Bridging photon transport regimes in turbid media by accounting for the finite speed of light

The treatment efficacy for numerous human diseases relies on the early diagnosis of tissue pathologies. Some of the associated microscopic histopathological features (e.g., abnormal shape and organization of cells) affect the propagation of light through the tissue, rendering many optical techniques potential screening tools. In this context of early detection and screening, optical techniques that allow highly localized (i.e., microscopic) probing of such light-tissue interaction are most promising: their small interrogation volumes eliminate the influence of the surrounding healthy tissue, thereby rendering these techniques highly sensitive to small superficial lesions. Leveraging this sensitivity in the determination of tissue status, however, necessitates a theoretical light-transport framework (relating the optical signal changes to histopathology). This has so far remained elusive, as the optical signals generally comprise contributions from two distinct light-transport regimes (i.e., subdiffuse and diffuse), stymieing the formulation of a unified theory. Consequently, current models are either empirical or rely on limiting assumptions regarding light propagation (in turn restricting the model validities). Here, we develop and propose the use of a powerful computational framework (which inherently consolidates the subdiffuse and diffuse light-transport regimes) to model such optical signals and theoretically validate and demonstrate the practical feasibility of this approach.