Contrast Ratio during Visualization of Subsurface Optical Inhomogeneities in Turbid Tissues: Perturbation Analysis

Visualization and monitoring of the capillary loops and microvasculature patterns in dermis and mucosa are of interest for various clinical applications, including early cancer and shock detection. We developed an approach for the assessment of the contrast ratio during the visualization of subsurface optical heterogeneities. Using the diffuse approximation and perturbation analysis, we considered light absorption heterogeneities as negative light sources. We estimated the contrast ratio as a function of the surface layer's optical properties for diffuse and collimated wide beam illumination. Based on findings, we formulated several practical suggestions: a) proper selection of camera (with maximum dynamic range) is of paramount importance, b) narrow-band illumination is more efficient than white light illumination, and c) use of collimated light provides up to 60% improvement in contrast vs. diffuse illumination. Obtained results can be used for the optimization of imaging techniques