1. A method for imaging using labeled contrast agents and a magnetic resonance imaging (MRI) scanner comprising: performing a prescan on a subject at a resonance frequency selected to be substantially similar to a resonance frequency of a labeled contrast agent, prior to administration of the labeled contrast agent to the subject; performing an examination scan at the resonance frequency of the labeled contrast agent substantially immediately after administering the labeled contrast agent to the subject; and obtaining an image of the subject in order to characterize a metabolic region of interest.