Automated measurements of retinal bifurcations

This paper presents an analysis of the bifurcations of retinal vessels. The angles and relative diameters of blood vessels in 230 bifurcations were measured using a new automated procedure, and used to calculate the values of several features with known theoretical properties. The measurements are compared with predictions from theoretical models, and with manual measurements. The automated measurements agree with the theoretical prediction measurements with slightly different bias. The automated method can measure a large number of retinal bifurcations very rapidly, and may be useful in correlating bifurcation geometry with clinical conditions

Reliability vs. Total Quality Cost: part selection criteria based on field data, combined optimal customer and business solution

Most privately owned businesses are formed to generate profits. Every year, manufacturers loose a portion of potential profits on covering warranty claims. To minimize warranty costs companies focus on product quality improvements. In this project real historical warranty data of three electronic sensors have been analyzed. Two-parameter Weibull distribution to measure sensors’ reliability have been used. Monte Carlo simulations have been implemented to calculate Total Quality Costs (TQC). The results show that cost of improved products may have an adverse impact on business profit – the main business objective. It has been demonstrated how reliability and TQC interact with each other and specified optimum business solutions. A new ratio representing combined business and customer objectives was introduced – Quality Cost Ratio (QCR). A new term has been proposed – Excessive Quality Cost (EQC). Improved process of selection parts and materials were proposed

A ribbon of twins for extracting vessel boundaries

This paper presents an efficient model for automatic detection and extraction of blood vessels in ocular fundus images. The model is formed using a combination of the concept of ribbon snakes and twin snakes. On each edge, the twin concept is introduced by using two snakes, one inside and one outside the boundary. The ribbon concept integrates the pair of twins on the two vessel edges into a single ribbon. The twins maintain the consistency of the vessel width, particularly on very blurred, thin and noisy vessels. The model exhibits excellent performance in extracting the boundaries of vessels, with improved robustness compared to alternative models in the presence of occlusion, poor contrast or noise. Results are presented which demonstrate the performance of the discussed edge extraction method, and show a significant improvement compared to classical snake formulations

Accurate methods for manually marking retinal vessel widths

This paper compares two manual measurement techniques for measuring retinal vessel segment widths: the kick-points technique and the edge marking technique. An image set of 164 clear, high-resolution segments was used. The kick-points approach uses kick points marked by observers along interpolated cross-sectional intensity profile graphs; the edge marking method allows observers to nominate the edges on a zoomed-up image, and interpolates edge positions. The edgemarking method provides more precise measurements than the kick-points method, but these are subject to more inter-observer variability; we speculate that this result is due to differing observer perceptions of the edge location

Manual measurement of retinal bifurcation features

This paper introduces a new computerized tool for accurate manual measurement of features of retinal bifurcation geometry, designed for use in investigating correlations between measurement features and clinical conditions. The tool uses user-placed rectangles to measure the vessel width, and lines placed along vessel center lines to measure the angles. An analysis is presented of measurements taken from 435 bifurcations. These are compared with theoretical predictions based on optimality principles presented in the literature. The new tool shows better agreement with the theoretical predictions than a simpler manual method published in the literature, but there remains a significant discrepancy between current theory and measured geometry

