Spatiotemporal Fusion Near-Infrared Spectroscopy Method for Accurate Determination of Optical Properties in Homogeneous Media

In diffuse optics, accurate estimation of the absorption and scattering properties of turbid media remains a persistent challenge, particularly for complex biological tissues. Traditional spatial-domain, time-domain (TD), and frequency-domain (FD) near-infrared spectroscopy (NIRS) methods derive optical properties from single-domain information. However, they are associated with numerous limitations such as nonuniqueness of the optimal solution, lack of depth sensitivity, and susceptibility to interference. Herein, a spatiotemporal fusion NIRS method is proposed to derive the absolute values of absorption and scattering accurately by integrating time and space domain information. The core principle addresses the nonuniqueness of the spatial-domain method by providing continuous observations on the time scale to optimize the spatial-domain solution range using TD information. Simulations based on the diffusion equation (DE) and experiments on liquid phantoms were conducted to verify the principle and validate performance, respectively. The proposed method achieved average absolute relative errors (REs) of 1.00% and 0.96% for the optical absorption and reduced scattering coefficients of homogeneous media, respectively, which is superior to existing methods. Furthermore, this study investigates certain regular phenomena within the methodology and reveals their relationships to the fundamental physics of photon propagation in diffuse media. This method is highly suitable for the currently popular multichannel TD instruments and has good application potential in optical properties retrieval of complex biological tissue.