Time Domain Diffuse Correlation Spectroscopy for Detecting Human Brain Function: Optimize System on Real Experimental Conditions by Simulation Method

Abstract

In order to achieve high-sensitivity time-domain diffuse correlation spectroscopy (TD-DCS) measurement of functional changes in cerebral blood flow, this study applied simulation methods to optimize the TD-DCS system under real experimental conditions (including the consideration of the effects of finite coherence length and non-ideal instrument response function IRF). Under a real experimental condition where the incident power is 75 mW, the source-detector distance is 1.0 cm, and the full width at half maxima of the IRF is 160 ps, we used simulation experiments to investigate the relationship between the contrast of the intensity autocorrelation function ( 2 ) in two brain functional states (i.e., baseline and activation) and TD-DCS system parameters (including , IRF, source-detector distance, gate opening time and gate width).Our simulation results show that both longer and longer integration time are beneficial to a more sensitive detection. With a fixed and integration time, the optimal parameters of gate opening time is 800 ps (relative to the peak time of IRF), and gate width is equal to or larger than 800 ps. This study may be useful for guiding the sensitive measurement of human brain functions (e.g., changes in cerebral blood flow) using the TD-DCS technology.

Functional Time Domain Diffuse Correlation Spectroscopy

“…This further requires the use of photodetectors with low jitter and a sharp temporal response over multiple decades (i.e., lacking a “diffusion tail”). The importance and impact of these instrumentation related factors have been explored by our group and others through both simulations ( Qiu et al, 2018 , 2021 ; Colombo et al, 2019 ; Mazumder et al, 2021 ) and experiments ( Tamborini et al, 2019 ; Samaei et al, 2021a ).…”

“…Previously reported TD-DCS systems ( Pagliazzi et al, 2017 ; Tamborini et al, 2019 ; Colombo et al, 2020 ; Samaei et al, 2021b ) face limitations with respect to detector efficiency and/or the characteristics of the IRF. To address these limitations, and building on our previous work demonstrating the benefits of DCS measurements at 1,064 nm ( Carp et al, 2020 ; Ozana et al, 2021 ), as well as simulation studies by our group ( Mazumder et al, 2021 ) and others ( Qiu et al, 2018 , 2021 ; Colombo et al, 2019 ) indicating the importance of optimizing laser source characteristics for TD-DCS, we developed a high-performance, next-generation TD-DCS system employing a custom 1,064 nm laser source and superconducting nanowire single photon detectors (SNSPDs, overall size of 69 × 49.5 × 113 cm for depth, width, and height, respectively) to maximize measurement performance and enable functional brain imaging. The laser source can deliver an optimized, quasi-transform limited ∼300 ps full width half max (FWHM) laser pulse with average power in excess of 500 mW at 1,064 nm.…”

First-in-clinical application of a time-gated diffuse correlation spectroscopy system at 1064nm using superconducting nanowire single photon detectors

“…An elegant way of separating path-length resolved blood flow is a recent development of time-gated diffuse correlation spectroscopy (TG-DCS) [42], [43], [52]- [60], [44]- [51], which can also quantify (1) absolute blood flow by obtaining the absorption (µ a ) and reduced scattering (µ s ') parameters, which can be used as a priori information during the data analysis for blood flow related parameter quantification. The time-gating aspect allows selecting deeper photons for (2) greater brain blood flow sensitivity without the need for long source-detector separations.…”