Doctor of Philosophy

dissertationMuch has been done to define and characterize the mechanisms that control the fate of multipotent retinal progenitors during eye development, but our understanding of this process is still nascent. The histone methyltransferase complex PRC2 is a key regulator of differentiation during the development of organs such as skin and cortex, but its roles in vertebrate retinogenesis have not been explored. My work focused on investigating the possible involvement of PRC2 in the progression of retinal progenitors from proliferation to differentiation during eye development in Xenopus laevis embryos. In the first chapter, I report the cloning of Xenopus Suz12, and determine its expression pattern during development. Xsuz12 is provided maternally and its expression persists as development progresses, particularly in the developing central nervous system. Comparative analysis of the PRC2 core subunits Xez, Xeed, Xsuz12 and Xrbbp4 suggests that their expression largely overlaps in the nervous system. In the second chapter, I characterize in detail the retinal expression of the PRC2 core subunits, and explore its potential roles during development using a loss of function approach. I show that the transcripts of the PRC2 core subunits are coincidently expressed in retinal progenitors and are downregulated upon retinal differentiation. Surprisingly, I found that the levels of the H3K27me3 mark that is catalyzed by PRC2 greatly increase in terminally differentiated cells. Loss of PRC2 function led to a marked decrease in H3K27me3 in retinal cell types. Blocking the translation of the core subunits Xez or Xsuz12 caused a reduction in eye size, inhibition of differentiation genes and a bias toward generation of late born cell types. ChIP-seq analysis on whole embryos revealed that H3K27me3 transiently and selectively decorates a subset of genes expressed in the eye, some of which are known negative regulators of retinal differentiation. In the third chapter, I characterize the expression pattern of the newly identified binding partner of PRC2, Xjarid2, in the developing nervous system of Xenopus and found that it is particularly expressed in differentiated cells. Preliminary loss of function analysis suggests that Xjarid2 is required for neural differentiation, in agreement with data on PRC2 core subunits. Taken together, my data indicate that the PRC2 complex is an important regulator of retinal neurogenesis in Xenopus and highlights the contribution of histone methylation to the regulation of retinal proliferation and differentiation

An active contour model for segmenting and measuring retinal vessels

This paper presents an algorithm for segmenting and measuring retinal vessels, by growing a "Ribbon of Twins" active contour model, which uses two pairs of contours to capture each vessel edge, while maintaining width consistency. The algorithm is initialized using a generalized morphological order filter to identify approximate vessels centerlines. Once the vessel segments are identified the network topology is determined using an implicit neural cost function to resolve junction configurations. The algorithm is robust, and can accurately locate vessel edges under difficult conditions, including noisy blurred edges, closely parallel vessels, light reflex phenomena, and very fine vessels. It yields precise vessel width measurements, with sub-pixel average width errors. We compare the algorithm with several benchmarks from the literature, demonstrating higher segmentation sensitivity and more accurate width measurement

REVIEW - A reference data set for retinal vessel profiles

This paper describes REVIEW, a new retinal vessel reference dataset. This dataset includes 16 images with 193 vessel segments, demonstrating a variety of pathologies and vessel types. The vessel edges are marked by three observers using a special drawing tool. The paper also describes the algorithm used to process these segments to produce vessel profiles, against which vessel width measurement algorithms can be assessed. Recommendations are given for use of the dataset in performance assessment. REVIEW can be downloaded from http://ReviewDB.lincoln.ac.uk

A speech recognition model based on tri-phones for the Arabic language

One way to keep up a decent recognition of results- with increasing vocabulary- is the use of base units rather than words. This paper presents a Continuous Speech Large Vocabulary Recognition System-for Arabic, which is based on tri-phones. In order to train and test the system, a dictionary and a 39-dimensional Mel Frequency Cepstrum Coefficient (MFCC) feature vector was computed. The computations involve: Hamming Window, Fourier Transformation, Average Spectral Value (ASV), Logarithm of ASV, Normalized Energy, as well as, the first and second order time derivatives of 13-coefficients. A combination of a Hidden Markov Model and a Neural Network Approach was used in order to model the basic temporal nature of the speech signal. The results obtained by testing the recognizer system with 7841 tri-phones. 13-coefficients indicate accuracy level of 58%. 39-coeefficents indicates 62%. With Cepstrum Mean Normalization, there is an indication of 71%. With these small available data-only 620 sentences-these results are very encouraging

Study of the dislocation and the changes of the vessels before diabetic retinopathy

One of the main challenges remains the understanding of the diabetes effect in hemodynamic functionality (blood flow, oxygen perfusion etc.) and vascular geometric adaptation before the first lesions of diabetic retinopathy appear. Crucial and Important part is the study of the progress of diabetes through the screening program. Multiple images of the same patient are useful in order to understand the progress by comparing these images either by taking vascular measurements or/and using registration algorithms