Abstract: Ethylene Diamine Hydroxy Phenylacetic Acid (EDHPA) type chelators strongly bind paramagnetic metal ions to provide excellent contrast agents for magnetic resonance (MR) imaging. The magnetic dipole generated by unpaired electrons within the paramagnetic (PM) atom, causes a local reduction in the bulk magnetic field of the MR system. The resulting shortening of the T1 (spin lattice) relaxation time in the hydrogen protons within the area of interest, causes an intense "free induction signal" and a corresponding modulation in the collected scanning data. The tissue of organ of interest appears on the MR display as a high intensity of white area. Background tissue is displayed as darker or lower intensity greys. Each member chelator EDHPA' of the EDHPA family of chelators, is a phenolic analog of EDTA, with variations in the para position radical (PR) of the phenol ring.