There are increasing concerns about Gadolinium based contrasts safety. One potential alternative agent is endogenous intracellular methemoglobin(MrtHb), a paramagnetic molecule in small amounts in our blood cells. Intracellular levels of MetHb can be increased by exposing blood to nitric oxide or sodium nitrite. The previous in vitro studies suggest that an intracellular MetHb level less than 10% sufficiently increases the T1 signal of blood to be an effective contrast agent. The purpose of this work is to evaluate the change of T1 of blood according to a transient increase in intracellular MetHb in an in vivo animal model.