In most of the commercially available in vivo imaging systems, the near-infrared (NIR) region ranging from 700 to 900 nm called the therapeutic window (1st-NIR optical window) has been used for deep tissue imaging. In contrast, when excited at 785 nm, only a very weak autofluorescence is observed in the region from 800 to 1000 nm, and almost no autofluorescence is observed over 1000 nm. These findings suggest that the background fluorescence resulting from tissue label-free autofluorescence in the 2nd-NIR and 3rd-NIR optical window are much lower than that in the 1st-NIR optical window. Fluorescence imaging of a mouse lymph system was performed using visible, 1st-NIR and 2nd-NIR fluorescent quantum dots (QDs) labeled with bovine serum albumin to reduce non-specific binding of the QDs to tissues. In the cerebrovascular fluorescence imaging, the fluorescence from the probes should penetrate into brain thorough the scalp and skull.