Diffuse correlation spectroscopy (DCS) is a well-established method that measures rapid changes in scattered coherent light to monitor cerebral blood flow at the clinical bedside. However, conventional DCS systems become photon-limited when attempting to probe deep into the tissue, leading to long measurement windows and, consequently, a low refresh rate (less than 1 Hz). In this project (Liu et al., 2021), we present a high-sensitivity DCS system with parallel detection channels integrated within a single-photon avalanche diode (SPAD) array, demonstrating the ability to detect mm-scale perturbations underneath the adult human skull at up to a video sampling rate.
The experimental setup and results of the human prefrontal cortex activation test. (a) The schematic diagram of the experimental setup. (b) The plot of the decorrelation time values over the 15 min test including two reading stages and one intermediate rest stage, where 10 s of the signal is collected every minute. (c) The plot of mean decorrelation time corresponding to (b). Each mean decorrelation time value is obtained by averaging all the decorrelation time values within the corresponding 10 s window. (d) Mean ± SD results of the mean decorrelation time of 4 subjects calculated after dividing the data of each subject by the average decorrelation value of their respective measurement sequence. Solid horizontal lines represent the average of the five normalized decorrelation times in each stage
(Liu et al., 2021).
In addition, we extend this work to simultaneously monitor the temporal dynamics of speckle fluctuations at the single-photon level from 12 different phantom tissue surface locations delivered via a customized fiber bundle array, to create video of scattering dynamics beneath rapidly decorrelating tissue phantoms (Xu et al., 2022), or, to accurately detect and classify different transient decorrelation events (Xu et al., 2022).
Flow diagram of proposed method for imaging temporal decorrelation dynamics. (a) Illustration of parallelized diffuse correlation imaging (PaDI) measurement strategy. Scattered coherent light from source to multiple detector fibers travels through decorrelating scattering media along unique banana-shaped paths. Fully developed speckle on the tissue surface rapidly fluctuates as a function of deep-tissue movement. Green dashed box marks deep-tissue dynamics areas of interest for imaging. (b) Computed autocorrelation curves from time-resolved measurements of surface speckle at different tissue surface locations. (c) Autocorrelation variations caused by deep-tissue dynamics are computationally mapped into spatially resolved images of transient dynamics.
(Xu et al., 2022) References
2022
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Imaging Dynamics Beneath Turbid Media via Parallelized Single-Photon Detection
Shiqi Xu, Xi Yang , Wenhui Liu , Joakim Jönsson , Ruobing Qian , Pavan Chandra Konda , Kevin C Zhou , Lucas Kreiß , and 3 more authors
Advanced Science, 2022
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Transient motion classification through turbid volumes via parallelized single-photon detection and deep contrastive embedding
Shiqi Xu, Wenhui Liu , Xi Yang , Joakim Jönsson , Ruobing Qian , Paul McKee , Kanghyun Kim , Pavan Chandra Konda , and 3 more authors
Frontiers in neuroscience, 2022
2021
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Fast and sensitive diffuse correlation spectroscopy with highly parallelized single photon detection
Wenhui Liu , Ruobing Qian , Shiqi Xu, Pavan Chandra Konda , Joakim Jönsson , Mark Harfouche , Dawid Borycki , Colin Cooke , and 3 more authors
APL Photonics, 2021
Imaging Dynamics Beneath Turbid Media via Parallelized Single-Photon DetectionAdvanced Science, 2022
Transient motion classification through turbid volumes via parallelized single-photon detection and deep contrastive embeddingFrontiers in neuroscience, 2022
Fast and sensitive diffuse correlation spectroscopy with highly parallelized single photon detectionAPL Photonics, 2021