Near-infrared light emitting dyes have the potential for imaging vasculature, tumors, and other objects fairly deep within the body. Indocyanine green is already used for ophthalmic angiographies, liver and cardiac studies, and other applications, but the quality of the image it helps to create can be quite limited.
Dyes based on carbon nanotubes, quantum dots, and other techniques already exist but they stay inside the body for way too long.
