Portable System for Time-Domain Diffuse Correlation Spectroscopy

Abstract

We introduce a portable system for clinical studies based on Time-Domain Diffuse Correlation Spectroscopy (TD-DCS). After evaluating different lasers and detectors, the final system is based on a pulsed laser with about 550 picosecond (ps) pulse width and a coherence length of 38 mm, and two types of single-photon avalanche diodes (SPAD). The higher efficiency of the redenhanced SPAD maximizes detection of the collected light, increasing the signal-to-noise ratio, while the better timing response of the CMOS SPAD optimizes the selection of late photons and increases spatial resolution. We discuss component selection and performance, and we present a full characterization of the system, measurement stability, a phantom-based validation study, and preliminary in-vivo results collect from the forearms and the foreheads of four healthy subjects. With this system we are able to resolve blood flow changes 1 cm below the skin surface with improved depth sensitivity and spatial resolution with respect to continuous wave DCS.

Diffuse correlation spectroscopy measurements of blood flow using 1064 nm light

“…Measurements were obtained using both the CW-DCS and TD-DCS systems on the forehead of an adult volunteer. The 765-nm (or 785 nm) measurements used our standard systems, 39,40 and we delivered 26 mW (28 mW at 785 nm) of average power on the skin surface. The 1064-nm measurements were conducted using the TOPTICA eagleyard single-frequency laser diode for CW-DCS and the Picoquant pulsed seed laser for TD-DCS, both amplified to 90 mW of average power using the Cybel MantaRay fiber amplifier.…”

“…To acquire proof-of-concept data using time-domain diffuse correlation spectroscopy (TD-DCS) at 1064 nm, we modified our previously reported portable TD-DCS system 40 to replace the source and detection components, while reusing the time-tagging and correlation hardware. We used a 1064-nm Picoquant seed laser emitting FWHM pulses with a repetition rate of 80 MHz at an average power of about 5 mW.…”

Time-domain diffuse correlation spectroscopy (TD-DCS) for noninvasive, depth-dependent blood flow quantification in human tissue in vivo

“…According to diffusion theory, the number of diffusively reflected photons decreases exponentially with the square of the SDS 8 . Ideally, we want to keep SDS short ( 1 cm) to improve spatial resolution 9 , but decreasing SDS increases blood flow estimation errors 10 .…”

“…Another promising approach is the time-domain (TD-) DCS 9 , 15 – 18 . Sutin et al introduced this technique and utilized it to probe cerebral blood flow in rodent brains at short cm 15 .…”

Fast and sensitive diffuse correlation spectroscopy with highly parallelized single photon detection

“…Several multi-channel DCS systems have previously been developed to simultaneously detect more signal. For example, a number of 4-channel DCS systems have been reported in prior work to detect blood flow both from humans 29,30 and mice 31 ; Staples et al constructed an 8-channel DCS system using one PMT and seven single photon counting modules 32 ; Johansson et al developed a 5×5 SPAD configuration to demonstrate improved SNR on a milk phantom and an in vivo blood occlusion test 27 , and Dietsche et al implemented a 28-channel DCS setup with multiple single-mode fibers to measure blood flow in deep tissue 28 . The DCS system in the last work has the most parallelized detection channels that we are aware of to date.…”