Introduction. The use of Functional Magnetic Resonance Imaging (fMRI) in studying central auditory pathways expanded our knowledge of the neurophysiology of hearing. In various studies, an array of diverse auditory stimuli has been used, including pure tones and words, in a "Block" design. Few studies, thus far, have been performed using an event-related design. None of these has used pure tone stimulation. / Subjects and methods. In eight out of 13 subjects enrolled and scanned in this project, data have been acquired and processed. Binaural pure tone stimulation at 2kHz and one higher frequency at 6, 8, or 12 kHz, at 90 dB SPL was presented to all subjects, using a stroboscopic design in an attempt to eliminate cortical response to scanning noise. In addition, an unusually long time of repetition (TR) interval of 10 seconds was utilized. The aim in data processing was to generate: (a) a Peak Height Map (PHM) with selection of areas of stimulation based on the maximal response; (b) a statistical map from the raw data of the images. / Results. No consistent morphology was detected in the BOLD event-related curves, corresponding to the percentage change from baseline over time. Such curves revealed significant oscillation with marked dips below baseline, highly suggestive of an irregular noise pattern. Comparing the curves to each other, no discernible shape or similarities were noted. / Conclusion. Attempting to extract both the temporal and spatial characteristics of the cortical response to pure tone stimuli resulted in a dispersal of data over many parameters, therefore "diluting" it. This, in turn, yielded a negative result where the responses were "drowned" revealing but a noise pattern.

The first goal of this study was to develop experimental tools to estimate the blur and noise characteristics of X-ray CT systems. We evaluated the noise power spectrum (NPS) using the averaged periodogram technique. As predicted by theory, varying the image reconstruction filter produced a shift in the frequency content while slice thickness only affected the amplitude of the noise. / In order to quantify the blur, we developed and evaluated two non-linear parametric models of the point spread function (PSF): the Gaussian and damped cosine models. We fitted these models to images of spatially distributed point sources and thus quantified the pattern of shift-variance. We found that the system produced a rotating blur and observed a loss of PSF radial symmetry as the input point source moved away from the center of the field of view. We validated the use of point sources by comparing non-parametric PSF estimates obtained with this input to those found using a correlation-based technique (Wiener-Hopf equation). We gained insight into the design of the input signal, which consisted of pseudo-randomly located holes, through an exhaustive simulation. / The second goal was to investigate how this information could be used to process CT images. We formulated and evaluated a coordinate transformation for shift-invariant restoration of CT images. We developed a simple evaluation procedure which proved beneficial in delimiting the usefulness and detecting limitations of the method. We also formulated a number of recommendations regarding the use of the threshold and Laplacian of a Gaussian segmentation operators taking the shape of the PSF and of the NPS into account.

The effect of a single exposure of He-Ne laser on collagen content was studied in vivo using laboratory animals. A standardized 1.5 cm full thickness skin incision was made on the dorsum of 24 Sprague-Dawley rats. The rats were divided into six equal size groups, three groups functioning as controls and three groups functioning as experimental. The experimental animals were irradiated with He-Ne laser four days post-incision for 16 minutes to deliver a total dose of 5.99 J/cm$ sp2$. On days 6, 10 and 14 post-incision, control and experimental animals had the healing wounds excised for analysis of collagen content by assaying spectrophotometrically the hydroxyproline content within the tissue samples. / The results of the hydroxyproline content were analyzed using independent-groups t-test and analysis of variance. It was demonstrated that even though the mean values of hydroxyproline within the experimental groups were higher than the respective control groups, no statistical significance could be attributed to this observation.

Quantification of physiological functions with positron emission tomography requires knowledge of the arterial radioactivity concentration. Automated blood sampling systems increase the accuracy of this measurement, particularly for short-lived tracers such as oxygen-15, by reducing the sampling interval to a fraction of a second. They, however, require correction for tracer delay between the arterial puncture site and the external radiation detector (external delay), and for the tracer bolus distortion in the sampling catheter (external dispersion). / We have evaluated and implemented the "Scanditronix" automated blood sampling system and measured its external delay and dispersion. PET studies of cerebral blood flow and oxygen metabolism using simultaneous manual and automated blood sampling were analyzed and compared. We show that the results obtained with automated blood sampling are more reliable than those based on manual sampling. We also present suggestions to further improve the reliability of quantitative PET studies based on automated blood sampling.

