On the Bluish Appearance of Veins

The bluish appearance of veins located immediately beneath the skin has long been a topic of interest for biomedical optics researchers. Despite this interest, a thorough identification of the specific optical processes responsible for this phenomenon remains to be achieved. In this paper, we employ controlled in silico experiments to address this enduring open problem. Our experiments, which are supported by measured data available in the scientific literature, are performed using first-principles models of light interaction with human skin and blood. Using this investigation approach, we quantitatively demonstrate that Rayleigh scattering caused by collagen fibrils present in the papillary dermis, a sublayer of the skin, can play a pivotal role in the bluish appearance of veins as suggested by previous works in this area. Moreover, taking colour perception aspects also into account, we systematically assess the effects of variations in fibril radius and papillary dermis thickness on the coloration of veins under different illuminants. Notably, this assessment indicates that Rayleigh scattering elicited by reticulin fibrils, another type of fibril found in the papillary dermis, is unlikely to significantly contribute to the bluish appearance of veins. By strengthening the current understanding about light attenuation mechanisms affecting the appearance of skin and blood, our investigation contributes for the development of more effective technologies aimed at the noninvasive measurement of the physiological properties of these tissues

On Skin Cyanotic Appearances and Spectral Responses Elicited by Methemoglobinemia and Sulfhemoglobinemia

Methemoglobinemia and sulfhemoglobinemia are potentially life-threatening blood disorders characterized by similar symptoms and markedly distinct treatment procedures. In this thesis, we investigate the causal relationship between these disorders and the onset of cyanosis (purple or bluish skin coloration). More specifically, we perform controlled experiments to elicit cyanotic appearances resulting from different severity levels of these disorders and varying physiological conditions. We note that such experiments cannot be induced in living subjects without posing risks to their health. Accordingly, we have resorted to an in silico experimental approach supported by biophysical data reported in the biomedical literature. Besides bringing new insights about cyanotic chromatic variations elicited by methemoglobinemia and sulfhemoglobinemia, our investigation provides the basis for the proposition of a cost-effective protocol for the noninvasive detection and differentiation of these disorders. Our experimental results indicate that its sensitivity range exceeds the range of similar technologies, which are in general associated with high operational costs. We believe that these aspects make the proposed protocol particularly suitable for incorporation into noninvasive disease screening/diagnostic systems, particularly those deployed at the point of care of medical settings with limited access to laboratory resources