Optimization of time domain diffuse correlation spectroscopy parameters for measuring brain blood flow.

Dibbyan Mazumder,Stefan A Carp,Maria Angela Franceschini,Nisan Ozana,Melissa M Wu,Davide Tamborini

doi:10.1117/1.nph.8.3.035005

Abstract

.Significance: Time domain diffuse correlation spectroscopy (TD-DCS) can offer increased sensitivity to cerebral hemodynamics and reduced contamination from extracerebral layers by differentiating photons based on their travel time in tissue. We have developed rigorous simulation and evaluation procedures to determine the optimal time gate parameters for monitoring cerebral perfusion considering instrumentation characteristics and realistic measurement noise.Aim: We simulate TD-DCS cerebral perfusion monitoring performance for different instrument response functions (IRFs) in the presence of realistic experimental noise and evaluate metrics of sensitivity to brain blood flow, signal-to-noise ratio (SNR), and ability to reject the influence of extracerebral blood flow across a variety of time gates to determine optimal operating parameters.Approach: Light propagation was modeled on an MRI-derived human head geometry using Monte Carlo simulations for 765- and 1064-nm excitation wavelengths. We use a virtual probe with a source–detector separation of 1 cm placed in the pre-frontal region. Performance metrics described above were evaluated to determine optimal time gate(s) for different IRFs. Validation of simulation noise estimates was done with experiments conducted on an intralipid-based liquid phantom.Results: We find that TD-DCS performance strongly depends on the system IRF. Among Gaussian pulse shapes, pulse length appears to offer the best performance, at wide gates (500 ps and larger) with start times 400 and 600 ps after the peak of the TPSF at 765 and 1064 nm, respectively, for a 1-s integration time at photon detection rates seen experimentally (600 kcps at 765 nm and 4 Mcps at 1064 nm).Conclusions: Our work shows that optimal time gates satisfy competing requirements for sufficient sensitivity and sufficient SNR. The achievable performance is further impacted by system IRF with quasi-Gaussian pulse obtained using electro-optic laser shaping providing the best results.

Highlights

The brain of a normal human adult has a high energy demand, receiving 10% to 16% of cardiac output under normal cerebral circulation and cardiac function, while weighing only around 2% NeurophotonicsDownloaded From: https://www.spiedigitallibrary.org/journals/Neurophotonics on 02 Nov 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-useJul–Sep 2021 Vol 8(3)Mazumder et al.: Optimization of time domain diffuse correlation spectroscopy parameters for measuring. . .of the total body mass.[1]
We find that Time domain diffuse correlation spectroscopy (TD-Diffuse correlation spectroscopy (DCS)) performance strongly depends on the system instrument response functions (IRFs)
Our work shows that optimal time gates satisfy competing requirements for sufficient sensitivity and sufficient signal-to-noise ratio (SNR)

Summary

Introduction

The brain of a normal human adult has a high energy demand, receiving 10% to 16% of cardiac output under normal cerebral circulation and cardiac function, while weighing only around 2% NeurophotonicsDownloaded From: https://www.spiedigitallibrary.org/journals/Neurophotonics on 02 Nov 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-useJul–Sep 2021 Vol 8(3)Mazumder et al.: Optimization of time domain diffuse correlation spectroscopy parameters for measuring. . .of the total body mass.[1]. Cerebral autoregulation is a mechanism that assists in maintaining a relatively stable cerebral blood flow (CBF) over a wide range of cerebral perfusion pressures. This protective mechanism becomes impaired under abnormal conditions such as cerebral ischemia, traumatic brain injury, and subarachnoid haemorrhage.[2,3] Impairment of cerebral autoregulation under any circumstances may lead to both hypoperfusion (inadequate CBF) and hyperperfusion (excess CBF) that can result in damage to the patient’s brain.[4] Non-invasive monitoring of CBF at the bedside is needed for CBF management and assessment of CA with the goal of maintaining brain health under these circumstances.[5]

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