Sensitivity of laser speckle contrast imaging to flow perturbations in the cortex

Abstract

© 2016 Optical Society of America. 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, 1=τc, varies across the field of view: directly over surface vessels 1= τc is strongly localized to the single vessel, while parenchymal ROIs have a larger sensitivity to flow changes at depths up to 500mm into the tissue and up to 200mm lateral to the ROI. It is also shown that utilizing the commonly used models the relate 1= τc to flow resulted in nearly the same sensitivity to the underlying flow, but fail to accurately relate speckle contrast values to absolute 1= τc.