Abstract
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. 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, also taking color perception aspects 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 of light attenuation mechanisms affecting the appearance of skin and blood, our investigation contributes to the development of more effective technologies aimed at the noninvasive measurement of the physiological properties of these tissues.
Highlights
Complex optical processes often lead to counter-intuitive material appearances
For our first set of experimental results, we explore the effect of disabling Rayleigh scattering in the papillary dermis on the reflectance and appearance of the baseline skin specimen with and without a subcutaneous vein
The in silico experimental results presented in this paper support the hypothesis that Rayleigh scattering caused by collagen fibrils found in the papillary dermis can play a pivotal role in the bluish appearance of veins
Summary
Complex optical processes often lead to counter-intuitive material appearances Such is the case for the appearance of veins located immediately beneath the skin (Fig. 1), usually referred to as subcutaneous veins. Anderson and Parrish[4] observed that since the ratio of diffuse transmittance to direct transmittance in the stratum corneum and epidermis is characterized by weak wavelength dependence, there is no significant amount of Rayleigh scattering in these tissues. They suggested that a form of scattering characterized by a stronger wavelength dependence could be found in the dermis. It is worth noting that Findlay[5] made a similar observation, he instead referred to scattering in the dermis as the reflection of light by dermal collagen fibers
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