Time domain diffuse correlation spectroscopy with a high coherence pulsed source: in vivo and phantom results

Abstract

Diffuse correlation spectroscopy (DCS), combined with time-resolved reflectance spectroscopy (TRS) or frequency domain spectroscopy, aims at path length (i.e. depth) resolved, non-invasive and simultaneous assessment of tissue composition and blood flow. However, while TRS provides a path length resolved data, the standard DCS does not. Recently, a time domain DCS experiment showed path length resolved measurements for improved quantification with respect to classical DCS, but was limited to phantoms and small animal studies. Here, we demonstrate time domain DCS for studies on the adult forehead and the arm. We achieve path length resolved DCS by means of an actively mode-locked Ti:Sapphire laser that allows high coherence pulses, thus enabling adequate signal-to-noise ratio in relatively fast (~1 s) temporal resolution. This work paves the way to the translation of this approach to practical use.

Time-Gated Single-Photon Detection in Time-Domain Diffuse Optics: A Review

“…However, to recover the absolute blood flow value, it is fundamental to know the optical properties of the tissue under analysis [150][151][152]. For this reason, in literature the use of a DCS system coupled to TD or frequency-domain spectroscopic instruments have been proposed [153,154]. Additionally, the CW DCS systems suffer from confounding effects introduced by extracerebral flow due to systemic physiological changes.…”

“…Additionally, the CW DCS systems suffer from confounding effects introduced by extracerebral flow due to systemic physiological changes. In 2016 Sutin et al [153], introduced for the first time the use of TD DCS in phantoms and on rats, while Pagliazzi et al [154] extended the method also on humans with first in-vivo studies on the adult forehead and arm. In all those cases, a post-processing time-windowing of the whole DTOF was applied to improve the autocorrelation of the speckles fluctuation, as well as the sensitivity to deeper layer of the tissue.…”

Effects of the instrument response function and the gate width in time-domain diffuse correlation spectroscopy: model and validations

“…By exploiting the relationship between photon ToF and mean penetration depth, 3,4 depth-discrimination in the BF can be enabled, which is the first advantage of the newly emerging time-domain (TD) DCS with respect to standard (i.e., CW) DCS. 5,6 A second advantage is the parallel estimation, using the same probe, of the tissue optical properties. This has been shown to increase the accuracy of the BF estimation 7 and allows, by using more than one wavelength, the determination of oxy-and deoxyhemoglobin concentrations alongside BF.…”

A multipixel diffuse correlation spectroscopy system based on a single photon avalanche diode array

“…Multilayer modeling has been developed to separate blood flows at different depths and coherence‐maintaining laser pulsing has been used to perform simultaneous time‐resolved spectroscopy and DCS. The latter technique may also provide separation of flows at different depths . The new idea proposed in this study is to use a multiple pixels as in LDF for DCS for estimates of blood flow changes.…”