The effect of dose escalation and temporal analysis of the fluorescence is demonstrated in Fig. 4. The peak of fluorescence in tumors is observed at early times (1–4 h) in a dose-dependent manner and there is significant fluorescence in the glioma tumors for several hours after injection. Moreover, fluorescence in the tumor regions was significantly higher than in the contralateral normal brain, or in the brains of rats that received a sham surgery.Fig. 4.Normalized fluorescent signals are shown for all tumor and normal tissues slices analyzed, at all three dose levels (24.5, 49, 122.5 μg/kg), and at varying times following injection (1 h up to 24 h or 48 h). *P < 0.05, Student’s t test.