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Session: Poster Session 1 (Even numbers)
Session starts: Thursday 26 January, 16:00
Presentation starts: 16:00

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Raquel Alves (TU/e)
Fokke van Meulen (TU/e)
Mark van Gastel (Philips)
Wim Verkruijsse (Philips)
Sebastiaan Overeem (TU/e)
Sveta Zinger (TU/e)
Sander Stuijk (TU/e)

Abstract:
In a polysomnography exam, patients get their vital signs monitored through sensors attached to their bodies. The inconvenience of contact sensors can be partially overcome with the use of thermal cameras. Thermal cameras can monitor respiration motion and flow, by detecting chest movements and temperature variations caused by breathing airflow [1]. It is important to understand how many cameras should be used and where they should be placed. This study used 6 low-cost/low-resolution cameras to collect data from 25 subjects. The cameras were positioned around a bed where subjects were asked to lay in different sleeping positions and breathe at a normal rhythm, either through the nose, mouth or with a nasal cannula. A respiration belt was used as a reference. The respiration signal was extracted from the videos using the algorithm from [1]. It extracts three features from the thermal videos to define a region of interest where the respiration signal is the average pixel intensity over time. The algorithm can use the input from a single camera or a combination of cameras to estimate respiration. To understand how the estimated respiration signal changes when different camera positions are combined, all possible combinations were tested. To evaluate the results, the relative error, precision, and sensitivity values were computed. These last two metrics were computed considering the detection or missed detection of each breath individually. The results show a lower relative error (8.52%) and a higher precision (91.95%) and sensitivity (96.47%) when combining the cameras located behind the headboard with the cameras on the side of the bed. Using the maximum number of cameras does not result in the best outcome. Results also show that breathing through the nose or a nasal cannula often leads to a lower measurement error. There were no significant differences detected between the results of the two sleeping positions tested (supine and lateral). This is the first study that gathers information essential for a conscious placement of thermal cameras for use in future studies and clinical applications. It not only describes the best setup but also gives possible alternatives when considering placement constraints.