Figure 18.
The intravenous MRI contrast agent [Gd(DTPA)(H2O)]2−. The paramagnetic 4f7 Gd3+ ion is large (ionic radius 1.2 Å) and can accommodate eight coordinating atoms from the chelating DTPA ligand and a water molecule. Exchange of coordinated water with bulk water is important for producing contrast in the magnetic resonance image.