Optical assessment of cutaneous blood volume depends on the vessel size distribution: a computer simulation study.

A Monte Carlo simulation was adapted to specify a skin model with pigmented epidermis, dermis with low baseline blood content, and vessels of a vascular lesion with an average added blood volume fraction of 5%. In the study, the lesion vessel diameters were increased and the number of lesion vessels decreased, such that the total lesion blood content was constant. The results show that reflectance (R) increases as vessel size increases, even though the blood content is constant. Light cannot penetrate effectively into larger blood vessels, so the interior of the vessel becomes less visible to the light - a result known in the literature. This study did repeated random placement of vessels to learn the variation in R due to variable vessel placement. The coefficient of variation was about 10% due to random placement. R varies with size, even with small vessels, and does not simply apply to large vessels.