ESNF20 and ESNF31 appear to perform well in identifyingnormal AGs across species. At first glance, the performance ofthese molecules in mice appears to be lower than that in pigs.However, the lower SBR in mice is likely the result of varyingpath lengths. AGs in mice are so thin (E1 mm), and thepenetration of NIR light is so deep (45 mm) that thick organslike the kidneys and liver appear much brighter than they are ona per gram basis. In pigs and humans, however, the AG signal isa true reflection of the relative difference in fluorophore uptakeamong the various tissues and organs. The kinetics of uptakeand clearance are also different among species, with the NIRfluorescence of AGs in mice lasting for up to 4 h and the signal inpigs peaking at E30 min.