An interesting result observed in this study was the increase in the contralateral normal brain fluorescence as a function of tumor area for the animals that received 5-fold larger dose than the initial dose (Fig. 5b), which could be correlated to the transport, likely due to edema, leading to nearly 10-fold higher uptake in the tumor, and approximately a 2-fold increase in tumor to normal tissue contrast. Curiously, at the lower injected dose of 24.5 μg/kg, the increase in normal brain uptake with tumor size was not as apparent, but this could have been due to the lower leakage rates into the tissue from lower concentration. In the cases of larger tumors, the ABY-029 uptake in the background normal brain presented in the extracellular matrix by the cerebrospinal fluid to intact areas of the brain, as seen in Fig. 5c. Similar results have been documented with PpIX fluorescence imaging near glioma tumors . More importantly, though, this increased background from edema-based perfusion to normal brain did not significantly decrease the tumor˗-to-normal contrast (Fig. 6), and a high contrast could be seen even after 24 h post-injection, which is important to cover all possible times for surgical use.