Absorbance of opaque microstructures in optically diffuse media

In this study experimental measurements are used to determine that the obse rved absorbance of opaque microstructures in optically diffuse media correl ates with the total surface area rather than the attenuation as calculated in a nonscattering environment. The data suggest that it may be possible to use remote measurements of optical diffuse transmission to quantify surfac e areas of microcapillaries that are highly absorbing or larger blood vesse ls that can have high intrinsic attenuation because of hematocrit alone. Re sults obtained in a transmission geometry are insensitive to the position o f the microstructure along the line between source and detector, whereas th ose collected in a remission geometry are highly sensitive to the depth at which the structure is located. These types of measurement involving micros copic structures embedded in diffuse media have potential application in qu antifying blood vessel surface areas that contain contrast agents or other microparticles within tissue. (C) 2001 Optical Society of America.