Quantitative Measurement of Static and Dynamic Tissue Optical Properties with Continuous Wave Pathlength Resolved Diffuse Correlation Spectroscopy

Abstract

We demonstrate a new coherence gated Diffuse Correlation Spectroscopy (DCS) instrument for pathlength resolved measurement of flow, and tissue optical properties, using a continuous wave low coherence source and a Mach-Zehnder interferometer.

Optical imaging and spectroscopy for the study of the human brain: status report

“… 81 Path length discrimination, akin to TD-NIRS and TD-DCS, can also be achieved in an interferometric setup by reducing the coherence length of the light source. 82 , 83 …”

“…81 Path length discrimination, akin to TD-NIRS and TD-DCS, can also be achieved in an interferometric setup by reducing the coherence length of the light source. 82,83 The SNR of a single interferometric channel can exceed that of a standard DCS photoncounting channel 80 if the reference light level is high enough. Therefore, with parallel detection, iDWS greatly improves SNR and reduces cost, accessing higher temporal resolution and allowing for measurements at larger source-detector separations.…”

Diffuse correlation spectroscopy: current status and future outlook

“…To improve sensitivity to flow in deep tissues, a number of methods have been proposed to isolate the photons that travel at depth and reject those that only probe superficial tissues. These include time-of-flight selection (time-resolved/time-domain DCS 54 and the related iNIRS technique 55 ), pathlength selection through coherence gating, 56 and acoustic (ultrasound) tagging. 57 , 58 A major advantage of these techniques is that large source-detector separations are no longer needed, enabling compact probe design and/or dense spatial sampling and increased resolution, for example, for functional brain imaging.…”

Interferometric diffuse optics: recent advances and future outlook

“…4(b) ]. 51 TOF filtering reduces the height of , but is beneficial, on balance, as superficial paths can be preferentially attenuated. 52 Thus coherence reduction is a simple approach to achieving TOF filtering or discrimination, which can attenuate scalp photons to enhance brain sensitivity at small S–C separations [ Fig.…”

“…TPSFs provide optical properties, which facilitate recovering absolute BFI. 3 , 23 , 35 Admittedly, any technique providing TOF-resolved CLFs 10 , 40 , 51 can also measure TPSFs and, in principle, with sufficient TOF resolution, quantify optical properties. However, unlike TD-DCS, iNIRS does not suffer from the tradeoff between coherence and TOF resolution 54 and can achieve TOF resolutions of picoseconds 41 with a high dynamic range through spectral shaping.…”