Quantitative Velocity Estimates via Laser Speckles

Optical techniques can fail in opaque fluids. Although other physical methods of analysis do exist, such as ultrasound and magnetic resonance imaging (MRI), optical techniques are often preferred due to their full-field measurement capability and their advanced image processing algorithms at a relatively portable scale. We introduce a novel technique to obtain a quantitative velocity field from coherent speckle patterns in steady pressure-driven flow. These patterns are formed using a red spectrum light-emitting-diode laser, projected on the surface of clear tubing carrying a bio-inspired emulsion mimicking the scattering properties of blood. Taking inspiration from laser-speckle contrast imaging (LSCI), in addition to particle image velocimetry (PIV), we present a framework to track intensity changes in the natural light scattering media present in the flow, without the need of adding tracing particles. These data show that by using this technique, a velocity field can reliably be calculated with high spacial resolution. We compare our technique to an analytical model of plane-Poiseuille flow for our experimental setup. The implications of our technique could potentially be significant in measuring blood flow non-invasively in-vivo.