INFLUENCE OF LAYERED TISSUE ARCHITECTURE ON ESTIMATES OF TISSUE OPTICAL-PROPERTIES OBTAINED FROM SPATIALLY-RESOLVED DIFFUSE REFLECTOMETRY

Most instruments used to measure tissue optical properties noninvasive ly employ data-analysis algorithms that rely on the simplifying assump tion that the tissue is semi-infinite and homogeneous. The influence o f a layered tissue architecture on the determination of the scattering and absorption coefficients has been investigated in this study. Refl ectance as a function of distance from a point source for a two-layere d tissue architecture that simulates skin overlying fat was calculated by using a Monte Carlo code. These data were analyzed by using a diff usion theory model for a homogeneous semi-infinite medium to calculate the scatter and absorption coefficients. Depending on the algorithm a nd the radial distance, the estimated tissue optical properties were d ifferent from those of either layer, and under some circumstances, phy sically impossible. In addition, the sensitivity and cross talk of the estimated optical properties to changes in input optical properties w ere calculated for different layered geometries. For typical optical p roperties of skin, the sensitivity to changes in optical properties is highly dependent on the layered architecture, the measurement distanc e, and the fitting algorithm. Furthermore, a change in the input absor ption coefficient may result in an apparent change in the measured sca tter coefficient, and a change in the input scatter coefficient may re sult in an apparent change in the measured absorption coefficient. (C) 1998 Optical Society of America.