A comparison of diffusive light reflectance from in vitro and in vivo media

The shape of surface reflectance curves is compared for a test medium and for the surface of the human limb. A modulated light spot was incident on the surface of the media and mean reflectance was measured at light source-detector separations ranging from 2.5 mm to 34.5 mm. The in vitro model was constructed to approximate a diffusive layered biological medium. The diffusive properties of the model were changed at depth. Both the in vitro and in vivo results are compared with those predicted by diffusion theory for a uniform diffusive medium. The results indicate that the in vitro medium appears to capture the optical behavior of an in vivo medium for surface measurements out to five diffusion lengths. In addition, the data from both media are matched to the uniform diffusive medium predicted by diffusion theory with good agreement at large source-detector separations