Recent advances in retinal imaging have made it possible to take measurements of retinal oxygen saturation noninvasively in humans. This allows studying the supply of oxygen in healthy and diseased retinae, thereby advancing our understanding of both the normal functioning of the retina and of retinal pathologies. However, retinal oximetry is still a research tool only and requires further improvement before being used in a clinical setting. Here, a single-wavelength flickering light was used to increase retinal blood flow in healthy subjects. This increase is revealed by both vasodilation and an increase in retinal oxygen saturation. A flickering light stimulus provides the means to assess the sensitivity of any retinal oximetry system, as such systems should be able to pick up this increase in retinal blood flow. In addition, the flickering light allows for com- parison to be made within rather than between subjects and can be used to examine the activation of the eye. This reduces the influence of potential confounding factors between subjects including differences in fundus pigmentation and illumination. The most commonly used method to measure retinal oxygenation is the optical density ra- tio (ODR) approach. The standard approach is to compute the average ODR for each vessel segment by combining the hundreds of individual ODR readings and then to use the mean of these segment averages as a measure of oxygen saturation. Alternatively, it has been suggested that the peak location of Gaussian functions fitted to histograms of individual ODR readings can be used as an measure of retinal oxygenation. In response to a 10Hz flickering light, the venular diameter increased by 3.44% (SEM: ±0.53%) (n=16, p<0.05) and the arteriolar diameter by 1.87% (±0.72 %) (p<0.05). The optical density ratio, measured with the Gaussian fit, decreased in the venules from 0.713 (±0.015) to 0.694 (±0.015) (p<0.05). No changes in arteriolar optical density ratios were measured. The post-flicker measurement was computed as the average of up to four post-flicker datasets obtained at 10s, 20s, 30s and 40s after onset of flickering. These results suggest that the flickering light increased retinal blood flow. The mean absolute percentage error was lower in venules for the Gaussian fit method than for the gold standard method for datasets taken at 30s and 40s after onset of flickering. Thus, the Gaussian fit method was more robust. All measurements were taken with a custom-made retinal oximeter. The pixel intensity of the blood vessel and the intensity on either side of the vessel had to be extracted to compute the individual optical density ratios. This required the automatic extraction of the retinal vasculature. Two such algorithms were developed and applied to two databases of retinal fundus images: the DRIVE and the novel DR HAGIS database. One algorithm was purely based on the pixel intensities, while the other made use of oriented Gabor filters. These two algorithms segmented the images to a similar accuracy (DRIVE: 94.56% and 94.54%, DR HAGIS: 95.83% and 95.71% for the intensity and Gabor filter based algorithm, respectively) and performed as well as a human expert (DRIVE: 94.73%). These algorithms were of sufficient quality to extract individual segments for the oximetry study and to align fundus images.

