Study of Time-Resolved Dynamics in Turbid Medium Using a Single-Cavity Dual-Comb Laser

Abstract

In measuring cerebral blood flow (CBF) noninvasively using optical techniques, diffusing-wave spectroscopy is often combined with near-infrared spectroscopy to obtain a reliable blood flow index. Measuring the blood flow index at a determined depth remains the ultimate goal. In this study, we present a simple approach using dual-comb lasers where we simultaneously measure the absorption coefficient (μ a ), the reduced scattering coefficient (μ s ′), and dynamic properties. This system can also effectively differentiate dynamics from various depths, which is crucial for analyzing multilayer dynamics. For CBF measurements, this capability is particularly valuable as it helps mitigate the influence of the scalp and skull, thereby enhancing the specificity of deep tissue.

Pathlength-selective, interferometric diffuse correlation spectroscopy (PaLS-iDCS)

“…This link is not required in our approach that uses a nearly transform limited, pulsed laser, which enables both a gating function duration within the optimal range for human cerebral blood flow measurements as well as independent selection for the gate center time. Methods utilizing much shorter coherence lengths have also been demonstrated by Safi et al 38 and Zhang et al 39 . In these works, the coherence gate width FWHM was ∼1.4 ps and ∼39 ps, respectively.…”

“…These methods have allowed for major improvements in measurement SNR at extended source-detector separations, though still maintain the link between source-detector separation, measurement SNR, and cerebral sensitivity. Methods designed to decouple this link based on time-of-flight (ToF) discriminative detection have also been developed and include time domain DCS (TD-DCS) 33,34 , interferometric near-infrared spectroscopy (iNIRS) 35,36 , and coherence-gated DCS [37][38][39] , enabling measurements taken at short source-detector separation that take advantage of the greater absolute number of photons which carry information about the cerebral hemodynamics signal as compared to long source-detector separations 40 . In this work, we combine several synergistic improvements to DCS and introduce an improved coherence gated DCS method based on the combination of TD-DCS and iDCS at 1064 nm called pathlength selective, interferometric DCS (PaLS-iDCS), a method utilizing interferometry for coherent gain, to greatly improve measurement performance toward robust monitoring of cerebral blood flow.…”