where F is the region of interest (ROI) fluorescence from tumor (F T) and contralateral normal (F N) brain quantified in ImageJ® software (NIH, Bethesda, MD), and background being outside the brain region (F B). The ROI of both tumor region and contralateral normal brain was guided by custom delineation based upon the fluorescence images and confirmed with the hematoxylin and eosin images.