As expected ICB cleared through the liver and s775cRGD through the kidneys. This proof-ofconcept study highlights the great potential of utilizing deep-red ICB for rapid visualization of the vasculature within cancerous tissue that has been simultaneously stained using cancer targeting near-infrared s775cRGD. Pre-clinical research studies could use this information to assess how microvascular permeability changes with tumor physiology or experimental therapy. Ultimately, it could be incorporated into clinical protocols that determine patient response to treatments that are designed to alter tumor perfusion. In this regard, improved pharmacokinetic insight is gained by using fluorescent agents with varied size since they will be sensitive to different hemodynamic regimes. Since ICB binds strongly to albumin, its effective diameter is the size of the 67 kDa protein. In recent years, several hydrophilic near-infrared fluorophores have been developed with negligible albumin affinity and much smaller hydrodynamic diameters than an ICB/albumin complex. This suggests new classes of