Abstract

We demonstrate the feasibility of time-resolved diffuse reflectance at a small (2 mm) source-detector separation using a single-photon avalanche diode (SPAD) operated in time-gated mode. By time-gating the initial photons, it is possible to detect longer lived photons that have explored deeper the medium even at almost null interfiber distances. We show that the proposed technique is capable to detect a local inhomogeneity embedded within a tissue phantom with a reduced scattering coefficient of 0.63 mm⁻¹ and an absorption coefficient of 0.0093 mm⁻¹ down to a depth >20 mm. Finally, the novel approach proved valuable to detect a task-related brain activation on a volunteer.

© 2008 Optical Society of America