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A fiber-based linear optical coherence tomography (LOCT) system employing a cost-effective CMOS camera has previously demonstrated high-resolution imaging suitable for retinal screening, including glaucoma monitoring. However, the system’s imaging depth was constrained to approximately 400μm, insufficient for depth imaging of the optic nerve head (ONH), due to limitations imposed by the camera’s sensor size and pixel pitch. To overcome this limitation without replacing the economical and available sensor, we present a modification to the reference arm. By optimizing the utilization of the camera sensor’s vertical dimension, the system achieves an extended imaging depth, enabling the visualization of deeper tissue structures. Validation using an artificial eye model confirms that the modified LOCT system significantly enhances imaging depth while maintaining B-Scan quality. This advancement offers a cost-effective approach to extend the measurement range of LOCT systems, broadening their applicability in retinal imaging without altering the actual imaging sensor.
This paper presents a method for dynamically controlling the gaze movement of patients during ophthalmic examinations, specifically using infrared funduscopy and Optical Coherence Tomography (OCT) to gather retinal information essential for glaucoma screenings. By using the patient's natural eye movements, this system eliminates the need for traditional precise scanning mirrors used in conventional OCT devices, which typically direct the OCT laser beam across the retina to produce A-scans. In this approach, the OCT laser beam remains fixed while the patient is guided to follow a predetermined pattern on a display with their eyes. This method effectively uses the patient’s eye movements to replace the functionality of scanning mirrors. By tracking the position of the eye in real time, the system ensures that the specific areas of the retina are captured. This technique not only provides a cost-effective alternative to traditional OCT systems but also enhances patient comfort by involving them actively in the process, reducing the need to fixate on a single point. During the examination, the system evaluates each measurement point, and the scan patterns can be adjusted if necessary to ensure comprehensive diagnostic data acquisition. The resulting positions are assigned to the OCT A-scans. This allows the optic nerve B-scans typical for glaucoma examinations to be created in the evaluation. The system is characterized by the fact that it enables flexible adjustments to the imaging patterns in real-time, based on which areas of the eye have already been captured and which still require examination. The setup mainly uses commercially available components to create a cost-effective alternative to conventional, often price-intensive diagnostic devices. This method has the potential to be important not only for the improved diagnosis and monitoring of eye diseases, including glaucoma, but also offers prospects for wider application in preventive eye health care.
This project, which is funded by the German Federal Ministry of Education and Research, attempts to improve the accessibility of diagnostic instruments for glaucoma screening. The presented approach aims to realize real-time near-infrared video fundus imaging that enables the use of targeted fixation stimuli to ensure continuous imaging. The integration of near-infrared illumination with a wavelength of 780 nm not only avoids pupil constriction, but also enables mesopic imaging in darkened ambient light, ensuring optimal visualization of the retinal structure. This innovative system achieves nearly reflection-free imaging through polarized illumination with polarization-dependent beam paths. Its primary aim is to capture extensive fundus areas to facilitate correlations with linear optical coherence tomography (LOCT) measurements. In the future, the fundus setup will be integrated into the LOCT setup. In this research project, the primary aim is to generate images of the optic nerve, but it is also possible to carry out examinations of the macula. Unlike from traditional fundus cameras, this system has a controllable screen for generating individual fixation stimuli, which creates continuous eye movements and enables controlled imaging. The main objective is to capture large fundus areas and track eye positions to combine this information with the LOCT measurements A-scan positions, which enables the creation of B-scans with irregular geometries. This approach replaces the need for complex scanning systems by leveraging natural eye movements. The approach can thus be used to detect retinal pathologies in a different way and could therefore be used for more comprehensive diagnostic and scientific applications.
Development of a Linear Optical Coherence Tomography Low-Cost System for Ophthalmic Applications
(2024)
This publication introduces a prototype of a fiber-based linear optical coherence tomography system (LOCT) that can be used for economical retinal screening in ophthalmology. The system uses standard off-the-shelf components to reduce production costs, complexity, and adjustment efforts while providing high-quality imaging of artificial retinal structures. We present the results of A- and B-scans of technical samples and an artificial eye model that was conducted to assess the system’s performance regarding axial resolution, imaging depth, and dispersion compensation. The study’s findings suggest that LOCT is a cost-effective solution for ophthalmology and shows great potential for monitoring the progression of retina-related diseases such as glaucoma or age-related macular degeneration.
For most classes of chains, it is known if these contain locks, but especially for fixed-angle equilateral equiangular obtuse open polygonal chains in 3D, which can be used to model protein backbones, this is unknown. Fixed-angle equilateral equiangular obtuse closed and open polygonal chains can be used to model polymers. For these, it is clear, that locks based on knots exist, but not which chains are generally locked. We therefore examine both open and closed fixed-angle equilateral equiangular obtuse chains. For this purpose, those chains are divided into various subgroups and, depending on the subgroup, other aspects are investigated to show locks. Techniques from knot theory, graph theory, and specifically robot arm reachability and motion planning are combined. Algorithms are developed to create chains in desired configurations and to study them. It is shown why all fixed-angle equilateral equiangular obtuse closed chains are expected to be locked or in rare cases rigid and non-locked, but never non-locked and non-rigid. For fixed-angle equilateral equiangular obtuse open chains it is shown why it is expected that there are open chains that are locked and that the smallest locked open chain has 𝑛=7.
Untersuchung des Verhaltens von Coriolis Massemessern in einer modulierten Zweiphasenströmung
(1999)
Im Rahmen dieser Diplomarbeit wurde, in Zusammenarbeit mit der Fa. Endress & Hauser, ein neuer Versuchsstand zur Durchflussmessung mittels Coriolismassemessgeräten aufgebaut und in Betrieb genommen. Des Weiteren wurde das Verhalten der Messgeräte in einer Zwei-Phasen-Strömung ( Wasser/Luft ) hinsichtlich ihrer Genauigkeit, bei kontrollierter Eindüsung verschiedener Luftvolumina und Massenströmen untersucht.