SPATIALLY-RESOLVED ABSOLUTE DIFFUSE-REFLECTANCE MEASUREMENTS FOR NONINVASIVE DETERMINATION OF THE OPTICAL-SCATTERING AND ABSORPTION-COEFFICIENTS OF BIOLOGICAL TISSUE

The absorption and transport scattering coefficients of biological tis sues determine the radial dependence of the diffuse reflectance that i s due to a point source. A system is described for making remote measu rements of spatially resolved absolute diffuse reflectance and hence n oninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of th e incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measur ements. Instead, a neural network, trained on the results of Monte Car lo simulations, was used to estimate the absorption and scattering coe fficients from the reflectance data. Tests on tissue-simulating phanto ms with transport scattering coefficients between 0.5 and 2.0 mm(-1) a nd absorption coefficients between 0.002 and 0.1 mm(-1) showed the rms errors of this technique to be 2.6% for the transport scattering coef ficient and 14% for the absorption coefficients. The optical propertie s of bovine muscle, adipose, and liver tissue, as well as chicken musc le (breast), were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam. (C) 1996 Optical Society of America