The Method Of 3D Reconstructing Of Retina Veins Based On Ocular Fundus Images

The development of computer graphics and image technology has contributed to wide application of 3D medical imaging technology in medical diagnosis and treatment, as is the research focus at present. 3D medical images provide strong evidence for clinic diagnosis, therapy options, curative effects investigation, prognosis measurement and pathogenic mechanism exploration. They also play an enormous role in operation planning and simulation, anatomy, education and medical research. Ocular fundus images are an objective standard for diagnosis. Many diseases, such as diabetes, leukaemia, hypertension, arteriosclerosis and the like, can be diagnosed and treated using the images. It has been proved that application of 3D ocular fundus images makes medical examination sharper and more effective, which provides evidence for clinic diagnosis, therapy options, curative effects investigation, prognosis measurement and pathogenic mechanism exploration. Based on those former researches, this thesis brings forward a way of 3D reconstruction of retina veins and puts it to realization, and it will be a practical guide for future project of ocular fundus images processing.First, the thesis discusses image-based modeling technique, a technique that uses images to reconstruct geometric models of an object. According to the amount of images resources required for modeling, modeling can be divided into the single-imaged and the multi-imaged. This thesis is aiming at a specific issue of single-imaged modeling. The two existing means of single-imaged reconstruction of 3D models are as follows: one is the introduction of repository to make full use of accumulated geometric knowledge on reconstruction; the other is to draw in more interaction, namely, the users directly indicate relevant information on images. A typical problem incurred in single-imaged modeling lies in how to restore the physical shapes through chiaroscuro. Its principle is to analyze the vector of the physical surface through the brightness variety on the surface of images, and then to translate it into deep information. Compared with traditional modeling technique, image-based modeling technology is easier, quicker, and more real. Having been extensively applied, the technology is intended to develop more rapidly.Image segmentation is an important component of research on 3D image reconstruction and visualization. The fundus blood vessels are so complicated that only when they are detected can people make a purposeful and selective analysis and display them. After pre-processed, the blood vessels on the images can be separated from other objects and then be used for 3D reconstruction. First, to change color image to grayscale, and then to enforce images. Enforcing images is to strengthen contrast of the images by use if grayscale modification and histogram modification. The main purpose is to make fundus blood vessels appear sharper on the processed images, so as to make better visual effects. Image filtering will remove image noise to fulfill binalization of final images. This thesis briefly introduces the working principle of linear filter, median filter and Wiener filter.Hole filling is able to give removal treatment to some small areas of the filtered binal images. After filling some irrelevant irregular areas around macular area and blood vessels can be removed, so is done to some white disturbing areas. Skeleton detection is to use the corrosion algorithm to transform the vessel contour into vessel skeleton. As regards vessel boundary extraction, the thesis introduces the principles of Roberts arithmetic operator, Sobel operator and Prewitt operator, with focus on how to apply edge map created by edge operator to process the layers of vessels.Detection of fundus blood vessels is key to vessel modeling. It is mainly using the skeleton map to find out vessel alteration, and using contour map to calculate radius of vessel, and analyzing the intersection of the distributed vessels according to edge map. Eyeball is oval, so we can produce the arithmetic formula about the eyeballs and fundus surfaces. By this means, we can get the mapping relations between any spot in 2D fundus image and its corresponding spot in 3D fundus surface, as well as the theoretic support for 3D reconstruction of fundus vessels. By the use of skeleton map, we can put the vessels into several segments for easier management in the future. Utilizing key points, we can give a concise and correct relation to vessel distribution, since those points can outline its basic distribution.Since the skeleton map is formed out of the contour map by means of the corrosion algorithm, the points on the skeleton map can not completely match with the axis of the vessel tree, therefore, it is incorrect to build a vessel model with that as the center line of vessel. We need to make alteration to the key points to make them closer to the axis; meanwhile, the determination of key points presented in this thesis is to adjust key points to the axis of the vessel, and calculate the radius of the vessel. The edge map of the vessels enable us to find out the hierarchy information of vessels at the intersection. This thesis also presents the application of intersection detection to distinguish vessel embranchment from vessel intersection, the upper layer of vessels from the lower layer by use of edge map. It also provides variance algorithm to detect layers of vessels by using fundus grayscale map. To date, we can go on with 3D reconstruction with all these data, including key points, radius of vessels at key points, intersection, the layers of intersection.The first requirement is to calculate the section through the key point and perpendicular to vessel axis. We simply require the section be perpendicular to the flat surface which is perpendicular to our lines of sight, instead of the one exactly perpendicular to the axis. The effect remains the same. Now use the key point as the centre, the radius of vessel as the radius, to make a circle in the section, and the circular section is formed of the vessel wall at key point and the section. With the circles on both ends of a vessel segment, we can outline this vessel segment in form of column vessel. Linking all these segments up, we construct 3D model of the whole retina vein system. We use D3D software of Microsoft to demonstrate vessel system. 3D images are displayed after setting up lights on the location and determining the materials used. By the set-up of coordinate system, we can switch angles to realize 3D display, so that the users can make an all-round observance of the condition of vessels and their distribution.The 3D model of vessels in this thesis can demonstrate clearly the 3D images of fundus vessles. Certainly, it is far from perfect. For example, we can measure the vessel parameter based on the 3D images of vessels and then analyze the alteration of fundus micro-vessels, which is useful for the diagnosis of such diseases as hypertension, heart diseases and all the others that can lead to alteration in vessel diameter.