Beneath the surface: revealing deep-tissue blood flow in human subjects with massively parallelized diffuse...

Area of Science:

• Biomedical Optics
• Medical Imaging
• Neuroscience

Background:

• Diffuse correlation spectroscopy (DCS) enables label-free, non-invasive investigation of microvascular dynamics, including cerebral blood flow (CBF).
• The signal-to-noise ratio (SNR) in conventional DCS limits its sensitivity for deep tissue measurements, particularly in adults due to greater scalp and skull thickness compared to infants.

Purpose of the Study:

• To enhance the SNR and sensitivity of DCS for measuring cerebral blood flow (CBF) in adults.
• To demonstrate a novel parallelized DCS (PDCS) technique using large arrays of single photon avalanche diodes (SPADs).

Main Methods:

• Developed and demonstrated an in vivo parallelized DCS (PDCS) system utilizing a large array of SPADs to increase SNR through pixel measurement averaging.
• Tested the PDCS device on healthy adults, varying pixel counts and frame rates, with a secondary array for reference measurements from shallower tissues.
• Employed different technical configurations for control experiments measuring muscular blood flow in the forearm.

Main Results:

• The PDCS system successfully measured pulsatile blood flow in cerebral and muscular tissues at source-detector separations up to 4 cm.
• The new system maintained comparable measurement noise to a previous PDCS system but with a significantly larger source-detector separation (4 cm vs. 1.5 cm).
• Experimental data from 15 adults showed functional CBF activity during a cognitive memory task and enabled analysis of pulse markers, with forearm muscle blood flow experiments providing converging evidence.

Conclusions:

• Successful PDCS measurements using large SPAD arrays enable the detection of CBF in human adults.
• Advancements in SPAD camera technology and data processing techniques are expected to further increase SNR and depth sensitivity of PDCS.
• This technology holds promise for improved non-invasive monitoring of microvascular dynamics in various physiological and pathological conditions.