Electron spin resonance (ESR) and Overhauser-enhanced magnetic resonance imaging (OMRI) studies were carried out for various concentrations of 14N-labeled 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidin-1-yloxy (carbamoyl-PROXYL) in pure water. The ESR parameters and Overhauser enhancement factor were estimated. Line width and line shape analysis confirm that the lines broaden in proportion to agent concentration and are approximately Lorentzian. The contribution of Lorentzian component and Overhauser enhancement factor (OEF) attain maximum in the range of 2.5-3 mM concentration. The agent concentration was optimized as 2.5-3 mM for free radical imaging. The observed spin-spin relaxation time (T2e) decreases with increasing concentration. The isotropic g-values were obtained.