Fig. 3.

Trans-illumination maintains linear relationship between normalized speckle index (NSI) and increases sensitivity to deeper velocity signals in vitro. (a) Line graph of NSI for both epi-illumination (closed squares) and trans-illumination (open circles) configurations ($n=5$ independent trials) as a function of known blood velocity. Both configurations demonstrated similar and highly linear relationships. (b) Graph of speckle velocity (${\mathrm{NSI}}_x$), normalized to surface speckle velocity (${\mathrm{NSI}}_0$), as a function of depth for epi-illumination and trans-illumination and fitted with an exponential relationship (line). *$p<0.05$ between epi- and trans-illumination at the same depth.