Pressboard, a high density cellulose-based material used for insulation in high voltage power transformers, exhibits stress relaxation during compressive loading. Investigating the micro-mechanical mechanisms responsible for the relaxation can lead to modifications of the production process to control the behaviour of the material. This investigation can be done using Synchrotron X-ray micro Computed Tomography which provides sufficient temporal and spatial resolutions to capture the stress relaxation process. In the present thesis, a compression rig for in-situ mechanical loading during X-ray micro Computed Tomography was designed and constructed. Local tomography scans with sub-micrometre resolution were obtained at the TOMCAT beamline at the Swiss Light Source, Paul Scherrer Institut, Switzerland. Several fibre segmentation techniques are analysed, together with Optical Flow and Digital Volume Correlation (DVC), methods used for estimating displacement, strain and velocity vector fields. Suitability of the tested methods is evaluated, and it is found that segmentation of individual fibres in a cellulose material of such a high density is probably not possible using currently available segmentation techniques. The movements during relaxation are measurable at the used resolution, and can be estimated using Optical Flow. Further work into correction of image shift due to rig movement between scans, as well as image artefact reduction should allow for measurement and comparisons of displacement during relaxation as well as DVC-computed strain measurements during compression, recreating earlier results.

Optical Coherence Tomography (OCT) is a subsurface imaging technique with many biomedical and industrial applications. In this thesis, we describe our design and implementation of a time domain OCT system. We used this system to obtain OCT images of objects that are important in different applications. We also used an existing quadrature OCT system to obtain both real and imaginary parts of an OCT image. We introduced a new interpretation of OCT images as the 2nd derivative of the scattering potential of an object. To obtain this scattering potential from its 2nd derivative, we implemented a method of definite integration in the spectral-domain. The obtained scattering potential was used to separate the scattering profile from the absorption profile of an object. We applied this new spectroscopic imaging method to quadrature OCT images of different objects.

Objective: To evaluate three-dimensional position of the TMJ condyle within the glenoid fossa in different types of skeletal patterns. Materials and methods: Ninety CBCT images were consecutively selected and divided into skeletal class I, class II and class III. The images were analyzed locating landmarks in the different areas of the condyle and glenoid fossa. All landmarks presented acceptable reliability. The mean results were compared using ANOVA and Bonferroni post-hoc test (p < 0.05). Results: There was a tendency for the anterior joint space to be smaller than the posterior joint space. Statistical analysis, however, evidenced no significant differences between the anterior, superior and posterior joint spaces and the different skeletal patterns or between sides. Conclusion: There was non-concentricity of the condyle for all the groups studied, and no particular direction was statistically significantly favored. It is unclear whether the differences found would be clinically significant, considering anatomical individual variations.

Iterative CT reconstruction algorithms are superior to the standard convolution backpropagation (CBP) methods when reconstructing from a small number of views (hence less radiation), but are computationally costly. To reduce the execution time, this work implements and tests a parallel approach to iterative algorithms using a cluster of workstations, which is a low cost system found in many offices and non-academic sites. A previous implementation showed little speedup because of the significant cost of inter-processor communication. In this thesis, several data partitioning methods are examined, including some image tiling methods that exploit the spatial locality demonstrated by local CT. Using these methods, computation can proceed locally, without the need for inter-processor communication during every iteration. A relative speedup of up to 17 times is obtained using 25 processors, demonstrating that good performance can be obtained running computationally intensive CT reconstruction algorithms on distributed memory hardware.

Characterized by excessive myocardial glycogen deposition, cardiac hypertrophy, frequent cardiac arrhythmias and progressive conduction system disease, the PRKAG2 cardiac syndrome stems from a genetic mutation in the γ2-subunit of AMP-activated protein kinase (AMPK). Although functionally diverse, the main role of AMPK is to modulate cardiac metabolism in response to depleted ATP levels. A comprehensive study of the dysfunctional regulation of AMPK activity involved in the progression of the human PRKAG2 cardiac syndrome is hindered by the limitations of in vitro techniques. Positron emission tomography (PET) imaging with the glucose analogue, FDG, offers a quantitative assessment of myocardial glucose uptake non-invasively. The aim of this thesis was to determine the ability of FDG to detect changes in glucose uptake, storage and metabolism in the heart in relation to AMPK activity and provide insights into the mechanism of PRKAG2 cardiac hypertrophy. To achieve this aim, a transgenic AMPK γ2-subunit Arg302Gln mouse model was evaluated with small animal FDG PET with correlation to biochemical assays of cardiac AMPK activity and the glycogen metabolism pathway. Using the vena cava blood input function, FDG myocardial glucose uptake was reliably assessed in mice for the first time with Patlak modeling. Reduced FDG uptake in the Arg302Gln PRKAG2 mouse model suggested a feedback pathway reducing exogenous glucose uptake due to excessive intracellular glycogen stores. Despite an increase in FDG uptake in the skeletal muscle of the PRKAG2 mutant mice following insulin stimulation, there was no change in cardiac uptake, signifying myocardial insulin resistance. Increased reliance on glucose oxidation by TMZ inhibition of fatty acid oxidation reduced glycogen stores, restored cardiac function and eliminated ventricular preexcitation. The observed reduction in mouse myocardial FDG uptake mirrors the reduction previously observed in the human PRKAG2 patients. The potential now exists to evaluate both progression and therapeutic interventions for the PRKAG2 cardiac syndrome with the transgenic mouse model with translation to the affected patients using FDG cardiac imaging.

