Lookup-table method for imaging optical properties with structured illumination beyond the diffusion theory regime

Sinusoidally structured illumination is used in concert with a phantom-based lookup-table (LUT) to map wide-field optical properties in turbid media with reduced albedos as low as 0.44. A key advantage of the lookup-table approach is the ability to measure the absorption $(μa)$ and reduced scattering coefficients $(μs′)$ over a much broader range of values than permitted by current diffusion theory methods. Through calibration with a single reflectance standard, the LUT can extract $μs′$ from $0.8to2.4mm−1$ with an average root-mean-square (rms) error of 7% and extract $μa$ from $0to1.0mm−1$ with an average rms error of 6%. The LUT is based solely on measurements of two parameters, reflectance $R$ and modulation $M$ at an illumination period of $10mm$. A single set of three phase-shifted images is sufficient to measure both $M$ and $R$, which are then used to generate maps of absorption and scattering by referencing the LUT. We establish empirically that each pair $(M,R)$ maps uniquely to only one pair of $(μs′,μa)$ and report that the phase function (i.e., size) of the scatterers can influence the accuracy of optical property extraction.