Abstract
Laser speckle contrast imaging has become a ubiquitous tool for imaging blood flow in a variety of tissues. However, due to its widefield imaging nature, the measured speckle contrast is a depth integrated quantity and interpretation of baseline values and the depth dependent sensitivity of those values to changes in underlying flow has not been thoroughly evaluated. Using dynamic light scattering Monte Carlo simulations, the sensitivity of the autocorrelation function and speckle contrast to flow changes in the cerebral cortex was extensively examined. These simulations demonstrate that the sensitivity of the inverse autocorrelation time, [Formula: see text], varies across the field of view: directly over surface vessels [Formula: see text] is strongly localized to the single vessel, while parenchymal ROIs have a larger sensitivity to flow changes at depths up to 500 μm into the tissue and up to 200 μm lateral to the ROI. It is also shown that utilizing the commonly used models the relate [Formula: see text] to flow resulted in nearly the same sensitivity to the underlying flow, but fail to accurately relate speckle contrast values to absolute [Formula: see text].
Highlights
Laser speckle contrast imaging (LSCI) is a powerful, low cost method of imaging dynamic motion with high spatial and temporal resolution
LSCI has been heavily adopted for neuroscience applications such as blood flow imaging of neurovascular pathologies [1, 2], functional activation [3], and even human cortical blood flow imaging during neurosurgery [4,5,6]
The base Monte Carlo simulations of light scattering in each geometry required 200 processors and 7 hours of wall-clock time to run on the Texas Advanced Computing Center (TACC) Lonestar machine
Summary
Laser speckle contrast imaging (LSCI) is a powerful, low cost method of imaging dynamic motion with high spatial and temporal resolution. The dynamic imaging capability of LSCI arises from interactions between coherent photons and tissue. When these photons interact with moving particles, the variance of the detected intensity fluctuations of the speckle pattern changes, which cause spatial blurring when averaging over a fixed exposure duration. This blurring is directly linked to the change in the intensity autocorrelation function g2(t), which in turn is related to sample motion through the field autocorrelation function g1(t). Sequential intravascular scattering has been studied in the context of diffuse correlation spectroscopy, but remains to be examined for LSCI [11]
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