High-sensitivity multispeckle diffuse correlation spectroscopy.

Edbert J Sie,Mark A Chevillet,E-Fann Saung,Hui Chen,Francesco Marsili,Tobias Tiecke,Ryan Catoen

doi:10.1117/1.nph.7.3.035010

Edbert J Sie, Mark A Chevillet + Show 5 more

Open Access

https://doi.org/10.1117/1.nph.7.3.035010

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Journal: Neurophotonics	Publication Date: Sep 26, 2020
Citations: 36	License type: cc-by

Affiliation: Meta (United States)

Abstract

.Significance: Cerebral blood flow is an important biomarker of brain health and function as it regulates the delivery of oxygen and substrates to tissue and the removal of metabolic waste products. Moreover, blood flow changes in specific areas of the brain are correlated with neuronal activity in those areas. Diffuse correlation spectroscopy (DCS) is a promising noninvasive optical technique for monitoring cerebral blood flow and for measuring cortex functional activation tasks. However, the current state-of-the-art DCS adoption is hindered by a trade-off between sensitivity to the cortex and signal-to-noise ratio (SNR).Aim: We aim to develop a scalable method that increases the sensitivity of DCS instruments.Approach: We report on a multispeckle DCS (mDCS) approach that is based on a 1024-pixel single-photon avalanche diode (SPAD) camera. Our approach is scalable to independent speckle measurements since large-pixel-count SPAD cameras are becoming available, owing to the investments in LiDAR technology for automotive and augmented reality applications.Results: We demonstrated a 32-fold increase in SNR with respect to traditional single-speckle DCS.Conclusion: A mDCS system that is based on a SPAD camera serves as a scalable method toward high-sensitivity DCS measurements, thus enabling both high sensitivity to the cortex and high SNR.

Highlights

Approach: We report on a multispeckle Diffuse correlation spectroscopy (DCS) approach that is based on a 1024-pixel single-photon avalanche diode (SPAD) camera
The multispeckle DCS (mDCS) technique has been pursued in various ways using 28 stand-alone single-photon avalanche diodes (SPADs),[10,26 8] stand-alone SPADs,[27 4] pixels of a 5 × 5 SPAD array,[28] and interferometric near-infrared spectroscopy detecting 20 speckles with a CMOS camera.[29]. While these prior approaches are important proofs of principle of mDCS, the largest improvement in signal-to-noise ratio (SNR) reported so far is an SNR gain of 5.26 Here, we report on a method to perform 1024 independent DCS measurements using a kilopixel SPAD camera, which provides an SNR gain of 32
We have demonstrated a scalable method for mDCS measurements to enhance the SNR gain by a factor of 32 with respect to single-speckle DCS using a kilopixel SPAD camera

Summary

Introduction

Measuring cerebral blood flow noninvasively and with high sensitivity is critical for clinical applications such as measuring the oxygen metabolic rate[1,2] and monitoring intracranial pressure.[3,4] neuroscience applications such as functional activation mapping[5,6] and noninvasive brain–computer interface[7,8] have been pursued primarily using functional magnetic resonance imaging and near-infrared spectroscopy (fNIRS), such applications could in principle benefit from functional cerebral blood flow measurements.[9,10,11] Diffuse correlation spectroscopy (DCS)[12] is a promising noninvasive optical technique for monitoring cerebral blood flow[13,14] and for measuring cortex functional activation during finger tapping[9] and visual stimulation[10,11] tasks. DCS measures deep-tissue dynamics by coupling coherent light into the subject and measuring the fluctuations in the speckle field created by the light diffusing out of the subject.[12,15,16] Increasing the source–detector separation (ρ) of DCS optodes increases the proportion of detected photons that travel beneath the scalp and skull, deep into the brain cortex.[17,18,19] the increase in sensitivity to deep tissue comes at the expense of a decrease

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Conclusion