for several confounds that if left uncorrected would introduce artifacts into the BLT images. This includes corrections for the angle of the animal’s skin surface relative to the camera, for the height of each point on the skin surface relative to the focal plane, and for the variation in bioluminescence intensity as a function of luciferin concentration over time. Once applied, I go on to derive equations and algorithms that when employed are able to minimize the noise in the final images under the constraints of a multispectral BLT data acquisition. These equations and algorithms allow for an optimal choice of filters to be made and for the acquisition time to be optimally distributed among those filtered measurements. These optimizations make use of Barrett’s and Moore-Penrose pseudoinverse matrices which also come into play in a paradigm I describe that can be used to guide choices regarding sampling of the domain and range.

Computed tomography (CT) imaging enables in vivo assessment of lung parenchyma and several lung diseases. CT scans are key in particular for the diagnosis of 1) chronic obstructive pulmonary disease (COPD), which is the fourth leading cause of death worldwide, and largely overlaps with pulmonary emphysema; and 2) lung cancer, which is the first leading cause of cancer-related death, and manifests in its early stage with the presence of lung nodules. Most lung CT image analysis methods to-date have relied on supervised learning requiring manually annotated local regions of interest (ROIs), which are slow and labor-intensive to obtain. Machine learning models requiring less or no manual annotations are important for a sustainable development of computer-aided diagnosis (CAD) systems. This thesis focused on exploiting CT scans for lung disease characterization via two learning strategies: 1) fully unsupervised learning on a very large amount of unannotated image patches to discover novel lung texture patterns for pulmonary emphysema; and 2) weakly-supervised learning to generate voxel-level localization of lung nodules from CT whole-slice labels. In the first part of this thesis, we proposed an original unsupervised approach to learn emphysema-specific radiological texture patterns. We have designed dedicated spatial and texture features and a two-stage learning strategy incorporating clustering and graph partitioning. Learning was performed on a cohort of 2,922 high-resolution full-lung CT scans, which included a high prevalence of smokers and COPD subjects. Experiments lead to discovering 10 highly-reproducible spatially-informed lung texture patterns and 6 quantitative emphysema subtypes (QES). Our discovered QES were associated independently with distinct risk of symptoms, physiological changes, exacerbations and mortality. Genome-wide association studies identified loci associated with four subtypes. Then we designed a deep-learning approach, using unsupervised domain adaptation with adversarial training, to label the QES on cardiac CT scans, which included approximately 70% of the lung. Our proposed method accounted for the differences in CT image qualities, and enabled us to study the progression of QES on a cohort of 17,039 longitudinal cardiac and full-lung CT scans. Overall, the discovered QES provide novel emphysema sub-phenotyping that may facilitate future study of emphysema development, understanding the stages of COPD and the design of personalized therapies. In the second part of the thesis, we have designed a deep-learning method for lung nodule detection with weak labels, using classification convolutional neural networks (CNNs) with skip-connections to generate high-quality discriminative class activation maps, and a novel candidate screening framework to reduce the number of false positives. Given that the vast majority of annotated nodules are benign, we further exploited a data augmentation framework with a generative adversarial network (GAN) to address the issue of data imbalance for lung cancer prediction. Our weakly-supervised lung nodule detection on 1,000s CT scans achieved competitive performance compared to a fully-supervised method, while requiring 100 times less annotations. Our data augmentation framework enabled synthesizing nodules with high fidelity in specified categories, and is beneficial for predicting nodule malignancy scores and hence improving the accuracy / reliability of lung cancer screening.