The content of this work is the analysis of retinal vessels pulsation of video sequences acquired by experimental fundus camera based on measuring the brightness profile of the vessel. The first level of analysis in this work is the segmentation of blood vessels and diameter measurement of blood vessels during the sequence. The work contains research methods dealing with the diameter measurement and evaluation of pulsation and analysis segmentation methods using for analysing the vasculature of the retina. From these methods, a vessel tracking method was selected. In segmented video sequences is on the ground of intensity profiles analysed vessel pulsation. Analysis is also made on original dataset and results are discussed considering the frequency characteristic.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第19027号 / 農博第2105号 / 新制||農||1030(附属図書館) / 学位論文||H27||N4909(農学部図書室) / 31978 / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 大澤 晃, 教授 髙部 圭司, 教授 北島 薫 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The knowledge of blood vessel biomechanics is used for understanding and developing treatments for cardiovascular disease. The objective of this project was to develop an experimental protocol, for education and research, that separates active diameter response from the passive, as a function of the intraluminal pressure in a pressure myograph. The design process was performed in three steps. First the protocol was designed for an artificial vessel and then expanded to include passive properties of blood vessels, finally further developments needed to analyze active blood vessels were suggested. The system was built as a pressure myograph containing a vessel chamber where the vessel was mounted on two cannulas, two pressure sensors for calculating the intraluminal pressure, and one microscope equipped with a camera for diameter observations. Reference data for the artificial vessel material was acquired from a uniaxial tensile test. The results was in the form of stress-stretch relations. Both the results from the artificial vessel and the passive blood vessel was in a acceptable reference range. The results indicate that the experimental protocol can be used for testing passive properties of both artificial vessels and small blood vessels. No results were obtained for active blood vessels, thus the experimental protocol can not be used for separating the active response to diameter change of blood vessels. However, further developments of the experimental protocol are discussed. / Kunskap om blodkärlens biomekanik används för att förstå och utveckla behandlingsmetoder mot hjärt- och kärlsjukdomar. Syftet med det här projektet var att utveckla ett experiment som mäter små blodkärls diameter och vätsketryck in vitro. Experimentet skulle sedan separera det aktiva muskelbidraget till diameterförändring från det passiva bidraget. Genom att göra detta kan kunskapen om biomekaniken hos blodkärl utvecklas inom såväl forskning som utbildning. Experimentet utvecklades i tre steg. Först utvecklades det för artificiella blodkärl och anpassades sedan för passiva blodkärl. Slutligen diskuteras vidareutvecklingar av experimentet gällande de aktiva egenskaperna för blodkärl. Experimentet utformades genom att ett kärl placerades i en kammare. Blodkärlet fästes i vardera ände på varsin kanyl som var kopplade till trycksensorer. För att registrera diametern placerades kammaren under ett kameramikroskop. Resultatet består av spänning-sträcknings diagram. Både resultatet för det artificiella blodkärlet och det passiva blodkärlet var inom ett godkänt referensintervall. Dessa resultat stödjer antagandet att experimentet kan användas för att studera passiva egenskaper av artificiella och verkliga blodkärl med storlek mellan 1.9-4.4 mm i ytterdiameter. Ingen mätdata från aktiva blodkärl kunde samlas in, utan utvecklingskrav på systemet för hantering av aktiva blodkärl har föreslagits.

No description available.

The retina is a highly metabolically active tissue with large demands on the supply of nutrients. Disorders affecting the retina often include some vasculopathy with an impact on retinal circulation. Studies of retinal haemodynamics could thus help to detect, differentiate and diagnose diseases, to monitor changes in disease as well as progression and efficiency of the therapy. The present studies were an attempt to validate and determine the clinical usefulness of a newly developed technique for studying the retinal circulation in human eyes. We used different techniques to evaluate different parameters of retinal circulation. We examined how leukocyte velocity determined with Blue Field Simulation and transit times, mean transite time (MTT) and arterio-venous passage (AVP), and vessel diameter, determined from fluorescein angiograms, together reflects the retinal circulation. MTT was determined with a method based on an Impulse-Response technique, MTTIR. In a study on monkeys we compared our method, together with two conventional methods, with an absolute measurement of retinal blood flow (RBF) determined with labelled microspheres. There was a weak, but not statistically significant, correlation between retinal blood flow and MTTIR (r2 = -0.60, p = 0.06), but no useful correlation between retinal blood flow and either of the other two measures of transit times. In a study on healthy eyes we determined the effect of a physiological provocation, changes in arterial blood gases, on retinal circulation. Breathing pure oxygen or increased level of carbon dioxide in inspired air had no effect on MTT, but oxygen reduced leukocyte velocity and vessel diameter and carbon dioxide increased leukocyte velocity significantly. We concluded that unchanged transit time trough the retinal tissue was not due to a lack of effect of the gas provocation but a result due to concomitant changes in volume and flow. In a study on eyes of patients with diabetic retinopathy we investigated the relation between the extent of retinal circulation changes and the severity of the diabetes retinopathy (DRP). Transit times were relatively unaffected until proliferative DRP (PDRP) developed. In eyes with PDRP both MTTIR and AVP were increased. After panretinal photocoagulation treatment MTTIR returned to normal levels and vessel diameters tended to decrease while leukocyte velocity and AVP remained unchanged. We concluded that the increase in MTTIR in eyes with PDRP is at least partly explained by vessel dilation, causing an increased volume of the retinal vascular bed.

No description available.

No description available.

No description available.

No description available.