Low molecular weight polysaccharide complexes for nuclear magnetic resonance imaging

There is disclosed an imaging agent for diagnosis comprising a compound composed of a polynuclear type compound of the formula I or II: ##STR1## wherein each X is a hydrogen atom or a bifunctional ligand, at least one of them are bifunctional ligand and m or n is an integer of 1 to 6, and at least one metal ion being coordinated with at least one bifunctional ligand moiety, said metal ion being selected from the group consisting of metal ions having the atomic number of 21-29, 31, 32, 37-39, 42-44, 49 and 56-83.