Analyses of the sampling volume for fiber optics and confocal detecting probe in back scattered spectral investigations of the skin

Photon migration through skin tissue leads to a poorly defined "sampling volume" so that the optical signal represents a spatial average over cell layers 1 mm deep or more. This problem is well known in the field of Laser Doppler Flowmetry. The current work is to theoretically investigate to what extent we can localise the sampling volume of reflectance spectroscopy to the upper layers of skin (e.g. the capillary loops). The results of Monte Carlo simulation of the degree of photon spatial localisation for different kind of optical probes are given. Such localisation is very important for the clinical interpretation of the results, as capillary loops are responsible for the delivery of nutrients to the epidermis, whereas deeper vessels are primarily thermoregulatory in function.