Self-Calibrated Frequency Domain Diffuse Optical Spectroscopy with a Phased Source Array

In this paper, we show that interfering multiple photon density waves created by intensity-modulated sources in frequency domain diffuse optical spectroscopy (fd-DOS) can be used to recover the optical properties of homogenous and heterogeneous tissues. While fd-DOS can recover the optical properties of homogenous tissue using a single source-detector pair, heterogeneous or layered tissues such as breast, brain, and skin require additional source-detector pairs with multiple separations. Through modelling, we show that the varying illumination patterns created by the interference of two intensity modulated sources can be used to recover the optical properties of two-layer tissue using only a single detector and two phased sources. Two-dimensional fd-DOS models of the conventional multi-distance and proposed multi-phase approaches were compared for homogenous and two-layered tissues. In a homogenous tissue with absorption and reduced scattering coefficients representative of human breast, the simulation results showed that both multi-distance and multi-phase approaches are capable of recovering the absorption and reduced scattering coefficients of the tissue. However, the multi-phase approach has less precision than the conventional multidistance approach. In the two-layer model, the multi-phase approach was capable of recovering the optical properties of both layers, while the multi-distance approach could not.