Thesis (M.Sc.D.)--Boston University, School of Graduate Dentistry, 1975. Periodontology. / Includes bibliographic references: leaves 112-131. / One hundred-twenty subjects were assigned to AP-100 enzyme mouthwash, used twice daily, in a doubleblind treatment schedule for six weeks. They were divided equally into Part A and Part B, sixty subjects each. In Part A, subjects ,vere scored, then half of them were randomly assigned to placebo and half to AP-100 enzyme. Removal of pre-existing plaque and treatment of gingivitis only were considered in this part. Part B, focused on reducing plaque accumulation and treatment of gingivitis. Therefore, all subjects in Part B underwent complete prophylaxis with a base line score equal to zero. Gingivitis only was scored in this group and the subjects were randomly assigned half to AP-100 and the other half to placebo. Plaque and gingivitis were scored at three and six weeks. [TRUNCATED]

"This thesis presents an ultrasound technique for measuring the absolute integrated backscatter (IBS) of arterial wall structures through an intervening inhomogeneous soft tissue layer. The aberrating effect of this tissue layer is minimized by normalizing the measured IBS from the wall region of interest with the IBS from an adjacent range cell in blood. The technique may become a tool to differentiate between stable and vulnerable plaques in the carotid artery."

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Master of Dental Surgery / This work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au

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Atherosclerotic plaques with high probability of rupture show the presence of a hot spot due to the accumulation of inflammatory cells. This study utilizes two and three dimensional (2-D and 3-D) arterial geometries containing an atherosclerotic plaque experiencing different levels of inflammation and uses models of heat transfer analysis to determine the temperature distribution in the plaque region. The 2-D studies consider three different vessel geometries: a stenotic straight artery, a bending artery and an arterial bifurcation which model a human aorta, a coronary artery and a carotid bifurcation, respectively. The 3-D model considers a stenotic straight artery using realistic and simplified geometries. Three different blood flow cases are considered: steady-state, transient state and blood flow reduction. In the 3-D model, thermal stress produced by local inflammation is estimated to determine the effect of inflammation over plaque stability. For fluid flow and heat transfer analysis, Navier-Stokes equations and energy equation are solved; for structural analysis, the governing equations are expressed in terms of equilibrium equation, constitutive equation, and compatibility condition, which are are solved using the multi-physics software COMSOL 3.3 (COMSOL, Inc.). Our results indicate that the best location to measure plaque temperature in the presence of blood flow is recommended between the middle and the far edge of the plaque. The blood flow reduction leads to a non-uniform temperature increase ranged from 0.1 to 0.25 oC in the plaque/lumen interface. In 3-D realistic model, the multiple measuring points must be considered to decrease the potential error in temperature measurement even within 1 or 2 mm at centerline region of plaque. The most highly thermal stressed regions with the value of 1.45 Pa are observed at the corners of lipid core and the plaque/lumen interface. The mathematical model developed provides a tool to analyze the factors affecting heat transfer at the plaque surface. The results may contribute to the understanding of the relationship between plaque temperature and the likelihood of rupture, and also provide a tool to better understand arterial wall temperature measurements obtained with novel catheters.

Vulnerable plaque is a clinically silent condition of atherosclerotic plaque that leaves a large number of patients at risk of a coronary event. A method to detect vulnerable atherosclerotic plaque would greatly enhance the ability of clinicians to diagnose and treat patients at risk. Fluorescence lifetime imaging microscopy (FLIM) offers a way to extract both spatial and biochemical information from plaque by taking several wide-field images over time. The goal of this study was to determine the potential of a FLIM angioscopy system to detect and differentiate coronary atherosclerotic plaques ex-vivo into several groups including thin, fibrotic, lipid-laden, thick-cap fibroatheroma (FA), and fibrocalcified. Samples were extracted post-mortem weekly and sliced open to have their lumens imaged. For each sample, 51 time resolved wide-field images were taken over 10 nanoseconds at 390 (±40) nm, 450 (±40) nm, and 550 (±88) nm wavelengths. To analyze the samples, the intensity map and lifetime map were created at each wavelength. The intensity map was simply the wide-field images summed in time and normalized. In order to calculate lifetime at each point, a fast, model-free Laguerre deconvolution algorithm was recently developed for FLIM data analysis and was used. This allowed for fast, efficient estimations of the fluorescence decay curves at each pixel of the FLIM images and facilitated the computation of quantitative parameters describing the fluorescence emission of the tissue, specifically, the relative fluorescence intensity and lifetime at defined emission bands. Statistical analysis on these FLIM derived parameters indicated that the autofluorescence emission of the plaques allows for distinguishing relative plaque thickness: thin plaque, whose signal is dominated by elastin fluorophores, shows a marked difference between thicker plaques, such as fibrotic, fibrocalcified and thick-cap FA (who are dominated primarily by collagen). However, the ability of the current FLIM system to differentiate vulnerable plaque remains in question due to the absence of thin-cap FA samples. Further work has also been proposed; of primary concern is gathering thin-cap FA plaque samples needed to validate the system’s ability to differentiate vulnerable plaques from other common groupings.

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The goal of this research was to demonstrate the potential of spectral CT for the discrimination of vulnerable atherosclerotic plaques. It was proposed that spectral CT has the potential to identify the presence of specific markers for vulnerable plaques: iron deposits and lipid core. A spectral micro-CT system incorporating the latest Medipix spectroscopic photon- counting detectors was commissioned for this purpose. Using spectroscopic methods developed with this system, it was possible to distinguish the presence of iron deposits and lipid core within ex vivo atherosclerotic plaques. Atherosclerosis or hardening of arteries is a systemic disease of the vessel wall that occurs in the aorta, carotid, coronary and peripheral arteries. It is characterised by the deposition of calcified plaques on the innermost layer of the artery wall. Vulnerable plaques are unstable, prone to rupture and put the person at risk of cardiovascular events and strokes. Factors that may lead to plaque instability are lipid content and iron deposits. This preclinical study is a precursor to the development of a clinical technique that will enable vulnerable atherosclerotic plaques to be identified in vivo prior to treatment or removal. Following a preliminary study on atherosclerotic plaques with a prototype system, the MARS-CT3 spectral micro-CT system incorporating Medipix3 was developed and commissioned for further plaque studies. The spectral CT data sets acquired by this system were assessed visually for morphology and analysed for material composition using a linear algebra method. The results were correlated with photography and histology (the histology is the current gold standard). The presence of iron and lipid can be differentiated from the background soft-tissue using a linear algebra method. However the quantification of iron in the presence of calcium is not currently possible without additional data or constraints. Nevertheless the presence of iron deposits within the plaques can be distinguished in the high resolution MARS-CT images and has been correlated with photographic and histological evidence. Thus, using the high spatial resolution spectral data from MARS-CT, the discrimination of lipid core and iron deposits within ex vivo advanced human atherosclerotic plaques is feasible. This may provide the basis for the development of a clinical technique that will identify vulnerable plaques in vivo by high resolution spectral CT.

Master of Dental Surgery / This work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au