Dual-slope imaging in highly scattering media with frequency-domain near-infrared spectroscopy

We present theoretical and experimental demonstrations of a novel, to the best of our knowledge, diffuse optical imaging method that is based on the concept of dual slopes (DS) in frequency-domain near-infrared spectroscopy. We consider a special array of sources and detectors that collects intensity ( I ) and phase ( ϕ ) data with multiple DS sets. We have recently shown that D S ϕ reflectance data features a deeper sensitivity with respect to D S I reflectance data. Here, for the first time, we describe a DS imaging approach based on the Moore-Penrose inverse of the sensitivity matrix for multiple DS data sets. Using a circular 8-source/9-detector array that generates 16 DS data sets at source-detector distances in the range 20-40 mm, we show that D S I images are more sensitive to superficial (<5 m m ) perturbations, whereas D S ϕ images are more sensitive to deeper (>10 m m ) perturbations in highly scattering media.