Fig. 4.

Fluorescence signal from a green fluorescent protein (GFP)-expressing pancreatic tumor as seen with three different emission filters. A When an interference filter was used, the fluorescence signal was strong, but the background was almost completely blocked out and appeared nearly uniformly black. B Using the OG515 glass filter instead, slightly more background came through, although it was still insufficient for navigation. Also, the color balance with this filter was not optimal. C The use of the GG495 glass filter achieved a good color balance and adequate visualization of the background while maintaining good signal-background contrast