Modern laser speckle contrast theory: flaws and consequences

Abstract

Laser speckle contrast imaging (LSCI) is a non-invasive optical imaging technique for monitoring blood flow in brain, skin, and retina. The simple and cheap instrument makes it a promising technology for both clinical applications and research. Modern LSCI theory takes advantage of the relation between blood flow and the speckle contrast v ~ 1/K^2 to provide an online acquisition of a full-field blood flow image. However, the assumptions about the form of field correlation function, static scattering effect, and the coherence factor make interpretation of the contrast imprecise. Here we examined how the assumptions in modern LSCI theory affect the relative blood flow measurement and utilized Dynamic Laser Speckle Imaging (DLSI) to validate the imprecision of modern LSCI. Most importantly, the contrast models for measuring relative flow in the brain parenchyma and the large vessels were derived. It turns out that modern LSCI underestimates blood flow change and leads to significant error for slow blood flow measurement.