Some ligands and complexes are also useful as oral care agents and as state. To better understand this invention, a brief background on MRI is provided in the following section. Background MRI is a non-invasive diagnostic technique which produces well resolved eross-sedional images of soft tissues within an animal body, preferably a human body. This technique is based upon the property of certain atomic nuclei e. Barrow, Physical Chemistry. Once 1 S aligned, this equilibrium state can be perturbed by applying an external radio frequency RF pulse which causes the protons to be tilted out of alignment with the magnetic field.
When the RF pulse is terminated, the nuclei return to their equilibrium state and the time required for this to occur is known as the relaxation time.
Since the water content of living tissue is substantial and variations in content and environment exist among tissue types, diagnostic images of biological organisms are obtained which reflect proton density and relaxation times.
The greater the differences in relaxation times T1 and T2 of protons present in tissue being examined, the greater will be the contrast in the obtained image [l. Magnetic Resonance 33, 1. It is known that paramagnetic chelates possessing a symmetric electronic ground state can dramatically affect the T1 and T2 relaxation rates of juxtaposed water protons and that the effectiveness of the chelate in this regard is related, in part, to the number of unpaired electrons producing the magnetic moment [Magnetic Resonance Annual, , Raven Press, NY ].
It has also been shown that when a paramagnetic chelate of this type is administered to a living animal, its effect on the T1 and T2 of various tissues can be directly observed in the magnetic resonance MR images with increased contrast being observed in the areas of chelate localization. It has therefore been proposed that stable, non-toxic paramagnetic chelates be administered to animals in order to increase the diagnostic information obtained by MRI [Frontiers of Biol.
