Title: “Modern Laser Speckle Contrast Theory: Flaws and Consequences”
David Boas, PhD – BME (Advisor, Chair)
Darren Roblyer, PhD – BME
Dmitry D Postnov, PhD – BU Neurophotonics Center and Copenhagen University Biomedical Sciences Institute
Laser speckle contrast imaging (LSCI) is a non-invasive optical imaging technique allowing real-time blood flow monitor in brain, skin, and retina. The simple and low-cost instrument makes LSCI a promising technique for clinical application. Modern LSCI technique 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 field correlation function, static scattering effect, and the coherence factor in modern LSCI theory make the technique imprecise. Previous studies have found the v∝1/K^2 method is oversimplified and only appropriate for flow measurement in mid-sized vessels. Here we investigated the impact of these three factors on cerebral blood flow (CBF) measurement in brain parenchyma, mid-sized vessels, and large vessels, and derived the proper contrast models for CBF measurement in various regions. Dynamic laser speckle imaging (DLSI) was used to provide a ground truth of CBF for validating the imprecision of LSCI. It turns out that modern LSCI model underestimates blood flow change, and leads to significant error for flow measurement in brain parenchyma and during stroke.