G. M. Stein. Analysis and optimization of non-contact tissue activity measurements based on color changes. Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT). Masterarbeit. 2018
In many medical devices camera systems are implemented. Some of these devices are e.g. laboratory or surgical microscopes and also endoscopes. In some others they are used to provide an additional feature, like the position tracking in computed tomography or positioning systems in refractive surgery. Often they are used for only one specific purpose, like the above mentioned position controlling, motion tracking or simply to show the image of the actual scenery and record it. These camera systems deliver much more information than is actually used. Extracting just a part of it could lead to valuable additional data without increasing the amount of devices necessary next to the patient. Focusing on surgical microscopes or endoscopes, usually showing tissue, e.g. a wireless detection of the heart rate with camera-based photoplethysmography (cbPPG) is possible, since heart rate and color changes are correlated [1, 2]. Regarding the color changes in a video of the tissue, especially vessels, it might also be possible to extract the blood flow direction or estimating the pulse wave velocity (PWV). Both parameters were valuable information for a doctor, e.g. in order to verify without use of dye the clipping of an aneurysm during surgery. Or, using the PWV estimation, to evaluate the arterial distensibility and using it as a marker of cardiovascular risk in hypertensive patients . The problem is to extract these small signals of color changes and enhance their quality in order to reveal valuable information and visualize it in an appropriate way.