Laser speckle imaging based on photothermally driven convection

Abstract

Abstract. Laser speckle imaging (LSI) is an interferometric technique that provides information about the relative speed of moving scatterers in a sample. Photothermal LSI overcomes limitations in depth resolution faced by conventional LSI by incorporating an excitation pulse to target absorption by hemoglobin within the vascular network. Here we present results from experiments designed to determine the mechanism by which photothermal LSI decreases speckle contrast. We measured the impact of mechanical properties on speckle contrast, as well as the spatiotemporal temperature dynamics and bulk convective motion occurring during photothermal LSI. Our collective data strongly support the hypothesis that photothermal LSI achieves a transient reduction in speckle contrast due to bulk motion associated with thermally driven convection. The ability of photothermal LSI to image structures below a scattering medium may have important preclinical and clinical applications.

Visualization of in vitro deep blood vessels using principal component analysis based laser speckle imaging

“…Usually mid-infrared detectors are used to collect the spatially-dependent infrared emission from skin. In a closely related technique, photothermal LSCI [7,8], a short pulse laser (λ = 595 nm) is used to heat up subsurface blood vessels, so the rapid heating of the molecules causes an increment in the particles motion, which traduces as a decrease in the local speckle contrast. However, in these invasive methods a pulsed laser or external agents are needed to modify the contrast to improve the visualization of blood vessels.…”