The term“Digital X-ray Imaging" refers to a variety of technologies that electronically capture x-ray images. Once captured the images may be electronically processed, stored, displayed and communicated. Digital imaging has the potential to overcome weaknesses inherent in traditional screen-film imaging, with high detection efficiency, high dynamic range and the capability for contrast enhancement. Image processing also makes possible innovative techniques such as computer-aided diagnosis, tomosynthesis, dual-energy imaging, and digital subtraction imaging. Several different approaches to digital imaging are being studied, and in some cases, have been developed and are being marketed. Common to all these approaches are a number of technological and medical issues to be resolved. One of the technological issues is the optimal pixel size for any particular image sensor technology. In general, the spatial resolution of the digital image is limited by the pixel size. Unfortunately while reducing pixel size improves spatial resolution this comes at the expense of signal to noise ratio (SNR). In a scintillator-charge-coupled device (CCD) system, the signal can be increased by improving the efficiency of the scintillator or by reducing noise. This study used a very low noise CCD to determine if image quality, as indicated by the modulation transfer function (MTF), the noise power spectrum (NPS) and the detective quantum efficiency (DQE), could be maintained while reducing pixel size. Two scintillators, one a commonly used radiographic screen the other a thallium doped cesium iodide scintillator, were used and the results compared. The results of this study show that image quality can be maintained as pixel size is reduced and that high DQE can be attained and maintained over a wide range of spatial frequencies with a well designed scintillator.

Retinal hypoxia is associated with many retinal diseases, such as diabetic retinopathy. Current retinal research suggests that retinal hypoxia appears prior to the onset of diabetic retinopathy. The preliminary association of retinal hypoxia to the early stages of diabetic retinopathy is stimulating the development of new technologies to measure the oxygen content of retinal tissue. Frequency domain phosphoresence lifetime imaging (PLI) is a promising technology that enables the mapping of the oxygen content across the entire retina in the form of two-dimensional images. The two-dimensional images generated from the PLI process are a spatial mapping of the retinal tissue's oxygen tension. Currently, the phosphorescent based oxygen tension PLI measurements contain contaminating auto-fluorescent signals in addition to the desired phosphorescent signals. These auto-fluorescent signals artificially inflate the oxygen tension readings due to the nature of fluorescent signals in phosphorescent imaging. Additionally, the maps generated through PLI appear to contain oxygen tension information from both the retinal vasculature and the choroidal vasculature. The choroidal vasculature is situated directly behind the retina and can have a different oxygen tension value than the retinal vasculature. This research enhanced the PLI system by mathematically eliminating the contaminating auto-fluorescent signals and investigated the methods aimed at separating the PO2s of the retinal and choroidal vasculature beds. In addition, the application of the enhanced PLI technology to the investigation of retinal oxygen changes in a rat model of type I diabetes yielded results that suggest a hyperoxic to hypoxic trend prior to the onset of diabetic retinopathy.

The material properties of the mitral valve chordae tendineae are important for the understanding of leaflet coaptation configuration and chordal pathology. This research combines basic histology with standard mechanical tests to determine the functioning role of the chordae tendineae during the cardiac cycle. Dual camera stereo photogrammetry was used to measure strains of the chordae in vitro under normal physiologic loading conditions. A uniaxial test simulating the same loading conditions was conducted. Histology and biochemical assays were performed on the chordae to determine chordal microstructure. Six porcine mitral valves were used for the in vitro flow loop study. The maximum strain experienced was 4.29% l 3.43% and was experienced at 249 msec after the start of valve closure. The loading rate was slightly higher than the unloading rate. The anterior lateral strut chordae had a higher maximum strain and loading rate than the posterior medial strut chordae. The posterior medial strut chordae had a higher unloading rate than the anterior lateral strut chordae. Histological examination revealed blood vessels in the chordae. The anterior strut chordae contain significantly more vessels than the other chordae. Different structural levels were observed for all chordae. The inner layer was characterized by a higher concentration of collagen; whereas, the middle layer was collagen with interwoven elastin fibers. The collagen microstructure was characterized by directional crimping. The anterior and posterior marginal chordae contained significantly more DNA than the other chordae (p<0.01). The anterior strut chord was found to contain significantly less DNA than all the other chordae (p<0.01). The collagen assay results showed that the posterior marginal chord contained significantly more collagen than the other chordae (p<0.01). The Fastin Elastin assay results showed no significant difference in the amount of elastin between the chordae. This study demonstrates the first in vitro examination of the strain experienced by the chordae tendineae of the mitral valve. This technique allows the investigation of the behavior of biological tissues under physiologic loading conditions. Contrary to earlier belief, vessels were found in the chordae. The microstructure and biochemical composition of the chordae tendineae is related to their function during coaptation.