The investigation and management of patients with life threatening haemoptysis is a common clinical problem in South African Hospitals. Establishing the aetiology and origin of the haemorrhage and treating these patients is both difficult and expensive in terms of human and financial resources. The purpose of this study was to identify common local aetiologies for severe haemoptysis, review the investigation and treatment of these patients at Wentworth Hospital, Durban and to formulate a plan of management. Retrospective and prospective studies of consecutive patients treated at Wentworth Hospital were performed. In the prospective study a new embolic material gelatin linked acryl microspheres (embospheres) was used for bronchial artery embolization (BAE). The study demonstrated a change in the spectrum of aetiologies of haemoptysis, from bronchiectasis following tuberculosis to destructive pneumonias. The chest radiograph was always the initial imaging investigation but was found to be inaccurate in detecting the origin of the bleeding. High resolution computed tomography of the lungs (HRCT) was the single best investigation to detect the cause and origin of the haemoptysis. HRCT detected focal bronchiectasis and intracavitatory aspergillomas that were undetected on the chest radiograph. Pleural thickening detected on CT was a good indicator of the presence of transpleural collaterals. The major limitation with HRCT was that it could not be performed if the patient was too dyspnoeic to cooperate during the scan. The role of bronchoscopy appears limited in patients with severe haemoptysis to those patients who are potential surgical candidates. I found that bronchoscopy was not accurate in detecting the source of bleeding in the few patients in which it was performed. Bronchial arteriography remains the gold standard in the detecting the source of haemorrhage. Bleeding sites were detected on angiography in the presence of focal hypervascularity, neovascularity and the presence of broncho-pulmonary shunts. Bronchial arteries were hypertrophied in bronchiectasis but were normal in size in some patients who had acute pneumonias. Bronchial artery embolization was the treatment of choice for severe haemoptysis in the patients studied. The use of gelatin cross linked micro spheres has significantly improved the initial success rate following the procedure with less complications compared to the use of polyvinyl alcohol particles (PVA). It is important to identify systemic transpleural collaterals at arteriography and to embolize them to reduce recurrent haemoptysis. Patients with aspergillomas responded well to embolization. Recurrent haemoptysis remains the major limitation of BAE but is reduced with the use of micro spheres as embolic agents and thorough embolization of systemic collaterals on the affected side. Surgical resection was an option for a limited number of patients with focal disease in one lung and good respiratory reserve. The major limitation of the study was the absence of long term follow up to detect those patients with late recurrent haemoptysis. / Thesis (D. Med.)-University of Natal, Durban, 2003.

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Space constraints often present the greatest challenge in determining the lay-out of specific radiotherapy installations. To fulfill these constraints high density concrete is often employed in construction. We have undertaken a study to establish the transmission of primary, leakage and scatter radiation through a particular type of high density concrete. In the course of this study various characteristics of leakage and scatter radiation from a 10 MV linac have also been investigated. The results of these studies are reported in this thesis. / To establish the correct chamber configuration required for the characterization of the transmission factors for primary, leakage and scatter radiation and to determine the scatter-to-incidence dose ratio a, we have measured the build-up curves and verified the validity of the inverse square law for these different radiations. The build-up data for the radiation scattered from a humanoid phantom at different angles from the primary axis have shown that even at low scatter angles little to no build-up is required for scatter radiation measurements.

Atherosclerotic narrowing of the carotid arteries in asymptomatic individuals is associated with an increased risk of cerebrovascular ischemic events. The prevention of stroke in this context requires an understanding of the natural history of cerebrovascular atherosclerosis and the availability of an effective means for the detection and follow-up of carotid stenosis. / Methodological standards for the conduct and reporting of natural history studies of asymptomatic carotid disease are proposed and used to carry out a structured methodological appraisal of the literature. The findings suggest that greater attention should be paid to the design and statistical analysis of natural history studies. / A secondary analysis of the data from a natural history study of asymptomatic carotid disease is undertaken for the purpose of evaluating the prognostic usefulness of repeated duplex ultrasound examinations. Multivariable Cox proportional hazards models with fixed and time-dependent covariates are used to evaluate the predictive ability of carotid stenosis measurements obtained by duplex ultrasound at enrollment and during follow-up. The results of the analysis do not support the use of routine carotid ultrasound in clinical practice to determine prognosis for unselected patients with asymptomatic carotid disease.