The present invention relates to a novel class of ligands for being applied in paramagnetic ion-based contrast agents of formula e (III) or (IIIa), wherein R is independently H or a C2-C70 aminopolyol moiety comprising a straight or branched alkyl chain substituted by from 2 to 30 hydroxyl groups, the chain being optionally interrupted by one or more groups selected from -0-, -NH-, -N<, -CO-, -CONH-, -NHCO-, -C0N or NC0-; and optionally substituted by one or more C4-C10 cyclic units; L is independently a direct bond or a divalent straight or branched linker moiety between R and the rest of the molecule, comprising at most 20 carbon atoms; v is a positive integer from 1 to 7; together with the corresponding protonated forms of the phosphonate (-PO3H2) and carboxy (-COOH) groups; or a physiologically acceptable salt of such ligand; with the proviso that at least one of the R groups is other than H; the contrast agents show a pharmacokinetic profile analogous to that of the commonly used Tl-general extra vascular agents (NSA) but are further characterized by a higher relaxivity.