Magnetic Imaging Considerations, Kinetics, and Thermodynamics of Complexes

The effect of the magnetic field strength that is usually low for the MRI experiment (0.5-1.5 Tesla, 1H frequencies of 20-60 MHz,) 

Electronic relaxation rates that are also dependent on field strength 

Hydration number, q, that is, the number of water molecules in the Gd(III) first coordination sphere 

Rotation effects (slower rotation, i.e., larger molecule yields improved relaxivity) 

Researchers have accumulated a large body of thermodynamic and kinetic data to assess these effects, and many of these results are included in the tables of reference 101. Qualitatively, one concludes that for small molecule Gd(III) complexes—those of molecular weight 1000 Da—a high relaxivity, measured in mM 1 s 1, will approach an upper limit of 5 mM-1s-1. Some data are collected in Table 7.3. Newer macromolecular conjugate-Gd(III) complex systems, also discussed below, may approach relaxivities five to six times larger per Gd(III) ion. 

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