Unwanted movement bias evaluation for multiple exposure speckle imaging of blood flow using the synthetic exposure approach

Multiple exposure speckle imaging (MESI) allows to map relative blood flows at the surface of biological tissues. We have evaluated how a synthetic exposure acquisition scheme could simplify the instrumentation for MESI. This study allowed to propose guidelines in terms of noises, spatial response uniformity and frames rate for the choice of a camera for MESI in the synthetic exposure mode. Furthermore, we have measured how unwanted movements bias the speckle contrast calculation. The effects of the unwanted movement speeds and directions have been evaluated. The results show that in synthetic exposure MESI, the bias introduced by unwanted lateral movement depends on the interframe duration and the scatterers decorrelation time. However, for axial movements, parameters such as the numerical aperture and the magnification level need to be considered due to their role in defining the depth of field and thus impacting speckle contrast values.