Fig. 4.
Validation of local region size for accurate measurement of speckle contrast K. (a) Schematic representation of local region size, where Ns is the number of pixels in the spatial dimension and Nt in the temporal dimension (total number of pixels: Ns × Ns × Nt) for which K is calculated. (b) Mean <K>, as calculated from 45 K-values selected in the processed speckle contrast image from the channel (in vitro) or vessel (in vivo) area. The dashed line represents the global K value.(c) Coefficient of variance (CV = σ K/<K>), where σ K is the standard deviation in the 45 K-values. Both <K> and CV are plotted versus Ns, for 4 different temporal dimensions Nt. All images were recorded at exposure time 1 ms.