Diagnoses of skin diseases are considerably difficult tasks due to the multiply-folded factors. Nailfold capillaroscopy has been developed to diagnosis microvascular disturbances mainly in connective tissue diseases, including systemic sclerosis, dermatomyositis, systemic lupus erythematosus, and Raynaud’s phenomenon. Capillaroscopy is non-invasive, easy to use, low cost and suitable for observation of these typical phenomena. We improved conventional capillaroscopy by constructing “high speed digital video capillaroscopy”, by integrating high speed digital video camera, deep-focus zoom lens, appropriate light source and light collecting adaptor. High speed digital video camera enabled us to observe the individual red blood cell in human nailfold capillary in vivo. The light collecting adaptor is effective for preventing skin from excessive light exposure, which causes serious damage. The first objective of this study is to extract the shape of nailfold capillary quantitatively by using binarization and the level-set method. By using the level-set method, the function, which distinguishes outside from inside of the capillary and also evaluates radius distribution along the capillary center line, is calculated. Based on this mathematical description of capillary shape, more rigorous definition of the capillary red blood cell velocity than the conventional method is obtained. The second objective of this study is to propose the innovative measurement method of red blood cell velocity in nailfold capillary. As plasma gaps show high brightness we trace them and estimate the velocities of blood cells on the center line of capillary. The last objective of this study is to observe the behavior of red blood cell. We evaluate the movement of individual red blood cell, not only in the axial direction but also the lateral direction. We analyze the series of images of red blood cells in capillary and discuss their behavior.

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