The objective of this study is to apply digital image processing (DIP) techniques to optical coherence tomography (OCT) images and develop computer-based non-subjective quantitative analysis, which can be used as diagnostic aids in early detection of dental caries. This study first compares speckle reduction effects on raw OCT image data by implementing spatial-domain and transform-domain speckle filtering. Then region-based contour search and global thresholding techniques examine digital OCT images with possible lesions to identify and highlight the presence of features indicating early stage dental caries. The outputs of these processes, which explore the combination of image restoration and segmentation, can be used to distinguish lesion from normal tissue and determine the characteristics prior to, during, and following treatments. The combination of image processing and analysis techniques in this thesis shows potential of detecting early stage caries lesion successfully.

The LSO scintillator crystal commonly used in PET scanners contains a low level of intrinsic radioactivity due to a small amount of Lu-176. This is not usually a concern in routine scanning but can become an issue in small animal imaging, especially when imaging low tracer activity levels. Previously there had been no systematic validation of simulations of this activity; this thesis discusses the validation of a GATE model of intrinsic Lu-176 against results from a bench-top pair of detectors and a Siemens Inveon preclinical PET system. The simulation results matched those from the bench-top system very well, but did not agree as well with results from the complete Inveon system due to a drop-off in system sensitivity at low energies that was not modelled. With this validation the model can now be used with confidence to predict the effects of Lu-176 activity in future PET systems.

A plethora of anthropological studies have been undertaken on the skull, including many analyses of sexual dimorphism. Sexual dimorphism reflected in the eye orbits has not always demonstrated consistent or reliable results. However, recent studies (Pretorius, Steyn, & Scholtz, 2006; Ji et al., 2010) suggest some positive results utilizing geometric morphometrics to predict sex. Utilizing 97 post-mortem CT (computed tomography) scans, established morphological and metric techniques for sex determination were assessed from 3D rendered models of the crania. In addition, landmark data were collected on the orbital margin to evaluate the accuracy of sex determination using geometric morphometric techniques. Traditional methods demonstrated poor levels of accuracy for prediction of sex, however, utilizing generalised procrustes analysis and discriminant function analysis on 3D landmark data resulted in 94.95% overall accuracy. Application of recent methodological advances, including geometric morphometrics, should continue to be developed as it increases the ability to assess sexual dimorphism which will allow for greater identification of unknown remains.

Obtaining higher depth of imaging is an important goal in Optical Coherence Tomography (OCT) systems. One of the main factors that affect the depth of OCT imaging is the presence of noise. That’s why the study of noise statistics is an important problem. In the first part of this thesis we obtain an empirical estimate of the second order statistics of noise by using a sequence of Time domain (TD) OCT images. These estimates confirm the non-stationary nature of noise in TD-OCT. In the second part of the thesis these estimates are used to design a depth-dependent matched filter to maximize the Signal-to-Noise Ratio (SNR) and increase the Contrast-to-Noise Ratio (CNR) in TD-OCT. By applying our filter to TD-OCT images of both vascular rabbit tissue and a human tooth, both SNR and CNR were increased and a higher imaging depth was achieved.

X-ray computed tomography (CT) polymer gel dosimetry (PGD) is an attractive tool for three-dimensional (3D) radiation therapy (RT) treatment verification due to the availability of CT scanners in RT clinics. Nevertheless, wide-spread use of the technique has been hindered by low signal-to-noise CT images largely resulting from gel formulations with low radiation sensitivity. However, a new gel recipe with enhanced dose sensitivity was recently introduced that shows great promise for use with CT readout. This dissertation describes development of an CT PGD system for 3D verification of RT treatments using the new gel formulation. The work is divided into three studies: gel characterization, commissioning of a multislice CT scanner and investigation of a dose rate dependence observed during gel characterization. The first component of this work examines the dosimetric properties of the new gel formulation. The response of the gel is found to be stable between 15 - 36 hours post-irradiation and excellent batch reproducibility is seen for doses between 0 - 28 Gy. A dose rate dependence is found for gels irradiated between 100 - 600 MU/min, indicating machine dose rate must be consistent for calibration and test irradiations to avoid dosimetric error. An example clinical application is also presented using an IMRT treatment verification that demonstrates the potential of the system for use in modern RT. The second component of this work focuses on commissioning a multislice CT scanner for CT PGD. A new slice-by-slice background subtraction technique is introduced to account for the anode heel effect. Additional investigations show recommendations for optimizing image quality in CT PGD using a single slice machine also apply to multislice scanners. In addition, the consistency of CT numbers across the multislice detector array is found to be excellent for all slice thicknesses. Further work is performed to assess the tube load characteristics of the scanner and develop a scanning protocol for imaging large gel volumes. Finally, images acquired throughout the volume of an unirradiated active gel show variations in CT data across each image on the order of 7 HU. However, these variations are not expected to greatly influence gel measurements as they are consistent throughout the gel volume. The third component of this work examines the dose rate dependence found during gel characterization. Studies using gel vials and 1 L cylinders indicate the response of the gel does not depend on changes in mean dose rate on the order of seconds to minutes. However, the machine dose rate remains, indicating variations in dose rate on the order of milliseconds influence the response of the gel. An attempt is made to mitigate the effect by increasing the concentration of antioxidant in the gel system but results in reduced overall response. Further work is performed to determine if self-crosslinking of one of the gel components contributes to the observed machine dose rate dependence. In summary, this dissertation has significantly advanced the field of gel dosimetry by providing a prototype CT PGD system with enhanced dose resolution for complex RT treatment verification. / Graduate / 0992 / 0495 / 0756 / holly.johnston@utsouthwestern.edu