This dissertation presents a fully automatic segmentation algorithm for cardiac MR data. Some of the currently published methods are automatic, but they only work well in 2D and sometimes in 3D and do not perform well near the extremities (apex and base) of the heart. Additionally, they require substantial user input to make them feasible for use in a clinical environment. This dissertation introduces novel approaches to improve the accuracy, robustness, and consistency of existing methods. Segmentation accuracy can be improved by knowing as much about the data as possible. Accordingly, we compute a single 4D active surface that performs segmentation in space and time simultaneously. The segmentation routine can now take advantage of information from neighboring pixels that can be adjacent either spatially or temporally. Robustness is improved further by using confidence labels on shape priors. Shape priors are deduced from manual segmentation of training data. This data may contain imperfections that may impede proper manual segmentation. Confidence labels indicate the level of fidelity of the manual segmentation to the actual data. The contribution of regions with low confidence levels can be attenuated or excluded from the final result. The specific advantages of using the 4D segmentation along with shape priors and regions of confidence are highlighted throughout the thesis dissertation. Performance of the new method is measured by comparing the results to traditional 3D segmentation and to manual segmentation performed by a trained clinician.

published_or_final_version / abstract / toc / Computer Science and Information Systems / Master / Master of Philosophy

Manganese has been used as a T₁-weighted MRI contrast agent in a variety of applications. Because manganese ions (Mn²) enter viable myocardial cells via voltage gated calcium channels, manganese-enhanced MRI (MEMRI) is sensitive to the viability and the inotropic state of the heart. In spite of the established importance of calcium regulation in the heart both prior to, and following, myocardial injury, monitoring strategies to assess calcium homeostasis in affected cardiac tissues are limited. This study implements a T₁-mapping method to obtain quantitative information both dynamically and over a range of MnCl₂ infusion doses. In order to optimize the current manganese infusion protocols, both dose dependent and temporal washout studies were performed. A non-linear relationship between infused MnCl₂ solution dose and increase in left ventricular free wall relaxation rate (∆R₁) was observed. Control mice also exhibited significant manganese clearance over time, with approximately 50% decrease of ∆R₁ occurring in just 2.5 hours. The complicated efflux time dependence possibly suggests multiple efflux mechanisms. Using the measured relationship between infused MnCl₂ and ∆R₁, absolute Mn concentration ICP-MS data analysis provided a means to estimate the absolute heart Mn concentration in vivo. We have shown that this technique has the sensitivity to observe or monitor potential Ca²+ handling alterations in vivo due to the physiological remodeling following myocardial infarction. Left ventricular free wall ∆R₁ values were significantly lower (P = 0.005) in the adjacent zone, surrounding the injured myocardial tissue, than healthy left ventricular free wall tissue. This inferred reduction in Mn concentration can be used to estimate potentially salvageable myocardium in vivo for future therapeutic treatment or evaluation of disease progression.

In the last fifteen years, a great deal of effort has been put forth, worldwide, for investigating and enhancing various aspects of optical coherence tomography (OCT). This thesis begins with a description of the technique of OCT, and an analysis of its underlying theory. The design and construction of an OCT system is described, with particular emphasis on a novel delay scanning method, and novel signal processing. Application of OCT to non-destructive characterisation of seeds, examination of skin lesions, measurement of fluid flow, and refractive index determination, are then demonstrated. Two technological enhancements to OCT are presented in this thesis. The first, an extended-range Fourier domain optical delay line (FDODL), extends the scan range of the traditional FDODL by a factor of almost 9, by scanning the galvanometer mirror around the region of zero tilt-angle. Polarisation optics are used to prevent light coupling back into the interferometer after only a single pass through the FDODL. A non-coplanar version of the FDODL is also presented, which overcomes the losses associated with the polarisation-based design, but trades off scan range to do so. Both versions of FDODL demonstrated excellent linearity and scan uniformity. The second technology presented here, bifocal optical coherence refractometry (BOCR), affords OCT the ability to measure refractive indices within turbid media. It achieves this by generating two confocal gates within the sample. From knowledge of the system parameters, and measurements of the confocal gate separation, the refractive index within the medium is evaluated to within ±0.01. Refractive index mapping is then demonstrated in a number of turbid samples. Three other applications of OCT are also demonstrated in this thesis. The first is the use of OCT to measure full thickness in lupin seeds. Although OCT could not penetrate the entire thickness of the hull, it is demonstrated that the variation in thickness of the two layers observed with OCT, explained 81% of the variation in thickness of the entire hull measured under a SEM. OCT was then applied, for what is believed to be the first time, in a large scale seed screening program. The second application is a preliminary investigation of the suitability of OCT to aid in the diagnosis of skin lesions. Although our system did not possess sufficient positioning accuracy to enable a direct one-to-one comparison between OCT and histology, a number of correspondences between OCT and histology images were demonstrated. The final application of OCT demonstrated here is a novel phase-locked-loop based demodulation scheme, to perform Doppler OCT. This demodulation scheme demonstrated a dynamic range of 98dB, a velocity range of ±20mm/s, and velocity resolution of 0.5mm/s. Using this system, laminar flow was demonstrated in milk flowing through a capillary tube.

[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.

Thesis (M. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 130-140). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. "January 1983"--Cover of photocopy. Two p. of original are reproduced on 1 p. of photocopy. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 151-152).