The success of a fluorescence-guided brain surgery is highly dependent of the tumor-to-normal brain fluorescence contrast, and the results are presented in Fig. 6. The contrast relative to the normal brain is dependent on the dose given and the time of data acquisition after dose administration. In our study, the contrast varied from 7 to 16 in the first 4 h. After 24 h, in the microdose level, the contrast is reduced by a factor of 3 to 2.7 resulting in a very low fluorescence intensity. However, with higher administered ABY-029 doses (two or five the microdose level), the contrast level decreased only slightly over time.Fig. 6.The tumor-to-normal brain contrast values are expressed as mean values ± standard error of mean using the ratio of data from Fig. 4 for each injection concentration and time point studied.