Non-invasive detection of tumor hypoxia using radiolabeled
2-nitroimidazoles has been a major effort during the last two decades.
Recent years have witnessed the introduction of several new compounds
which are chemically related to [(18)F]fluoromisonidazole (FMISO) but
show slight but distinct differences in biodistribution and metabolic
clearance. Although [(18)F]FMISO has shown clinical potential it suffers
from suboptimal oxygen dependent tissue contrast and newer agents seek
to improve this essential feature. The limited data on other interesting
tracers keeps the investigators busy at demonstrating the potential
advantages over [(18)F]FMISO while efforts should start to concentrate
on proving the clinical significance of such techniques in the form of
outcome data from image-guided therapy modification. We review here our
experiences with two hypoxia-avid agents
[(18)F]fluoroerythronitromidazole (FETNIM) and [(18)F]
2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide
(EF5) and focus on the similarities and differences of these two tracers
in comparison to other radiolabeled 2-nitroimidazoles. It is recognized
that only [(18)F]FMISO has thus far shown clinical utility and newer
tracers need to be tested against this circumstance.