Distant pulse oximetry based on skin region extraction and multi-spectral measurement

Capturing vital signs, specifically heart rate and oxygen saturation, is essential in care situations. Clinical pulse oximetry solutions work contact-based by clips or otherwise fixed sensor units which have sometimes undesired impact on the patient. A typical example would be pre-term infants in neonatal care which require permanent monitoring and have a very fragile skin. This requires a regular change of the sensor unit location by the staff to avoid skin damage. To improve patient comfort and to reduce care effort, a feasibility study with a camera-based passive optical method for contactless pulse oximetry from a distance is performed. In contrast to most existing research on contactless pulse oximetry, a taskoptimized multi-spectral sensor unit instead of a standard RGB-camera is proposed. This first allows to avoid the widely used green spectral range for distant heart rate measurement, which is unsuitable for pulse oximetry due to nearly equal spectral extinction coefficients of saturated oxy-hemoglobin and non-saturated hemoglobin. Second, it also better addresses the challenge of the worse signal-to-noise ratio than in the contact-based or active measurement, e.g., caused by background illumination. Signal noise from background illumination is addressed in several ways. The key part is an automated reference measurement of background illumination by automated patient localization in the acquired images by extraction of skin and background regions with a CNN-based detector. Due to the custom spectral ranges, the detector is trained and optimized for this specific setup. Altogether, allowing a contactless measurement, the studied concept promises to improve the care of patients where skin contact has negative effects

Remote Assessment of the Cardiovascular Function Using Camera-Based Photoplethysmography

Camera-based photoplethysmography (cbPPG) is a novel measurement technique that allows the continuous monitoring of vital signs by using common video cameras. In the last decade, the technology has attracted a lot of attention as it is easy to set up, operates remotely, and offers new diagnostic opportunities. Despite the growing interest, cbPPG is not completely established yet and is still primarily the object of research. There are a variety of reasons for this lack of development including that reliable and autonomous hardware setups are missing, that robust processing algorithms are needed, that application fields are still limited, and that it is not completely understood which physiological factors impact the captured signal. In this thesis, these issues will be addressed. A new and innovative measuring system for cbPPG was developed. In the course of three large studies conducted in clinical and non-clinical environments, the system’s great flexibility, autonomy, user-friendliness, and integrability could be successfully proven. Furthermore, it was investigated what value optical polarization filtration adds to cbPPG. The results show that a perpendicular filter setting can significantly enhance the signal quality. In addition, the performed analyses were used to draw conclusions about the origin of cbPPG signals: Blood volume changes are most likely the defining element for the signal's modulation. Besides the hardware-related topics, the software topic was addressed. A new method for the selection of regions of interest (ROIs) in cbPPG videos was developed. Choosing valid ROIs is one of the most important steps in the processing chain of cbPPG software. The new method has the advantage of being fully automated, more independent, and universally applicable. Moreover, it suppresses ballistocardiographic artifacts by utilizing a level-set-based approach. The suitability of the ROI selection method was demonstrated on a large and challenging data set. In the last part of the work, a potentially new application field for cbPPG was explored. It was investigated how cbPPG can be used to assess autonomic reactions of the nervous system at the cutaneous vasculature. The results show that changes in the vasomotor tone, i.e. vasodilation and vasoconstriction, reflect in the pulsation strength of cbPPG signals. These characteristics also shed more light on the origin problem. Similar to the polarization analyses, they support the classic blood volume theory. In conclusion, this thesis tackles relevant issues regarding the application of cbPPG. The proposed solutions pave the way for cbPPG to become an established and widely accepted technology

Robuste Detektion, Verfolgung und Wiedererkennung von Personen in Videodaten mit niedriger Auflösung

Mit der zunehmenden Menge an Bilddaten im Videoüberwachungssektor wächst die Chance, Straftaten besser aufklären zu können. Allerdings ist dafür ein immenser Aufwand für die Auswertung der Bilder erforderlich, die oft nicht mehr vollständig ohne Computerunterstützung durch Personen gesichtet werden können. Diese Arbeit umfasst Methoden und Verbesserungen auf Basis neuartiger Personenrepräsentationen für die Detektion, Verfolgung und erscheinungsbasierte Wiedererkennung von Personen