Depth-Sensitive Cerebral Blood Flow and Low-Frequency Oscillations for Consciousness Assessment Using Time-Gated Diffuse Correlation Spectroscopy.

This study evaluates the feasibility of depth-sensitive bedside monitoring of cerebral blood flow (CBF) and low-frequency oscillations (LFOs) using time-domain diffuse correlation spectroscopy (TD-DCS) in healthy controls and patients with disorders of consciousness (DOC). A 1064 nm TD-DCS system equipped with superconducting nanowire single-photon detectors (SNSPDs) was used to collect 10-minute resting-state data from 25 healthy adults and 5 patients with traumatic brain injury (TBI) diagnosed with DOC, including minimally conscious state (MCS) and coma, in the subacute phase. Photon arrival times were temporally gated to distinguish superficial and cortical-weighted tissue contributions. The blood-flow index (BFI) was extracted from gated autocorrelation functions, and LFOs were quantified using power spectral density within the Slow-5 (0.01-0.027 Hz), Slow-4 (0.027-0.073 Hz), and Slow-3 (0.073-0.198 Hz) bands. Compared to healthy controls, DOC patients exhibited altered resting-state LFO amplitude and spectral distribution, suggestive of altered neurovascular dynamics in severe brain injury. An auditory "smile" command was delivered to five healthy subjects, one MCS patient, and one unresponsive wakefulness syndrome (UWS) patient to assess task-evoked hemodynamic responses. During the task, healthy participants showed clear hemodynamic responses, whereas DOC patients demonstrated attenuated and more transient responses. Overall, TD-DCS provides a noninvasive, depth-resolved approach for assessing cerebral hemodynamics and residual cortical responsiveness, supporting its potential for bedside neurocritical-care monitoring.