Cástor Mariño

Retinal Angiography Based Authentication

Traditional authentication (identity verification) systems, employed to gain access to a private area in a building or to data stored in a computer, are based on something the user has (an authentication card, a magnetic key) or something the user knows (a password, an identification code). But emerging technologies allow for more reliable and comfortable for the user, authentication methods, most of them based in biometric parameters. Much work could be found in literature about biometric based authentication, using parameters like iris, voice, fingerprint, face characteristics, and others. In this work a novel authentication method is presented, and first results obtained are shown. The biometric parameter employed for the authentication is the retinal vessel tree, acquired through a retinal angiography. It has already been asserted by expert clinicians that the configuration of the retinal vessels is unique for each individual and that it does not vary in his life, so it is a very well suited identification characteristic. Before the verification process can be executed, a registration step is needed to align both the reference image and the picture to be verified. A fast and reliable registration method is used to perform that step, so that the whole authentication process takes very little time.

Automatic Extraction of the Retina AV Index

In this paper we describe a new method to approach the diameter of veins and arteries in the retina vascular tree, focusing not only on precision and reliability, but also on suitability for on-line assistance. The performed system may analyze the region of interest selected in the image to estimate the retinal arteriovenous index. This analysis involves two different steps: the blood vessels detection, which extracts the vascular structures present in the image, and the blood vessel measurement, which estimates the caliber of the already located vessels. The method may locate 90% of the structures, giving a reliability of 99% in detection and 95% in measurement.

Topological Active Volumes

In the last years, deformable models raised much interest and found various applications in the field of 2D and 3D computer vision. Active surfaces are usually employed for segmentation and object reconstruction. In this paper, a new model for 3D image segmentation is proposed, the Topological Active Volumes (TAV). This model is based on deformable models, it is able to integrate the most representative characteristics of the region-based and boundary-based segmentation models and it also provides information about the topological properties of the inside of detected objects. This model has the ability to perform topological local changes in its structure during the adjustment phase in order to: obtain a specific adjustment to object’s local singularities, find several objects in the scene and identify and delimit holes in detected structures.

Algorithm for registration of full Scanning Laser Ophthalmoscope video sequences

Fluorescein angiography is an established technique for examining the functional integrity of the retinal microcirculation for early detection of changes due to retinopathy. This paper describes a new method for the registration of large Scanning Laser Ophthalmoscope sequences (SLO), where the patient has been injected with a fluorescent dye. This allows the measurement of parameters such as the arteriovenous passage time. Due to the long time needed to acquire these sequences, there will inevitably be eye movement, which must be corrected prior to the application of quantitative analysis. The algorithm described here combines mutual information-based registration and landmark-based registration. The former will allow the alignment of the darkest frames of the sequence, where the dye has not still arrived to the retina, because of its ability to work with images without a preprocessing or segmentation, while the latter uses relevant features (the vessels) extracted by means of a robust creaseness operator, to get a very fast and accurate registration. The algorithm only detects rigid transformations but proves to be robust against the slight alterations derived from the eye location perspective during acquisition. Results were validated by expert clinicians.

Similarity Metrics Analysis for Feature Point Based Retinal Authentication

Biometrics refer to identity verification of individuals based on some physiologic or behavioural characteristics (face, fingerprint, signature...). The typical authentication process of a person consists in extracting a biometric pattern of him/her and matching it with the stored pattern for the authorized user obtaining a similarity value between patterns. If that similarity is bigger than some threshold the authentication is accepted, otherwise is rejected. Thus, the similarity metrics determine the system ability to successfully classify authentications as authorized or unauthorized. In this work, an analysis of similarity metrics performance is presented for a biometric system in which retinal vessel feature points are used as biometric pattern. The results of the system allow to establish a confidence band for the metric threshold where no errors are obtained for training and test sets.

Retinal based authentication via distributed web application

Traditional authentication systems, employed to gain access to a private area in a building or to data stored in a computer, are based on something the user has (an authentication card, a magnetic key) or something the user knows (a password, an identification code). But emerging technologies allow for more reliable and comfortable for the user, authentication methods, most of them based on biometric parameters. Much work could be found in literature about biometric based authentication, using parameters like iris, voice, fingerprints, face characteristics, and others. We have developed a new methodology for personal authentication, where the biometric parameter employed for the authentication is the retinal vessel tree, acquired through a retinal angiography. It has already been asserted by expert clinicians that the configuration of the retinal vessels is unique for each individual and that it does not vary in his life, so it is a very well suited identification characteristic. In this work we will present the design and implementation stages of an application which allows for a reliable personal authentication in high security environments based on the retinal authentication method.

Segment extraction using burns principles in a pseudo-color fuzzy hough transform

This paper describes a computational framework developed for the extraction of low-level directional primitives present in an image, and subsequent organization through a line segment detector. The system is divided in three stages: extraction of the directional features in the image through an efficient implementation of Gabor wavelet decomposition; reduction of these high dimensionality results by means of a growing cell structure; and extraction of the segments from the image. This last step was first implemented through a pseudo-color Fuzzy Hough Transform and then improved through some principles of the Burns segment detector.

Design of a medical application using XML based data interchange

The recent proliferation of computing devices and the contexts in which they are used demand diversity in distributed applications as well. The objective of our research is the development of a medical framework where information from patients can be accessed from heterogeneous and (possibly) mobile computing environments. Moreover, high availability and reliability are also milestones in that system. The former objective is achieved by using eXtensible Markup Language (XML) for the communication medium, in combination with eXtensible Stylesheet Language (XSL) transformations to allow different kinds of clients access the data. High availability is achieved by using a concurrent and distributed language, Erlang/OTP, for the development on the server side. Also, in the server side, techniques coming from the formal methods area are applied to improve the system design and performance and to ensure the system correctness. And finally, reliability, confidentially and authentication, fundamental items in the data communications, are accomplished by mean of the Secure Socket Layer (SSL) protocol.