In one aspect, the present invention provides a contrast enhancement agent comprising an iron chelate having structure I and salts thereof wherein R1 is independently at each occurrence a hydroxy group, a C1-C3 hydroxyalkyl group, or a C1-C3 alkyl group, and b is 0-4; R2-R7 are independently at each occurrence hydrogen, a C1-C3 hydroxyalkyl group, or a C1-C3 alkyl group, with the proviso that at least one of R1-R7 is a hydroxy group or a C1-C3 hydroxyalkyl group; and wherein Q is one or more charge balancing counterions. Also provided are a metal chelating ligand having structure IX and medical formulations comprising the contrast enhancement agent I.