Time-Domain Diffuse Correlation Spectroscopy: from theory to human subject studies

Time-domain diffuse correlation spectroscopy (TD-DCS) is a novel modality which offers dramatic improvements over the capabilities of functional near-infrared spectroscopy (fNIRS) by providing three times higher sensitivity to brain and greatly reduced scalp contamination. We are developing the first wearable, short-separation, gated TD-DCS system. We illuminate the scalp with a pulsed long-coherence length laser and detect photons with a time-gated photon counting detector. The detector is turned on at a specific time delay with respect to the laser pulses to discard the early arriving photons, which have travelled only superficially. This strategy allows us to: Move from the traditional large source-detector pair geometry with the “banana” shaped spatial sensitivity profile to a sub-cm source-detector separation with improved spatial localization, right under the optodes; Improve sensitivity to the brain and reduce scalp contamination by collecting only the photons that have travelled long paths through the brain; Add the measurement of cerebral blood flow (CBF) to conventional fNIRS hemoglobin concentration measurements.