Tissue Sensing by Structured Illumination in Optical Diffuse Reflectometry

In this work we studied the efficiency of spatially modulated illumination in optical diffuse reflectometry (ODR) and analyzed various probing patterns. The optimal illumination pattern was determined from the series of Monte Carlo numerical experiments on structured illumination and comparison of the parameters of fluence distribution within tissue. We considered the following illumination profiles: sinusoidal patterns with different spatial frequencies k (1 - 2.5 mm-1); piecewise constant patterns with the fixed duty cycle w = 2 and various strip width (0.2 – 1 mm); piecewise constant patterns with the fixed strip width (0.1 mm) and various duty cycle (3 – 11). Assuming the same total incident intensity for all patterns, we observed the growth in intensity at depth with decreasing value of spatial frequency for sinusoidal pattern, the similar tendency of intensity distribution was for piecewise constant patterns with the fixed strip width (or duty cycle) and duty cycle increase (or increase of a strip width, respectively). The intensity distributions within the sample are almost identical for sinusoidal and piecewise constant patterns with matching peaks and lows. However, probing by piecewise constant profile of illumination provide more local information about sample’s properties. A prototype of an ODR system for probing with the structured illumination was designed. The system consists of PC-controlled optical projection system, polarization filters and a CCD camera. The approbation of the system was carried out on the optical phantoms with optical properties close to those of biological tissues and on skin of human volunteers.