Macromolecular contrast agents for magnetic resonance imaging - Influence of polymer content in ligand on the paramagnetic properties

Macromolecular conjugates of Gd3+-diethylenetriaminepentaacetic acid with d extran were synthesized from dextran 40 (about 40 kg/mol). Diethylenetriami nepentaacetic acid (DTPA) was coupled to aminated dextran by means of a wat ersoluble carbodiimide and macromolecular conjugates containing DTPA ratios as high as 1.25 mmol/g of polymer were obtained. First, it was found that the polymer had a favourable influence on relaxivity, as at 20 MHz, the r(1 ) longitudinal relaxivity of the Gd3+-complexed macromolecular conjugates w as 2 to 4 times as great as that of free GdDTPA(2-), depending on the DTPA content. Second, r(1) greatly increased with the increase in the conjugate DTPA content, from 7.4 to 15.9 mM(-1)s(-1) for an increase in the DTPA cont ent from 0.36 to 0.96 mmol/g. Further increase in the ligand content had no more effect on relaxivity. (C) 1999 Elsevier Science B.V. All rights reser ved.