Monte Carlo simulations of the light interaction with blood vessels in human skin in the red wavelength region

• An attempt was made at determining if the elastically backscattered Doppler shifted light from cutaneous blood vessels merely emanates from the peripheral parts, or also from the more central core of these vessels, after illumination by red laser light (632 nm). A multilayered, semi-infinite Monte Carlo model of human skin was constructed accordingly, with separate layers or epidermis, dermis including blood, inferior vascular plexus and subcutaneous fat. Two concentric cylinders of infinite length and with varying diameters, representing core and peripheral parts of a blood vessel, were located at various depths in the skin model, either in the superior or inferior vascular plexus. In order to test the stability of the model predictions, widely varying values of the optical properties were employed in the calculations, trying to encompass most of the extreme values found in the literature. The number of photons Doppler shifted by a fixed size central core of a small blood vessel, is independent of the volume of blood surrounding this core in the rest of the blood vessel, provided the total number of detected photons is maintained constant, and the vessel dimensions are within human physiological limits. For the source/detector system simulated (one optical fiber 700 micrometer diameter), backscattered light Doppler shifted in superficial blood vessels constituted almost all the photons detected, with only very few photons having interacted with the inferior plexus.

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MEDICINE

MEDICIN

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